ARC Centre of Excellence in Plant Energy Biology, School of Molecular Sciences, University of Western Australia, Perth, Western Australia 6009, Australia.
Department of Biology, Lund University, Lund 22362, Sweden.
Plant Physiol. 2021 Aug 3;186(4):2205-2221. doi: 10.1093/plphys/kiab195.
Recent studies in Arabidopsis (Arabidopsis thaliana) have reported conflicting roles for NAC DOMAIN CONTAINING PROTEIN 17 (ANAC017), a transcription factor regulating mitochondria-to-nuclear signaling, and its closest paralog NAC DOMAIN CONTAINING PROTEIN 16 (ANAC016), in leaf senescence. By synchronizing senescence in individually darkened leaves of knockout and overexpressing mutants from these contrasting studies, we demonstrate that elevated ANAC017 expression consistently causes accelerated senescence and cell death. A time-resolved transcriptome analysis revealed that senescence-associated pathways such as autophagy are not constitutively activated in ANAC017 overexpression lines, but require a senescence-stimulus to trigger accelerated induction. ANAC017 transcript and ANAC017-target genes are constitutively upregulated in ANAC017 overexpression lines, but surprisingly show a transient "super-induction" 1 d after senescence induction. This induction of ANAC017 and its target genes is observed during the later stages of age-related and dark-induced senescence, indicating the ANAC017 pathway is also activated in natural senescence. In contrast, knockout mutants of ANAC017 showed lowered senescence-induced induction of ANAC017 target genes during the late stages of dark-induced senescence. Finally, promoter binding analyses show that the ANAC016 promoter sequence is directly bound by ANAC017, so ANAC016 likely acts downstream of ANAC017 and is directly transcriptionally controlled by ANAC017 in a feed-forward loop during late senescence.
最近在拟南芥（Arabidopsis thaliana）中的研究报告称，调节线粒体到核信号的转录因子 NAC 结构域包含蛋白 17（ANAC017）及其最近的同源物 NAC 结构域包含蛋白 16（ANAC016）在叶片衰老中发挥了相互矛盾的作用。通过在这些对比研究的敲除和过表达突变体的单独变暗叶片中同步衰老，我们证明了升高的 ANAC017 表达一致导致加速衰老和细胞死亡。时间分辨的转录组分析表明，衰老相关途径如自噬在 ANAC017 过表达系中没有被组成性激活，而是需要衰老刺激来触发加速诱导。ANAC017 转录本和 ANAC017 靶基因在 ANAC017 过表达系中持续上调，但令人惊讶的是，在衰老诱导后 1 天表现出短暂的“超诱导”。在年龄相关和黑暗诱导的衰老后期观察到 ANAC017 和其靶基因的这种诱导，表明 ANAC017 途径也在自然衰老中被激活。相比之下，ANAC017 的敲除突变体在黑暗诱导的衰老后期显示出降低的衰老诱导的 ANAC017 靶基因的诱导。最后，启动子结合分析表明，ANAC016 启动子序列直接被 ANAC017 结合，因此 ANAC016 可能在 ANAC017 下游起作用，并且在晚期衰老期间通过前馈环直接受 ANAC017 的转录控制。
