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有关Fhb1 gene (PFT) 的争议
mashengwei 2018-3-6 14:41
本期作者:Rui Wang 今天会涉及到三篇文章,前两篇我们一月份在 漫谈小麦赤霉病 中介绍过,其中包括2016年NG上的Fhb1 gene克隆文章以及南农马老师课题组2017年在The Crop Journal上发表的一篇综述,第三篇是最近发表在Phytopathology 上的 PFT gene验证文章。 首先Nature Genetics上的基因克隆文章,题目是Wheat Fhb1 encodes a chimericlectin with agglutinin domains and a pore-forming toxin-like domain conferring resistance to Fusarium head blight。这篇文章的重要性以及各个精彩的实验过程我就不再赘述了。总体来说,作为一篇中规中矩的基因克隆文章,在拿到基因后用三方面来验证,包括mutation analysis , RNAi-induced gene-silencing studies,以及overexpression with transformation of wheat。按说是没有什么可挑剔的,可是文章刚一发出来,就立即引起一些争议,其中小编亲耳听到的一点就是:通过测序,这个基因的抗性allele在美国,欧洲很多的小麦材料中都有出现,而客观情况是我们都知道美国以及欧洲的材料很少有 Fhb1 抗性的,事实上美国很多实际应用的抗性都是来源于望水白和苏麦3号。 现在回过头来看NG这篇文章,其实作者们已经预料到了类似的问题,所以文章中有一个Supplementary Table 6,作者们挑了40个不同抗性水平的cultivar和 l andrace,其中也包括国内的很多材料,而得到的结果也堪称完美:22个抗性材料都含有 PFT gene 的抗性allele,而其余的18个感性材料都在这个PFT位点存在变异或者是null allele。 请点击输入图片描述 可是问题就出在这:首先说,这四十个材料是怎么选的,文章没有提及,其次,作者在原文中说用这40个材料做了一个association study。 可是对于一个association study来说,40个材料是不是有点少?材料中的diversity是不是足够?这些都没有交代。 联系到我在上文所提到的争议,NG这篇文章能得到这么完美的结果真的是太不容易(诡异)了!因为其他课题组用PFT去筛选不同种质资源的时候,得到的表型和基因型的相关性其实是非常差的。其中就包括我们要说到的南农马老师的这篇综述,题目是A journey to understand wheat Fusarium head blight resistance in the Chinese wheat landrace Wangshuibai,关于表型和基因型的非相关性,作者列举了三种情况: 1. PFT 基因序列在感病材料PH691和抗性材料望水白、苏麦3号之间完全一致; 2. 在某组重组自交系里,一个具有望水白 PFT 类型的家系却是感病; 3. 44个地方品种材料的 PFT 基因序列与望水白和苏麦3号一致,然而却只有12个表现为抗病类型 总结来说就是:有PFT基因也不一定是抗病的!!! 然后接下来就是最新发表的文章,题目是Molecular Characterization and Expression of PFT, an FHB Resistance Gene at the Fhb1 QTL in Wheat,完成单位是江苏农科院粮食作物研究所,第一作者是Yi He,通讯作者是Hongxiang Ma。文章的内容还是比较丰富的,比如有很多gene表达数据,但是我只节选了gene 在不同种质资源中验证这部分。 材料和方法: 348个材料:A total of 348 wheat accessions originating from China (293), Japan (14), U.S.A. (7), Mexico (6), Australia (4), Canada(4), Italy (3), Brazil (2) and 15 unknown origin accessions。 重要结论: 1. Four haplotypes were found in the 348accessions by the above sequence analysis: Hap-W, Hap-S1, Hap-S2, and Hap-N. 2. However, unlike previous researchers, we found the wild-type PFT sequence existed not only in resistant accessions but also insusceptible accessions such as Nonglin 67, Chuannong 42and Xiaoyan 54. 还是那句话,有这个gene,也不一定抗病。 3. Furthermore, five moderatelyresistant accessions, such as CA25, Ningyan 1 and Zhenmai 6 had mutant instead of wild-type PFT sequences. 4. For the 184 PFT negative accessions, only 102 accessionswere susceptible to FHB, while the remaining 82 accessions demonstrated moderateor high FHB resistance. 第三点和第四点说明没有这个PFT gene,也照样是抗病的。这点不一定跟PFT有关系,毕竟这些种植资源中有可能有其它的抗病基因。 以上的结果根据的就是这个图。说实话,这个图做为一个已克隆基因的验证结果,完全是不可以接受的(如果认为这个基因没有其它互作基因的话)。另外,这个图有一些细节也值得再深挖一些:比如说这个S2的haplotype 虽然呈现出非常感病,但是这种haplotype 却只有四个line;另外,Wild type 和S1 的haplotype 虽说在表型上有差异,但貌似也没有那么明显。(文中只给了平均数,没有Std和p value.但文章附加了原始数据,有兴趣的小伙伴可以下载)。 稍有遗憾的是,作者既然有这些line的origin,按照origin来分析一下结果应该会很有意思。还有,这300多个种质资源和NG文章中的40个材料有什么不同或者相同点呢(比如从origin和育种谱系来分析),为什么他们得到的结果是完全对应,而本文得到的结果却不一样(当然,从文章的题目可以看出,这篇文章的出发点和逻辑结构跟我的出发点不一样,所以可能也没打算在这方面多下功夫)。 根据以上结果,作者提出FHB抗性可能是多基因复合体: We speculate that wheat resistance to FHB is a multigenic complex trait, and PFT represents one of the genes to assist FHB resistance. Additional efforts are still needed to reveal the mechanisms of Fhb1 in FHB resistance. 最后,小编想说,虽然说后续的研究对NG那篇文章的结果都不能完美验证,但我还是对这篇文章充满敬意的,起码从那篇文章的结构和逻辑来说,确实是没有问题的。可是作者们也确实忽略或者说无意中错过了提出不确定性这样一个机会。我不知道如果这个研究在Supplementary Table 6 (40个line)的基础上再多选几个材料或者说没有那么“运气好”的话,发现几个有基因却不抗病,或者没基因也却抗病的情况,然后在文章中提出还有其它的基因也可能参与PFT复合体,是不是就更好一些。就像文中所提出的,Our discovery identifies a new type of durable plant resistance geneconferring quantitative disease resistance to plants against Fusarium species. 既然作者已经意识到这个gene是个quantitative resistance,提出还有其它基因参与抗性其实也算是顺理成章吧。不过要真是这种情况的话,文章是不是还能发在NG上就真不好说了。 总之,我们期待关于 Fhb1 更多更精彩的研究,有争议不可怕,解决争议的过程也就是走向真理的过程。
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2017年小麦赤霉病抗性遗传资源与基因定位研究进展
mashengwei 2018-2-8 21:51
2 7 本期作者:国家小麦产业技术体系 小麦赤霉病 ( Fusarium head blight , FHB ) 是 由 禾谷 镰刀菌引起 的世界性病害 ,在生产中造成 小麦 产量和品质的显著降低 。 小麦 感染赤霉病菌产生的 脱氧雪腐镰刀菌烯醇 ( DON )等毒素 严重危害人体健康,给小麦为主 的 食品安全带来很大 隐患 ( Pieczul et al ., 2015) 。 随着 全球气候变暖和秸秆还田 等耕作制度和方式的 改变 , 使我国 小麦赤霉病的发生区域有不断扩大的趋势,由温暖湿润的长江中下游麦区和东北春麦区逐渐向黄淮麦区和北方麦区等扩展 ( 李韬 等, 2016 ) 。 因此,赤霉病的防治 问题成为 我国乃至世界 小麦科学家 亟待解决的难题 。 国家 小麦产业技术体系针对我国 小麦生产 中 的 赤霉病 防治 问题, 从耕作栽培、优良品种、病情测报、药剂防治、产后加工等方面进行全产业链技术集成, 开发出 秸秆深埋、压低菌量,培育良种、增强抗性,准确测报、及时防治,改良药剂、提高防效,加工脱毒、粮食安全的小麦赤霉病综合防控技术 ,促进了 小麦产业的绿色发展 。 其中,收集和筛选赤霉病抗性资源,并在小麦育种中加以利用是提高寄主抗性水平防治赤霉病大流行的有效途径。本文重点总结 2016 年以来全世界范围内的赤霉病抗性遗传资源和抗性基因 /QTL 定位的主要研究进展,为有效促进我国的小麦抗赤霉病育种提供多样化的亲本资源信息 。 一、 苏麦 3 号及其衍生系来源的抗性资源 。 主要 包括 来自于地方品种台湾小麦 衍生 的苏麦 3 号、 宁 7840 、地方品种 望水白 等 (Bai et al ., 2003) ,和来自 日本的 NyuBai 、 西风小麦及其衍生的宁麦 9 号 (Mesterhazy, 1997; Ban, 2000; Rudd et al ., 2001) 。这些抗性遗传资源共同特点是含有 3B 染色体 抗赤霉病 基因 Fhb1 的主效 QTL 位点,对赤霉病抗性表现为 II 级抗扩展特性。 尤其是苏麦 3 号携带的 Fhb1 基因已经被全世界的小麦育种家积极利用于各类 小麦生态类型 的抗赤霉病育种中。 奥地利的育种家成功地将携带苏麦 3 号抗源的 Fhb1 位点的 DBC-480 硬粒小麦新品系,与法国的 2 个品种 Karur (KD) 和 Durobonus (DD) 以及奥地利品种 SZD1029K (SD) 杂交构建了 3 个 RIL 群体,通过 QTL 定位及赤霉病抗性鉴定,发现 3BS 染色体上 Fhb1 基因位点 表现 稳定的抗性,但是同时也发现 Fhb1 基因位点 的 抗性与株高 显著 负相关,不利于育种农艺性状的选择。 因此育种家 建议可以通过聚合 Fhb1 与 多个 其他位点的微效基因的办法来 消 除株高 降低 引起 的 赤霉病抗性下降 的负效应, 并且 在硬粒小麦的抗赤霉病育种取得 了 实质性的进步( Prat et al ., 2017 )。 苏麦 3 号的抗赤霉病基因除了 Fhb1 之外,还有其他染色体的基因 也 具有很大的 抗 赤霉病 效应。 另外一个 抗性较强 的 QTL ( Qfhs.ifa-5A )位于 5A 染色体 近着丝粒区域 ,但是因为 该位点 染色体 交换 频率较低 , 导致该 QTL 精细定位进展 缓慢 。最近,奥地利的一个团队利用 γ 射线辐照 诱变 的办法,获得一系列 5AS 不同长度缺失的 突变体,成功地在 5AS 近着丝粒区建立起一个标记密度高达 0.77 Mb/cR 的高分辨率图谱,为 5AS 的精细定位打下了坚实的基础( Buerstmayr et al .,2017 )。 二 、 其他来源的抗性种质 加拿大的 Kage et al . (2017) 研究小组报道 从 武汉 1 号 的 主效 FHB QTL-2DL , 分离到一个次生代谢途径的基因 TaACT ,该基因编码 胍丁胺桂皮酰转移酶 ,侧翼 SSR 标记为 WMC245 和 GWM608 , 通过携带与不含 FHB QTL-2DL 近等基因系的表型鉴定,证实该位点 具有很好的 抗小穗 扩展特性, 并通过病毒介导的基因沉默和转基因互补拟南芥实验证实 TaACT 基因能够增强小麦的赤霉病抗性 。 Wang et al .(2017) 报道从美国、加拿大和 CIMMYT 收集的 170 个春性小麦品种鉴定出 14 份在多环境下表现 赤霉病 抗性稳定的材料,这些材料包括 OTIS 、 IDO851 、 IDO686 、 IDO671 、 WHITEBIRD 、 610750 、 UC1603 、 UC1642 、 VIDA 、 MT0415 、 9232 、 9245 、 9241 和 9248 。 通过全基因组关联分析发现这些材料没有苏麦 3 号背景,主效 QTL 位点主要分布在 1B 、 2B 、 4B 、 5A 、 5B 和 6A 上 ,其中 5B 染色体上的抗性位点被认为 是 区别于以往报道的新位点。 日本东京大学的 Nishio 研究团队从日本最新培育的一个硬红冬麦品种 Yumechikara 中分离到一个解释表型变异率达到 36.4% 的稳定 QTL ,该 QTL 位于 1BS 染色体上,并通过 5 年的田间表型鉴定证实该种质对赤霉病抗性非常稳定, 同时 该种质具有抗黄矮病、极强的抗寒性和优异的面包品质。 Yumechikara 同时 拥有 1BS 上的抗赤霉病主效 QTL 和其余几个优异性状,是一个值得引进和利用的优异种质资源( Nishio et al ., 2016 )。 CIMMYT 的 Pawan Singh 研究团队 利用 来自上海 3 号赤霉病抗源的 Soru#1 品系,构建 DH 系,在 2 年 3 个环境下进行了 QTL 定位研究,结果验证了来自上海 3 号的 2DLc 的主效 QTL ,可 解释 15-22% 的表型变异,并发现该位点 的赤霉病 抗性与株高和抽穗期具有显著的相关性 ,他们解释了该位点抗性为 I 型抗赤霉病菌侵染类型( He et al ., 2016 ) 。 海盐种( Haiyanzhong )是中国的一个小麦地方品种,已经报道对赤霉病表现很好的 II 型抗扩展特性 , 美国堪萨斯州立大学 柏贵华教授研究团队对其赤霉病抗性进行了 QTL 定位研究,发现 具有 最大效应的 QTL 定位于小麦 5AS 染色体上, 并排除了 海盐种 携带 3BS 的 Fhb1 位点 的 可能 性 。此外,除了 在海盐种中 发现存在已经报道的 Fhb2 、 Fhb4 和 Fhb5 位点外,还发现在染色体 2B 、 3B 和 4D 上存在多个 微效 的 QTL , 表明 其抗性同时受多个微效 QTL 所控制。 他们 还 进一步 利用 KASP 技术开发出该位点的 SNP 检测标记,便于育种家利用该种质进行分子标记辅助选育( Cai et al ., 2016 )。 硬粒小麦的赤霉病抗性资源相对较少,其中来自野生二粒小麦的一个中抗赤霉病的 QTL Qfhs.ndsu-3AS 受到小麦育种家的关注。来自美国北 Dakota 州立大学的研究小组进一步对该位点进行了定位,将 Qfhs.ndsu-3AS 定位于 3AS 标记 Xwgc501 - Xwgc510 之间 5.2cM 区间内 , 便于更有目标地利用该座位改良硬粒小麦( Zhu et al ., 2016 )。 三 、来自野生近缘植物的抗性资源研究进展 Liu et al .(2015) 报道普通小麦和中间偃麦草的衍生系 PI 67253 在 多年多点 环境中 均 表现出高抗赤霉病特性 。 Li et al .(2017) 进一步利用 PI 67253 与感病品种构建的 F 2 和 F 2:3 家系分离群体进行了 QTL 定位研究,检测到 2 个主效 QTL ( Qfhs-2B, Qfhs-3B ),其中 Qfhs-2B 连锁的 2 个侧翼标记为 Xbarc55-2B 和 Xbarc1155-2B, 对 赤霉病的 小穗 扩展 解释 高 达 11.6% 表型变异 , Qfhs-3B 侧翼标记为 Xwmc54-3B 和 Xgwm566-3B, 解释 10% 以上的表型变异,并且不同于已经报道的 Fhb1 , 因此 认为 来自中间偃麦草的 PI 67253 是一个新的有利用前景的赤霉病抗源,值得我们的关注。 Dai et al .(2017) 利用 6 倍体小黑麦(基因组为 AABBRR )和 6 倍体小偃麦(基因组为 AABBEE )杂交获得一个稳定遗传的杂交后代 RE21 ,通过细胞遗传学和分子标记鉴定确定其染色体组成为 7 对 A 染色体、 7 对 B 染色体、 3 对 R 染色体( 4R 、 6R 和 7R )以及 4 对 E 染色体( 1E 、 2E 、 3E 和 5E ),表型鉴定 为 对赤霉病高抗,并推测其抗性来源于长穗偃麦草的 1E 染色体。该研究有效地引入野生种偃麦草的抗性基因,为今后的小麦赤霉病抗性育种提供了有价值的遗传资源。 Ceoloni et al .(2017) 报道 通过 以辐照方法创制的 7DS · 7DL/7el1L 易位系材料 T4( 对赤霉病感病 ) 为桥梁材料, 与 鉴定 出 具有稳定抗性的中国春 7E/7D 代换系为供体相互杂交,在后代中鉴定出 7el1L 片段发生重组的个体,从而导入 了 长穗偃麦草 7E 染色体上的新抗性基因 。并且 对该种质进行了综合抗性和产量因子的鉴定,发现新创制的材料兼抗赤霉病、 叶锈病(携带 Lr19 抗性基因),同时表现出可以提高小穗育性的产量性状优势。 此外, 一粒小麦、 栽培 二粒小麦、波兰小麦 ( 包含卡姆小麦 ) 、斯卑尔 脱 小麦 等 作为小麦改良的二级基因源,它们的赤霉病抗性备受关注。来自波兰的研究团队采用人工接种的方法比较了以上二级基因源与普通小麦的赤霉病抗性,最后发现 斯卑尔脱小麦受赤霉病的侵染最轻,而且病穗籽粒毒素 DON 含量最低, 相反,波兰小麦、 以及 卡姆小麦对赤霉病表现为高感。 因此 在利用 二级基因源 改良小麦赤霉病 抗性 时 应该优先考虑斯卑尔脱小麦 ( Wiwart et al .,2016 ) 。 四 、 Fhb1 基因克隆与分子标记辅助选择 目前在小麦的 21 条染色体定位的 QTL 已经超过 250 个,可是大多数是微效基因,因此 使 赤霉病抗性基因克隆 进展较慢 (Jiang et al ., 2017) 。一个最受关注且来源于苏麦 3 号的主效 QTL Fhb1 首先被美国堪萨斯州立大学的 B. S. Gill 团队所克隆。他们通过图位克隆获得小麦 3BS 染色体上的编码 穿孔毒素 凝集素的基因 (pore-forming toxin-like , PFT ) ,并通过突变体分析、基因沉默和转基因过量表达实验证实 PFT 就是 3BS 上的赤霉病抗性基因( Rawat et al ., 2016 )。 可是, 在 PFT 克隆的文章发表之后,国际同行对该基因是否是真的赤霉病抗性基因提出质疑。在 2017 年奥地利举办的第 13 届国际小麦遗传学会上,特邀美国 堪萨斯州立大学的 柏 贵 华教授、南京农业大学马正强教授和奥地利 维也纳 自然资源 与 生命 科学大学 ( BOKU )的 Steiner 教授 分别 在大会 上发表了自己对 Fhb1 基因克隆的看法( 13th IWGS 2017 , Austria )。 我国南京农业大学的马正强教授团队长期致力于赤霉病的抗性 QTL 定位和基因克隆研究,他们团队从 江苏溧阳的 地方品种 望水 白中分离和鉴定了 Fhb1 主效 QTL 位点,已经获得候选基因,结果待发表( Jia et al ., 2017 )。他们通 过 4 个证据认为 PFT 基因还不足以完全解释苏麦 3 号和 望水 白的赤霉病抗性。首先是 PFT 基因从序列上在感病品种 PH691 和抗病品种苏麦 3 号、 望水 白 中 完全一致 ; 其次在南大 2419 和 望水 白的 RIL 群体中分离到只保留 PFT 基因座位的交换单株表现为感病类型 ; 再者关联分析表明 151 个品种中 44 个含有 PFT 基因,但是只有 12 个品种鉴定具有赤霉病抗性 ; 最后发现接种前后 PFT 基因 在抗性亲本 望水 白 和 感病亲本南大 2419 中的表达水平都是很低的。 美国堪萨斯州立大学的柏贵华教授则认为 PFT 座位侧翼的 H i s 基因( histidine-rich calcium-binding protein ,又名 His 基因或者 TaHRC )是 Fhb1 的候选基因,他们通过对广泛收集的抗性资源序列分析,发现抗性材料中的 H i s 基因普遍存在 750bp 的缺失,并发现发生 His 基因缺失的种质仅分布于中国华南地区和日本的一些材料中。柏贵华教授团队进一步采用 RNA 干扰和基因编辑实验证实 His 基因是 Fhb1 的抗性基因。 最近,中国农科院作科所 何中虎研究员团队 利用以上标记开展了中国小麦品种抗赤霉病基因 Fhb1 的鉴定与溯源研究,他们通过分析 229 份小麦品种 Fhb1 区段内 PFT 、 HC (HCBT-like defense response protein) 和 His 基因的多样性与赤霉病抗性的关系, 利用 基因检测和系谱分析 发现 中国小麦品种所含 Fhb1 至少有两个来源,分 别来 自苏麦 3 号和宁麦 9 号,并以后者为主, 也 证实 His 基因的检测与赤霉病的抗性最为一致,并开发出有效诊断的分子标记 PFT-CAPS 和 His-InDel (朱展望 等 , 已接收 )。 结语 总结 201 6-2017 年度在赤霉病抗性种质鉴定 、 QTL 定位和基因克隆 方面的 工作,可以发现 当前世界范围 内 的小麦科学家 仍然是以苏麦 3 号为主要抗源开展小麦品种改良和基因克隆,利用抗源 相对比较 单一。同时 也看到新的小麦抗性 资源 逐渐被鉴定和利用的乐观形势,比如美国 PI277012 种质是六倍体小麦,田间鉴定抗性优于苏麦 3 号,研究发现 2 个主效 QTL 在小麦的 5AS 和 5AL 上,通过回交转育发现可以显著提高受体小麦的赤霉病抗性 ( Chu et al ., 2011 ) 。还有本文介绍的日本品种 Yumechikara (抗性位点在 1BS 上)、小麦野生近缘物种导入的 7DS · 7DL/7el1L 材料(携带长穗偃麦草 7E 片段)、小麦 - 黑麦 - 偃麦草 3 属杂交后代 RE21 (抗性来自偃麦草 1E )这些种质应该足够引起我们的重视和引进。 欢迎关注 “ 小麦研究联盟 ”, 了解小麦新进展 投稿、转载、合作以及信息分布等请联系: wheatgenome
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2018年第一周小麦文献推荐(1.7)
mashengwei 2018-1-6 15:38
2018年第一周小麦文献推荐(1.7) 本期作者 麦萌 小麦生信联盟 Hi,大家好!欢迎来到一周一次的小麦文献推荐。今天是2018年的第一次推荐,在此有必要对此简单的介绍下。首先,我们周一至周六会解读一些文献,但是限于我们主编的背景知识,在选择文献上可能具有一定的偏好性,再加上现在小麦研究越来越热门,发表的文章也会越来越多,研究的质量也会越来越高,所以总是会漏掉一些文献,这些漏掉的文献不代表不重要。为了弥补这个遗憾,我们特别在周末汇总这一周和小麦相关的文献,供大家浏览和参考,这些文献有些可能会被我们解读,有些则不会。每一篇文献会有题目,作者,发表杂志以及摘要信息,供大家决定是否需要进一步阅读。 想要特别声明一点,无论是我们推荐的文章还是我们做过导读的文章,都不能代替您亲自读文章,不能代表您对这篇文章的思考。同样一篇文献,每个人get到的点一定不一样。一个人多次阅读文章,可能每次引起的思考也会不同。 突然想起来颜宁说过她在国外上课时,老师都会给一些经典的生物文献,并且要求找出文献的问题。这种训练教会她学会质疑。科学没有挑战权威的质疑精神,就不可能有创新。同样的,这种讨论也应该存在于导师指导过程中,学生也要敢于向导师说出自己的想法,也许会由于思虑不周或欠缺相关背景知识而显得幼稚,或者观点错误,这些都没关系,立即改正过来就行。当然了,实际情况可能要复杂,导师也不是你想要和他讨论他就能和你讨论的。导师也是一个普通人,每个人都有自己的风格。 说的多了,我们正式开始我们的文献推荐。 1 Genetic diversity and virulence of wheat and barley strains of Xanthomonas translucens from the Upper Midwestern United States Bacterial leaf streak (BLS) of wheat and barley, caused by Xanthomonas translucens pv. undulosa and Xanthomonas translucens pv. translucens, has been of growing concern in small grains production in the Upper Midwestern United States. To optimize disease resistance breeding, a greater awareness is needed of the pathovars and genetic diversity within the pathogens causing BLS in the region. Multilocus sequencing typing (MLST) and analysis (MLSA) of four common housekeeping genes (rpoD, dnaK, fyuA and gyrB) was used to evaluate the genetic diversity of 82 strains of X. translucens isolated between 2006 and 2013 from wheat, barley, rye and intermediate wheatgrass. In addition, in planta disease assays were conducted on 75 strains to measure relative virulence in wheat and barley. All strains were determined by MLSA to be related to X. translucens pv. undulosa and X. translucens pv. translucens. Clustering of strains based on Bayesian, network, and minimum spanning trees correlated with relative virulence levels in inoculated wheat and barley. Thus, phylogeny based on rpoD, dnaK, fyuA and gyrB correlated with host of isolation and was an effective means for predicting virulence of strains belonging to X. translucens pv. translucens and X. translucens pv. undulosa. 2 Analysis of contributors to grain yield in wheat at the individual quantitative trait locus level In wheat, strong genetic correlations have been found between grain yield (GY) and tiller number per plant (TN), fertile spikelet number per spike (FSN), kernel number per spike (KN) and thousand-kernel weight (TKW). To investigate their genetic relationships at the individual quantitative trait locus (QTL) level, we performed both normal and multivariate conditional QTL analysis based on two recombinant inbred lines (RILs) populations. A total of 79 and 48 normal QTLs were identified in the International Triticeae Mapping Initiative (ITMI)/SHW-L1 9 Chuanmai 32 (SC) populations, respectively, as well as 55 and 35 conditional QTLs. Thirty-two QTL clusters in the ITMI population and 18 QTL clusters in the SC population explained 0.9%– 46.2% of phenotypic variance for two to eight traits. A comparison between the normal and conditional QTL mapping analyses indicated that FSN made the smallest contribution to GY among the four GY components that were considered at the QTL level. The effects of TN, KN and TKW on GY were stronger at the QTL level. 3 Genome-Wide Association Mapping of Loci for Resistance to Stripe Rust in North American Elite Spring Wheat Germplasm Stripe rust, caused by Puccinia striiformis f. sp. tritici, is a major yield-limiting foliar disease of wheat (Triticum aestivum) worldwide. In this study, the genetic variability of elite spring wheat germplasm from North America was investigated to characterize the genetic basis of effective all-stage and adult plant resistance (APR) to stripe rust. A genome-wide association study was conducted using 237 elite spring wheat lines genotyped with an Illumina Infinium 90K single-nucleotide polymorphism array. All-stage resistance was evaluated at seedling stage in controlled conditions and field evaluations were conducted under natural disease pressure in eight environments across Washington State. High heritability estimates and correlations between infection type and severity were observed. Ten loci for race-specific all-stage resistance were confirmed from previous mapping studies. Three potentially new loci associated with race-specific all-stage resistance were identified on chromosomes 1D, 2A, and 5A. For APR, 11 highly significant quantitative trait loci (QTL) (false discovery rate 0.01) were identified, of which 3 QTL on chromosomes 3A, 5D, and 7A are reported for the first time. The QTL identified in this study can be used to enrich the current gene pool and improve the diversity of resistance to stripe rust disease. 4 Fluorescence in situ hybridization karyotyping reveals the presence of two distinct genomes in the taxon Aegilops tauschii The distribution of sites hybridizing to the two probes oligo-pTa-535 and (CTT)10 split the Ae. tauschii accessions into two clades, designated Dt and Ds, which corresponded perfectly with a previously assembled phylogeny based on marker genotype. The Dt cluster was populated exclusively by ssp. tauschii accessions, while the Ds cluster harbored both ssp. strangulata and morphologically intermediate accessions. As a result, it is proposed that Ae. tauschii ssp. tauschii is restricted to carriers of the Dt karyotype: their spikelets are regularly spaced along the rachis, at least in the central portion of their spike. Accessions classified as Ae. tauschii ssp. strangulata carry the Ds karyotype; their spikelets are irregularly spaced. Based on this criterion, forms formerly classified as ssp. tauschii var. meyeri have been re-designated ssp. strangulata var. meyeri . According to the reworking of the taxon, the bread wheat D genome was most probably donated by ssp. strangulata var. meyeri . Chromosomal differentiation reveals intra-species taxon of Ae. tauschii . Ae. tauschii ssp. tauschii has more distant relationship with breed wheat than ssp. strangulata and can be used for breeding improving effectively. 5 Asymmetrical changes of gene expression, small RNAs and chromatin in two resynthesized wheat allotetraploids Polyploidy occurs in some animals and all flowering plants including important crops such as wheat. The consequences of polyploidy on crops remain elusive partly because their progenitors are unknown. Using two resynthesized wheat allotetraploids SlSlAA and AADD with known diploid progenitors, we analyzed mRNA and small RNA transcriptomes in the endosperm, compared transcriptomes between endosperm and root in AADD, and examined chromatin changes in the allotetraploids. In the endosperm, there were more nonadditively expressed genes in SlSlAA than in AADD. In AADD, nonadditively expressed genes were developmentally regulated, and the majority (62-70%) were repressed. The repressed genes in AADD included a group of histone methyltransferase gene homologs, which correlated with reduced histone H3K9me2 levels and activation of various transposable elements in AADD. In SlSlAA, there was a tendency of expression dominance of Sl over A homoeologs, but the histone methyltransferase gene homologs were additively expressed, correlating with insignificant changes in histone H3K9me2 levels. Moreover, more 24-nt small inferring RNAs (siRNAs) in the A subgenome were disrupted in AADD than in SlSlAA, which were associated with expression changes of siRNA-associated genes. Our results indicate that asymmetrical changes in siRNAs, chromatin modifications, transposons, and gene expression coincide with unstable AADD genomes and stable SlSlAA genomes, which could help explain evolutionary trajectories of wheat allotetraploids formed by different progenitors. 6 Genetic characterization of type II Fusarium head blight resistance derived from transgressive segregation in a cross between Eastern and Western Canadian spring wheat Fusarium head blight (FHB) caused by Fusarium graminearum is a devastating disease affecting global wheat production, causing significant losses to yield and grain quality. The Eastern Canadian line FL62R1 was developed using a systemic breeding approach and boasts high levels of FHB resistance with good yield, desirable agronomics, and end-use quality traits. The objective of this study was to identify genetic determinants of type II resistance in a cross between FL62R1 and cv. Stettler, a Canada Western Red Spring variety rated moderately susceptible to FHB. Although neither parent displayed strong resistance to FHB spread within spikes following point inoculation (type II resistance) in greenhouses, strong type II resistance was observed in a large number of progeny, including 6% with resistance comparable to the best check line, Sumai 3. Quantitative trait locus (QTL) mapping identified a locus from chromosome 2BL of Stettler which provides Sumai 3 level type II resistance when combined with favorable FHB resistance QTLs with minor effects from FL62R1. This study provides insight into transgressive segregation for FHB, which despite its importance is poorly understood, rare, and difficult to predict. It also begins to dissect the genetic architecture of FHB resistance in wheat derived from the systemic breeding approach. 7 Brassinosteroids Modulate Meristem Fate and Differentiation of Unique Inflorescence Morphology in Setaria viridis(狗尾草,禾本科) Inflorescence architecture is a key determinant of yield potential in many crops and is patterned by the organization and developmental fate of axillary meristems. In cereals, flowers and grain are borne from spikelets, which differentiate in the final iteration of axillary meristem branching. In Setaria spp., inflorescence branches terminate in either a spikelet or a sterile bristle, and these structures appear to be paired. In this work, we leverage Setaria viridis to investigate a role for the phytohormones brassinosteroids (BRs) in specifying bristle identity and maintaining spikelet meristem determinacy. We report the molecular identification and characterization of the Bristleless 1 (Bsl1) locus in S. viridis, which encodes a rate-limiting enzyme in BR biosynthesis. Loss-of-function bsl1 mutants fail to initiate a bristle identity program, resulting in homeotic conversion of bristles to spikelets. In addition, spikelet meristem determinacy is altered in the mutants, which produce two florets per spikelet instead of one. Both of these phenotypes provide avenues for enhanced grain production in cereal crops. Our results indicate that the spatiotemporal restriction of BR biosynthesis at boundary domains influences meristem fate decisions during inflorescence development. The bsl1 mutants provide insight into the molecular basis underlying morphological variation in inflorescence architecture. 8 Critical and speculative review of the roles of multi-protein complexes instarch biosynthesis in cereals Starch accounts for the majority of edible carbohydrate resources generated through photosynthesis. Amylopectin is the major component of starch and is one of highest-molecular-weight biopolymers. Rapid and systematic synthesis of frequently branched hydro-insoluble amylopectin and efficient accumulation into amyloplasts of cereal endosperm is crucial. The functions of multiple starch biosynthetic enzymes, including elongation, branching, and debranching enzymes, must be temporally and spatially coordinated. Accordingly, direct evidence of protein-protein interactions of starch biosynthetic enzymes were first discovered in developing wheat endosperm in 2004, and they have since been shown in the developing seeds of other cereals. This review article describes structural characteristics of starches as well as similarities and differences in protein complex formation among different plant species and among mutant plants that are deficient in specific starch biosynthetic enzymes. In addition, evidence for protein complexes that are involved in the initiation stages of starch biosynthesis is summarized. Finally, we discuss the significance of protein complexes and describe new methods that may elucidate the mechanisms and roles of starch biosynthetic enzyme complexes. 9 Developmental responses of bread wheat to changes in ambient temperature following deletion of a locus that includes FLOWERING LOCUS T1 FLOWERING LOCUS T ( FT ) is a central integrator of environmental signals that regulates the timing of vegetative to reproductive transition in flowering plants. In model plants, these environmental signals have been shown to include photoperiod, vernalization and ambient temperature pathways, whilst in crop species the integration of the ambient temperature pathway remains less well understood. In hexaploid wheat, at least 5 FT-like genes have been identified, each with a copy on the A, B and D genomes. Here we report the characterization of FT-B1 through analysis of FT-B1 null and over-expression genotypes under different ambient temperature conditions. This analysis has identified that the FT-B1 alleles perform differently under diverse environmental conditions; most notably the FT-B1 null produces an increase in spikelet and tiller number when grown at lower temperature conditions. Additionally, absence of FT-B1 facilitates more rapid germination under both light and dark conditions. These results provide an opportunity to understand the FT-dependent pathways that underpin key responses of wheat development to changes in ambient temperature. This is particularly important for wheat, for which development and grain productivity is sensitive to changes in temperature. 10 On the Origin of the Non-brittle Rachis Trait of Domesticated Einkorn Wheat Einkorn and emmer wheat together with barley were among the first cereals domesticated by humans more than 10,000 years ago, long before durum or bread wheat originated. Domesticated einkorn wheat differs from its wild progenitor in basic morphological characters such as the grain dispersal system. This study identified the Non-brittle rachis 1 ( btr1 ) and Non-brittle rachis 2 ( btr2 ) in einkorn as homologous to barley. Re-sequencing of the Btr1 and Btr2 in a collection of 53 lines showed that a single non-synonymous amino acid substitution (alanine to threonine) at position 119 at btr1 , is responsible for the non-brittle rachis trait in domesticated einkorn. Tracing this haplotype variation back to wild einkorn samples provides further evidence that the einkorn progenitor came from the Northern Levant. We show that the geographical origin of domesticated haplotype coincides with the non-brittle domesticated barley haplotypes, which suggest the non-brittle rachis phenotypes of einkorn and barley were fixed in same geographic area in today’s South-east Turkey. 11 Pyramiding of transgenic Pm3 alleles in wheat results in improved powdery mildew resistance in the field Allelic Pm3 resistance genes of wheat confer race-specific resistance to powdery mildew ( Blumeria graminis f. sp. tritici , Bgt ) and encode nucleotide-binding domain, leucine-rich repeat (NLR) receptors. Transgenic wheat lines overexpressing alleles Pm3a, b, c, d, f, and g have previously been generated by transformation of cultivar Bobwhite and tested in field trials, revealing varying degrees of powdery mildew resistance conferred by the transgenes. Here, we tested four transgenic lines each carrying two pyramided Pm3 alleles, which were generated by crossbreeding of lines transformed with single Pm3 alleles. All four allele-pyramided lines showed strongly improved powdery mildew resistance in the field compared to their parental lines. The improved resistance results from the two effects of enhanced total transgene expression levels and allele-specificity combinations. In contrast to leaf segment tests on greenhouse-grown seedlings, no allelic suppression was observed in the field. Plant development and yield scores of the pyramided lines were similar to the mean scores of the corresponding parental lines, and thus, the allele pyramiding did not cause any negative effects. On the contrary, in pyramided line, Pm3b × Pm3f normal plant development was restored compared to the delayed development and reduced seed set of parental line Pm3f. Allele-specific RT qPCR revealed additive transgene expression levels of the two Pm3 alleles in the pyramided lines. A positive correlation between total transgene expression level and powdery mildew field resistance was observed. In summary, allele pyramiding of Pm3 transgenes proved to be successful in enhancing powdery mildew field resistance. 12 Chemical hybridizing agent SQ-1-induced male sterility in Triticum aestivum L.: a comparative analysis of the anther proteome We performed proteomic analyses using the wheat Triticum aestivum L.to identify those proteins involved in physiological male sterility (PHYMS) induced by the chemical hybridizing agent CHA SQ-1. A total of 103 differentially expressed proteins were found by 2D–PAGE and subsequently identified by MALDI-TOF/TOF MS/MS. In general, these proteins had obvious functional tendencies implicated in carbohydrate metabolism, oxidative stress and resistance, protein metabolism, photosynthesis, and cytoskeleton and cell structure. In combination with phenotypic, tissue section, and bioinformatics analyses, the identified differentially expressed proteins revealed a complex network behind the regulation of PHYMS and pollen development. Accordingly, we constructed a protein network of male sterility in wheat, drawing relationships between the 103 differentially expressed proteins and their annotated biological pathways. To further validate our proposed protein network, we determined relevant physiological values and performed real-time PCR assays. Our proteomics based approach has enabled us to identify certain tendencies in PHYMS anthers. Anomalies in carbohydrate metabolism and oxidative stress, together with premature tapetum degradation, may be the cause behind carbohydrate starvation and male sterility in CHA SQ-1 treated plants. Here, we provide important insight into the mechanisms underlying CHA SQ-1-induced male sterility. Our findings have practical implications for the application of hybrid breeding in wheat. 13 Effects of Three Parastagonospora nodorum Necrotrophic Effectors on Spring Wheat under Norwegian Field Conditions The wheat (Triticum aestivum L.) disease Septoria nodorum blotch (SNB) is caused bythe necrotrophic fungus Parastagonospora nodorum (Berk.) Quaedvlieg, Verkley Crousand causes significant yield and quality losses in several wheat growing regions. Theresistance mechanisms are quantitative and progress in resistance breeding has beenslow. However, gene-for-gene interactions involving necrotrophic effectors (NEs) andsensitivity genes (Snn) are involved, providing hope for more effective breeding. Althoughthe interactions are significant determinants of seedling SNB susceptibility, their role inadult plant leaf blotch resistance in the field is less understood. In this study, the frequencyof SnTox genes was investigated in 62 P.nodorum isolates collected in Norway. A panel of Norwegian and international spring wheat lines and cultivars was screened under natural SNB infection in a mist-irrigated field nurseryacross 7 yr. The lines were infiltrated in the greenhouse with the purified NEs SnToxA,SnTox1, and SnTox3, and the prevalence of corresponding sensitivity was investigated, aswell as correlation between NE sensitivity and resistance level in the field. The frequencies of SnToxA, SnTox1, and SnTox3 in the isolates were 0.69, 0.53 and 0.76, respectively.Sensitivity to SnToxA, SnTox1, and SnTox3 was present in 45, 12, and 55% of the plant material. Sensitivity to SnToxA was associated with significantly higher disease severity in the field than insensitivity. This indicates that elimination of SnToxA sensitivity in the breeding material by effector infiltrations or marker-assisted selection can be an effective way to increase field resistance to SNB. 14 Proteomic analysis of low-molecular-weight glutenin subunits and relationship with their genes in a common wheat variety Although many studies on low-molecular-weight glutenin subunit (LMW-GS) function have been reported, a comprehensive comparison between specific genes and their protein product is still lacking. This study aimed to link the 43 genes isolated from the Korean wheat variety “Jokyoung” in the authors’ previous study to their protein products. Proteins were separated using two-dimensional gel electrophoresis (2-DGE) and identified by tandem mass spectrometry (MS/MS) at the gene haplotype level. Using MS/MS analysis of 17 protein spots, two spots were identified in the Glu-A3 locus and the corresponding haplotype was GluA3-13(Glu-A3c). Six spots were identified in the Glu-B3 locus and the corresponding haplotypes were GluB3-33 and GluB3-43 (Glu-B3h). Eight spots were identified in the Glu-D3 locus and the corresponding haplotypes were GluD3-11, GluD3-21, GluD3-31, GluD3-5, and GluD3-6 (Glu-D3a), and one spot was contaminated with gamma gliadin. Phylogenetic analysis and alignment of nucleotide and amino acid sequences assigned 35 of the 43 genes to seven haplotypes: GluA3-13, GluB3-43, GluD3-11, GluD3-21, GluD3-31, GluD3-42, and GluD3-5. Taken together, except for GluB3-33 and GluD3-6, which were not isolated, linking of each gene to the corresponding protein products at the gene haplotype level was accomplished using proteomic tools and phylogenetic analysis. 欢迎关注“小麦研究联盟”
个人分类: 文献推荐|3220 次阅读|0 个评论
带赤霉病麦种注意用药处理
tjm9518 2010-9-16 10:35
上年度小麦赤霉病发生重,种子带菌容易引起苗枯 盱眙县一农资销售商来电话说,上年度他供种由农户繁殖了数百万斤烟农19种子,前一段时间他简单地做了一下发芽试验,麦种3天发芽率在90%以上,但绝大部分种子上长出了一层白霉。他问,麦种为什么会长霉,这些种子能不能作种用。据了解,今年当地赤霉病发生重,上述烟农19繁种田赤霉病发生也较重,种子清选时清除了大量发红的赤霉病瘪粒。做种子发芽试验时只是简单地将100粒种子压在两块砖之间,放入盛有浅水层(水深3厘米左右,不淹第一块砖)的盆中。先后做过两次试验,都发生种子长白霉现象。 种子可能带赤霉病菌 从反映的情况看,上述麦种很可能带有大量的赤霉病孢子,在发芽试验期由于湿度较大、温度较高,病孢子迅速萌发,长出菌丝,形成霉层。进一步观察,随着菌丝生长发育,如果霉层颜色逐渐发红,可以基本断定麦种上长霉由种子带赤霉病菌引起。如果要确诊,可以到当地植保部门镜检。 带菌种子可以利用 赤霉病在小麦各生育期均能发生。苗期形成苗枯,成株期形成茎基腐烂和穗枯,以穗枯危害最重,常是1~2个小穗被害,有时很多小穗或整穗受害。被害小穗颖壳的合缝处常生出一层明显的粉红色霉层(分生孢子)。籽粒发病后皱缩干瘪,变为苍白色或紫红色,有时籽粒表面有粉红色霉层。 小麦赤霉病是比较典型的气候型病害,抽穗扬花期遇阴雨天气或多雾天气容易发病,否则不容易发病。在江苏、安徽等广大麦区,田间赤霉病菌源数量大,菌源不是赤霉病发生的限制因素。播种带赤霉病菌的麦种,虽然在一定程度上增加了田间菌源数量,但并不是赤霉病发生的决定性因素。 受生育期推迟、麦收前后遇阴雨天气等影响,今年江苏、安徽等地小麦繁种数量减少、种子质量下降,特别是适合沿淮等地种植的一些白皮麦品种,赤霉病发生较重,种子产量更少,导致秋播小麦用种供应紧张。在这种情况下,生产上可以考虑使用带赤霉病种子。商品麦供应不足时,农户可以考虑使用自繁麦种。 种子处理预防苗枯 使用带赤霉病菌麦种时,应事先检查其发芽率。今年小麦生育期推迟,很多田块小麦因急于腾茬等原因而抢收,种子灌浆不充实;赤霉病发生较重的田块,小麦穗轴受赤霉病危害后变褐坏死,会使上部没有发病的小穗因得不到水分而早枯,灌浆不足。这些都会在一定程度上影响种子的发芽率和发芽势,最终影响成苗。普通农户可以采用一些简单的检测方法,大致测定麦种发芽率,一般要求3天内发芽率达80%以上。种子发芽率较低时,应考虑相应增加播种量,或者不予使用。 种子带赤霉病菌,容易形成苗枯。带菌种子播种后,病孢子萌发侵入幼苗,会使根鞘及芽鞘呈黄褐色水浸状腐烂,地上部叶色发黄,重者幼苗未出土即死亡。特别是在播种后温度较高、土壤湿度较大的情况下,赤霉病更容易发生和危害,加重死苗。生产上应注意用药进行种子处理,杀灭麦种上的病菌。 土壤带菌量大时,麦苗茎基部易受害,变褐腐烂,严重时整株枯死。今年,江苏、安徽等省除沿淮地区赤霉病发生严重外,其他地区赤霉病发生也比较严重,田间菌源充足。特别是我省很多地方麦草还田面积大,麦草腐烂不良的田块,到小麦生长季节土壤带菌数量往往较大,这在一定程度上增加了小麦受赤霉病危害发生茎基部腐烂的威胁。通过种子处理和苗期用药预防,有利于减轻危害。 用多菌灵进行种子处理,是预防赤霉病危害造成小麦芽腐和苗枯经济有效的措施。可以按每100公斤种子用50%多菌灵可湿性粉剂200~400 克 加水喷拌麦种。另外还可以使用苯醚甲环唑、戊唑醇等药剂进行种子处理。这类药剂杀菌谱广,不仅对赤霉病有较好的防效,还能兼防苗期纹枯病,对腥黑穗病、散黑穗病、根腐病等病害也有良好防效。近年来我省各地小麦纹枯病发生较重,沿淮、沿海地区一些地方小麦根腐 病、散黑穗病发生较重,沿江苏南等地多个县市发现在腥黑穗病发生。这些地区可以优先使用苯醚甲环唑、戊唑醇等药剂进行种子处理。另外可以在春季结合防治纹枯病,使用苯甲丙环唑、戊唑醇等药兼防赤霉病引起的茎基部腐烂。(水清)
个人分类: 植保问题|8014 次阅读|0 个评论

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