Brassinosteroid signaling positively regulates abscisic acid biosynthesis in response to chilling stress in tomato

S An, Y Liu, K Sang, T Wang, J Yu, Y Zhou, X Xia

Journal of Integrative Plant Biology

Brassinosteroids (BRs) and abscisic acid (ABA) are essential regulators of plant growth and stress tolerance. Although the antagonistic interaction of BRs and ABA is proposed to ensure the balance between growth and defense in model plants, the crosstalk between BRs and ABA in response to chilling in tomato (Solanum lycopersicum), a warm‐climate horticultural crop, is unclear. Here, we determined that overexpression of the BR biosynthesis gene DWARF (DWF) or the key BR signaling gene BRASSINAZOLE‐RESISTANT1 (BZR1) increases ABA levels in response to chilling stress via positively regulating the expression of the ABA biosynthesis gene 9‐CIS‐EPOXYCAROTENOID DIOXYGENASE1 (NCED1). BR‐induced chilling tolerance was mostly dependent on ABA biosynthesis. Chilling stress or high BR levels decreased the abundance of BRASSINOSTEROID‐INSENSITIVE2 (BIN2), a negative regulator of BR signaling. Moreover, we observed that chilling stress increases BR levels and results in the accumulation of BZR1. BIN2 negatively regulated both the accumulation of BZR1 protein and chilling tolerance by suppressing ABA biosynthesis. Our results demonstrate that BR signaling positively regulates chilling tolerance via ABA biosynthesis in tomato. The study has implications in production of warm‐climate crops in horticulture.

BRs和脱落酸（ABA）是植物生长和抗逆性的重要调节因子。尽管BRs和ABA的拮抗作用被提出来确保模式植物的生长和防御之间的平衡，但BRs和ABA在番茄（Solanum lycopersicum）（一种温暖气候的园艺作物）中对寒流反应的串扰尚不清楚。在此，我们确定BR生物合成基因DWARF（DWF）或关键BR信号基因BRASSINAZOLE-RESISTANT1（BZR1）的过量表达通过正向调节ABA生物合成基因9-CIS-EPOXYCAROTENOID DIOXYGENASE1（NCED1）的表达而增加ABA水平以应对寒害。BR诱导的耐寒性主要依赖于ABA的生物合成。寒冷胁迫或高BR水平降低了BR信号的负调节器BRASSINOSTEROID-INSENSITIVE2（BIN2）的丰度。此外，我们观察到，寒流胁迫增加了BR水平，导致BZR1的积累。BIN2通过抑制ABA的生物合成，对BZR1蛋白的积累和耐寒性都有负向调节。我们的研究结果表明，BR信号通过ABA的生物合成对番茄的耐寒性有积极的调节作用。该研究对园艺中温暖气候作物的生产有意义。

关于BR和ABA文章多，看似不一致的地方也多，也许还有些本质问题没有触及到。