Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403, USA.
Plant Cell. 2022 Nov 29;34(12):4897-4919. doi: 10.1093/plcell/koac276.
Signals emanating from chloroplasts influence nuclear gene expression, but roles of retrograde signals during chloroplast development are unclear. To address this gap, we analyzed transcriptomes of non-photosynthetic maize mutants and compared them to transcriptomes of stages of normal leaf development. The transcriptomes of two albino mutants lacking plastid ribosomes resembled transcriptomes at very early stages of normal leaf development, whereas the transcriptomes of two chlorotic mutants with thylakoid targeting or plastid transcription defects resembled those at a slightly later stage. We identified ∼2,700 differentially expressed genes, which fall into six major categories based on the polarity and mutant-specificity of the change. Downregulated genes were generally expressed late in normal development and were enriched in photosynthesis genes, whereas upregulated genes act early and were enriched for functions in chloroplast biogenesis and cytosolic translation. We showed further that target-of-rapamycin (TOR) signaling was elevated in mutants lacking plastid ribosomes and declined in concert with plastid ribosome buildup during normal leaf development. Our results implicate three plastid signals as coordinators of photosynthetic differentiation. One signal requires plastid ribosomes and activates photosynthesis genes. A second signal reflects attainment of chloroplast maturity and represses chloroplast biogenesis genes. A third signal, the consumption of nutrients by developing chloroplasts, represses TOR, promoting termination of cell proliferation during leaf development.
叶绿体发出的信号影响核基因表达，但在叶绿体发育过程中逆行信号的作用尚不清楚。为了解决这一差距，我们分析了非光合作用玉米突变体的转录组，并将其与正常叶片发育阶段的转录组进行了比较。缺乏质体核糖体的两个白化突变体的转录组与正常叶片发育的早期阶段的转录组相似，而具有类囊体靶向或质体转录缺陷的两个黄化突变体的转录组与稍晚的阶段相似。我们鉴定了约 2700 个差异表达基因，这些基因根据极性和突变体特异性分为六大类。下调基因通常在正常发育后期表达，并富含光合作用基因，而上调基因则在早期起作用，并富含叶绿体生物发生和细胞质翻译的功能。我们进一步表明，缺乏质体核糖体的突变体中雷帕霉素（TOR）信号升高，并且在正常叶片发育过程中与质体核糖体的积累协同下降。我们的结果表明，三种质体信号作为光合作用分化的协调者。一种信号需要质体核糖体并激活光合作用基因。第二种信号反映了叶绿体成熟度的获得，并抑制了叶绿体生物发生基因。第三种信号是发育中的叶绿体消耗营养物质，抑制 TOR，促进叶片发育过程中细胞增殖的终止。
