Strigolactones are a group of phytohormones that control developmental processes including shoot branching and various plant–environment interactions in plants. We previously showed that the strigolactone perception mutant more axillary branches 2 (max2) has increased susceptibility to plant pathogenic bacteria. Here we show that both strigolactone biosynthesis (max3 and max4) and perception mutants (max2 and dwarf14) are significantly more sensitive to Pseudomonas syringae DC3000. Moreover, in response to P. syringae infection, high levels of SA accumulated in max2 and this mutant was ozone sensitive. Further analysis of gene expression revealed no major role for strigolactone in regulation of defense gene expression. In contrast, guard cell function was clearly impaired in max2 and depending on the assay used, also in max3, max4, and d14 mutants. We analyzed stomatal responses to stimuli that cause stomatal closure. While the response to abscisic acid (ABA) was not impaired in any of the mutants, the response to darkness and high CO₂ was impaired in max2 and d14‐1 mutants, and to CO₂ also in strigolactone synthesis (max3, max4) mutants. To position the role of MAX2 in the guard cell signaling network, max2 was crossed with mutants defective in ABA biosynthesis or signaling. This revealed that MAX2 acts in a signaling pathway that functions in parallel to the guard cell ABA signaling pathway. We propose that the impaired defense responses of max2 are related to higher stomatal conductance that allows increased entry of bacteria or air pollutants like ozone. Furthermore, as MAX2 appears to act in a specific branch of guard cell signaling (related to CO₂ signaling), this protein could be one of the components that allow guard cells to distinguish between different environmental conditions.

中文翻译：

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MAX2和松果内酯在病原体，臭氧和气孔响应中的差异作用。

内酯角内酯是一组植物激素，它们控制发育过程，包括枝条分支和植物中各种植物与环境的相互作用。我们先前显示，strigolactone感知突变体更多的腋生分支2（max2）已增加对植物病原细菌的敏感性。在这里，我们显示了strigolactone生物合成（max3和max4）和感知突变体（max2和dwarf14）对丁香假单胞菌DC3000的敏感性更高。此外，针对丁香假单胞菌感染，max2中积累了高水平的SA这个突变体对臭氧很敏感 基因表达的进一步分析显示，Strigolactone在防御基因表达的调节中没有主要作用。相反，在max2中以及根据所使用的测定法，在max3，max4和d14突变体中，保卫细胞功能也明显受损。我们分析了气孔对引起气孔关闭的刺激的反应。虽然在任何一个突变体中对脱落酸（ABA）的响应均不受影响，但在max2和d14-1突变体中对黑暗和高CO ₂的响应均受到损害，而在strigolactone合成中对CO ₂的响应也有所减弱（max3，max4）的突变体。为了定位MAX2在保卫细胞信号传导网络中的作用，将max2与ABA生物合成或信号传导缺陷的突变体杂交。这揭示了MAX2在与保卫细胞ABA信号传导途径平行起作用的信号传导途径中起作用。我们认为max2的防御反应受损与较高的气孔导度有关，气孔导度允许细菌或空气污染物（如臭氧）的进入增加。此外，由于MAX2似乎在保卫细胞信号传导的特定分支中起作用（与CO ₂信号传导有关），因此该蛋白质可能是允许保卫细胞区分不同环境条件的成分之一。