Rai Snigdha, Lemke Matthew D, Arias Anika M, Gomez Mendez Maria F, Dehesh Katayoon, Woodson Jesse D
The School of Plant Sciences, University of Arizona, Tucson, AZ.
Department of Botany and Plant Sciences, Institute for Integrative Genome Biology, University of California, Riverside, CA.
bioRxiv. 2024 Nov 26:2024.05.13.593788. doi: 10.1101/2024.05.13.593788.
In response to environmental stresses, chloroplasts generate reactive oxygen species, including singlet oxygen (O), an excited state of oxygen that regulates chloroplast-to-nucleus (retrograde) signaling, chloroplast turnover, and programmed cell death (PCD). Yet, the central signaling mechanisms and downstream responses remain poorly understood. The () mutant conditionally accumulates O and Plant U-Box 4 (PUB4), a cytoplasmic E3 ubiquitin ligase, is involved in propagating O signals for chloroplast turnover and cellular degradation. Thus, the and mutants are useful genetic tools to elucidate these signaling pathways. Previous studies have focused on the role of O in promoting cellular degradation in mutants, but its impact on retrograde signaling from mature chloroplasts (the major site of O production) is poorly understood.
To gain mechanistic insights into O signaling pathways, we compared transcriptomes of adult wt, , and plants. The accumulation of O in plants broadly repressed genes involved in chloroplast function and photosynthesis, while inducing genes and transcription factors involved in abiotic and biotic stress, the biosynthesis of jasmonic acid (JA) and salicylic acid (SA), microautophagy, and senescence. Elevated JA and SA levels were observed in O-stressed plants. reversed most of this O-induced gene expression and reduced the JA content in plants. The mutation also blocked JA-induced senescence pathways in the dark. However maintained constitutively elevated levels of SA even in the absence of bulk O accumulation.
Together, this work demonstrates that in plants, O leads to a robust retrograde signal that may protect cells by downregulating photosynthesis and ROS production while simultaneously mounting a stress response involving SA and JA. The induction of microautophagy and senescence pathways indicate that O-induced cellular degradation is a genetic response to this stress, and the bulk of this transcriptional response is modulated by the PUB4 protein. However, the effect of on hormone synthesis and signaling is complex and indicates that an intricate interplay of SA and JA are involved in promoting stress responses and programmed cell death during photo-oxidative damage.
为响应环境胁迫，叶绿体产生活性氧，包括单线态氧（O），一种氧的激发态，其调节叶绿体到细胞核（逆行）信号传导、叶绿体周转和程序性细胞死亡（PCD）。然而，核心信号传导机制和下游反应仍知之甚少。（）突变体有条件地积累O，并且植物泛素盒4（PUB4），一种细胞质E3泛素连接酶，参与传播O信号以促进叶绿体周转和细胞降解。因此，和突变体是阐明这些信号通路的有用遗传工具。先前的研究集中于O在促进突变体细胞降解中的作用，但其对来自成熟叶绿体（O产生的主要部位）的逆行信号传导的影响了解甚少。
为深入了解O信号通路的机制，我们比较了成年野生型、和植物的转录组。植物中O的积累广泛抑制了参与叶绿体功能和光合作用的基因，同时诱导了参与非生物和生物胁迫、茉莉酸（JA）和水杨酸（SA）生物合成、微自噬和衰老的基因及转录因子。在O胁迫的植物中观察到JA和SA水平升高。逆转了大部分这种由O诱导的基因表达，并降低了植物中的JA含量。突变还阻断了黑暗中JA诱导的衰老途径。然而，即使在没有大量O积累的情况下，仍维持SA的组成性高水平。
总之，这项工作表明，在植物中，O导致强大的逆行信号，该信号可能通过下调光合作用和ROS产生来保护细胞，同时引发涉及SA和JA的应激反应。微自噬和衰老途径的诱导表明，O诱导的细胞降解是对这种胁迫的遗传反应，并且这种转录反应的大部分由PUB4蛋白调节。然而，对激素合成和信号传导的影响是复杂的，表明SA和JA的复杂相互作用参与了光氧化损伤期间促进应激反应和程序性细胞死亡。
