The ratio of red light to far‐red light (R:FR) is perceived by phytochrome B (phyB) and informs plants of nearby competition. A low R:FR indicative of competition induces the shade avoidance syndrome and suppresses branching by incompletely understood mechanisms. Phytochrome interacting factors (PIFs) are transcription factors targeted by phytochromes to evoke photomorphogenic responses. PIF4 and PIF5 promote shade avoidance responses and become inactivated by direct interaction with active phyB in the nucleus. Here, genetic and physiological assays show that PIF4 and PIF5 contribute to the suppression of branching resulting from phyB loss of function and a low R:FR, although roles for other PIFs or pathways may exist. The suppression of branching is associated with PIF4/PIF5 promotion of the expression of the branching inhibitor BRANCHED 1 and abscisic acid (ABA) accumulation in axillary buds and is dependent on the function of the key ABA biosynthetic enzyme Nine‐cis‐epoxycarotenoid dioxygenase 3. However, PIF4/PIF5 function is not confined to a single hormonal pathway, as they also promote stem indole‐3‐acetic acid accumulation and stimulate systemic auxin signalling, which contribute to the suppression of bud growth when phyB is inactive.

中文翻译：

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植物色素相互作用因子4和5通过芽脱落酸和茎生长素信号传导调节腋窝分支。

植物色素B（phyB）感知红光与远红光的比率（R：FR），并通知植物附近的竞争。指示竞争的低R：FR引起避光综合症，并通过不完全了解的机制抑制分支。植物色素相互作用因子（PIF）是植物色素靶向的转录因子，可引起光形态发生反应。PIF4和PIF5促进避光反应，并通过与细胞核中的phyB直接相互作用而失活。在这里，遗传和生理学检测表明，PIF4和PIF5有助于抑制phyB功能丧失和低R：FR导致的分支，尽管可能存在其他PIF或途径的作用。抑制分支与PIF4 / PIF5促进分支抑制剂表达有关分支1和脱落酸（ABA）在腋芽中的积累，并依赖于关键ABA生物合成酶Nine-顺式-环氧类胡萝卜素双加氧酶3的功能。但是，PIF4 / PIF5的功能并不局限于单一的激素途径，因为它们也促进茎吲哚-3-乙酸积累并刺激系统性生长素信号传导，当phyB不活跃时，这有助于抑制芽的生长。