Xiong Yali, Song Xiaoyun, Mehra Poonam, Yu Suhang, Li Qiaoyi, Tashenmaimaiti Dilixiadanmu, Bennett Malcolm, Kong Xiuzhen, Bhosale Rahul, Huang Guoqiang
Joint International Research Laboratory of Metabolic & Developmental Sciences, State Key Laboratory of Hybrid Rice, SJTU-University of Adelaide Joint Centre for Agriculture and Health, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China.
School of Biosciences, University of Nottingham, Nottingham LE12 5RD, UK.
Curr Biol. 2025 Feb 3;35(3):542-553.e4. doi: 10.1016/j.cub.2024.12.003. Epub 2025 Jan 10.
Enhancing drought resistance through the manipulation of root system architecture (RSA) in crops represents a crucial strategy for addressing food insecurity challenges. Abscisic acid (ABA) plays important roles in drought tolerance; yet, its molecular mechanisms in regulating RSA, especially in cereal crops, remain unclear. In this study, we report a new mechanism whereby ABA mediates local auxin biosynthesis to regulate root gravitropic response, thereby controlling the alteration of RSA in response to drought in cereal crops. Under drought conditions, wild-type (WT) plants displayed a steep root angle compared with normal conditions, while ABA biosynthetic mutants (mhz4, mhz5, osaba1, and osaba2) showed a significantly shallower crown root angle. Gravitropic assays revealed that ABA biosynthetic mutants have reduced gravitropic responses compared with WT plants. Hormone profiling analysis indicated that the mhz5 mutant has reduced auxin levels in root tips, and exogenous auxin (naphthaleneacetic acid [NAA]) application restored its root gravitropic defects. Consistently, auxin reporter analysis in mhz5 showed a reduced auxin gradient formation in root epidermis during gravitropic bending response compared with WT plants. Furthermore, NAA, rather than ABA, was able to rescue the compromised gravitropic response in the auxin biosynthetic mutant mhz10-1/tryptophan amino transferase2 (ostar2). Additionally, the maize ABA biosynthetic mutant viviparous5 (vp5) also showed gravitropic defects and a shallower seminal root angle than WT plants, which were restored by external auxin treatment. Collectively, we suggest that ABA-induced auxin synthesis governs the root gravitropic machinery, thereby influencing root angle in rice, maize, and possibly other cereal crops.
通过调控作物根系结构（RSA）来增强抗旱性是应对粮食安全挑战的关键策略。脱落酸（ABA）在耐旱性中发挥重要作用；然而，其调控RSA的分子机制，尤其是在谷类作物中，仍不清楚。在本研究中，我们报道了一种新机制，即ABA介导局部生长素生物合成以调节根的向重力性反应，从而控制谷类作物根系结构在干旱响应中的改变。在干旱条件下，野生型（WT）植株与正常条件相比根角度变陡，而ABA生物合成突变体（mhz4、mhz5、osaba1和osaba2）的冠根角度明显变浅。向重力性测定表明，与WT植株相比，ABA生物合成突变体的向重力性反应减弱。激素谱分析表明，mhz5突变体根尖的生长素水平降低，外源生长素（萘乙酸 [NAA]）处理恢复了其根的向重力性缺陷。一致地，与WT植株相比，mhz5中生长素报告基因分析显示在向重力性弯曲反应期间根表皮中生长素梯度形成减少。此外，NAA而非ABA能够挽救生长素生物合成突变体mhz10-1/色氨酸氨基转移酶2（ostar2）受损的向重力性反应。此外，玉米ABA生物合成突变体胎萌5（vp5）也表现出向重力性缺陷，且胚根角度比WT植株更浅，外源生长素处理可恢复此缺陷。总体而言，我们认为ABA诱导的生长素合成控制根的向重力性机制，从而影响水稻、玉米以及可能其他谷类作物的根角度。
