Drought represents a major threat to crop growth and yields. Strigolactones (SLs) contribute to regulating shoot branching by targeting the SUPPRESSOR OF MORE AXILLARY GROWTH2 (MAX2)-LIKE6 (SMXL6), SMXL7 and SMXL8 for degradation in a MAX2-dependent manner in Arabidopsis. Although SLs are implicated in plant drought response, the functions of the SMXL6, 7 and 8 in the SL-regulated plant response to drought stress have remained unclear. Here, we performed transcriptomic, physiological and biochemical analyses of smxl6, 7, 8 and max2 plants to understand the basis for SMXL6/7/8-regulated drought response. We found that three D53 (DWARF53)-Like SMXL members, SMXL6, 7 and 8, are involved in drought response as the smxl6smxl7smxl8 triple mutants showed markedly enhanced drought tolerance compared to wild type (WT). The smxl6smxl7smxl8 plants exhibited decreased leaf stomatal index, cuticular permeability and water loss, and increased anthocyanin biosynthesis during dehydration. Moreover, smxl6smxl7smxl8 were hypersensitive to ABA-induced stomatal closure and ABA responsiveness during and after germination. In addition, RNA-sequencing analysis of the leaves of the D53-like smxl mutants, SL-response max2 mutant and WT plants under normal and dehydration conditions revealed an SMXL6/7/8-mediated network controlling plant adaptation to drought stress via many stress- and/or ABA-responsive and SL-related genes. These data further provide evidence for crosstalk between ABA- and SL-dependent signaling pathways in regulating plant responses to drought. Our results demonstrate that SMXL6, 7 and 8 are vital components of SL signaling and are negatively involved in drought responses, suggesting that genetic manipulation of SMXL6/7/8-dependent SL signaling may provide novel ways to improve drought resistance.

中文翻译：

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MAX2 1（SMAX1）-类似的SMXL6，SMXL7和SMXL8的抑制子在拟南芥中对干旱胁迫起负调节作用。

干旱对作物生长和单产构成重大威胁。硬皮内酯（SLs）通过靶向更多腋窝生长抑制蛋白2（MAX2）-LIKE6（SMXL6），SMXL7和SMXL8抑制拟南芥中MAX2依赖性的方式来调节芽分支。尽管SL与植物的干旱反应有关，但SMXL6、7和8在SL调控植物对干旱胁迫的反应中的功能仍不清楚。在这里，我们进行的转录，生理和生化分析smxl6，7，8和MAX2植物理解为SMXL6 / 7/8-调节干旱响应的基础。我们发现像DXL（DWARF53）这样的三个SM53成员SMXL6、7和8参与了干旱响应，因为与野生型（WT）相比，smxl6smxl7smxl8三重突变体显示出明显增强的耐旱性。所述smxl6smxl7smxl8表现出降低的植物叶气孔指数，表皮渗透性和水的损失，并且在脱水过程中增加花青素的生物合成。此外，smxl6smxl7smxl8对发芽期间和发芽后ABA诱导的气孔关闭和ABA反应高度敏感。此外，D53样smxl突变体叶片的RNA测序分析，SL反应max2在正常和脱水条件下的突变体和野生型植物显示出SMXL6 / 7/8介导的网络通过许多胁迫和/或ABA响应和SL相关基因控制植物对干旱胁迫的适应性。这些数据进一步提供了ABA依赖性和SL依赖性信号传导途径在调节植物对干旱反应中的串扰的证据。我们的结果表明，SMXL6、7和8是SL信号转导的重要组成部分，并且与干旱反应负相关，这表明对SMXL6 / 7/8依赖的SL信号转基因的基因操作可能提供提高抗旱性的新方法。