Plant leaf senescence and death – regulation by multiple layers of control and implications for aging in general

Abstract

SummaryHow do organisms, organs, tissues and cells change their fate when they age towards senescence and death? Plant leaves provide a unique window to explore this question because they show reproducible life history and are readily accessible for experimental assays. Throughout their lifespan, leaves undergo a series of developmental, physiological and metabolic transitions that culminate in senescence and death. Leaf senescence is an 'altruistic death' that allows for the degradation of the nutrients that are produced during the growth phase of the leaf and their redistribution to developing seeds or other parts of the plant, and thus is a strategy that has evolved to maximize the fitness of the plant. During the past decade, there has been significant progress towards understanding the key molecular principles of leaf senescence using genetic and molecular studies, as well as 'omics' analyses. It is now apparent that leaf senescence is a highly complex genetic program that is tightly controlled by multiple layers of regulation, including at the level of chromatin and transcription, as well as by post-transcriptional, translational and post-translational regulation. This Commentary discusses the latest understandings and insights into the underlying molecular mechanisms, and presents the perspectives necessary to enable our systemlevel understanding of leaf senescence, together with their possible implications for aging in general.

Transcription Factor ATAF1 in Arabidopsis Promotes Senescence by Direct Regulation of Key Chloroplast Maintenance and Senescence Transcriptional Cascades

“…Indeed, as we show here, ABA-/H 2 O 2 -dependent expression changes are impaired in ataf1 mutants but stimulated in ATAF1 overexpressors (Supplemental Table S6). Thus, our data extend the existing molecular model of ORE1 regulation (Kim et al, 2009;Woo et al, 2013) by adding a further layer of control connecting it, via ATAF1, to ABA-and H 2 O 2 -dependent stress signaling (Fig. 9).…”

GROWTH REGULATING FACTOR5 Stimulates Arabidopsis Chloroplast Division, Photosynthesis, and Leaf Longevity

“…The higher Chl levels and increased photosynthetic CO 2 uptake in 1-month-old 35S:GRF5 leaves could directly lead to a delay in leaf senescence, since senescence is only initiated when the photosynthetic rate drops below a certain threshold, which is accompanied by chloroplast and Chl breakdown (Lim et al, 2007). Simultaneously, leaf senescence is tightly regulated by genetic programs (Woo et al, 2013) in which GRF5 could actively function beyond the leaf cell division phase. This is supported by the observation that the stimulating effects of a miR396-insensitive version of GRF3 (rGRF3) on cell division and leaf longevity could be uncoupled (Debernardi et al, 2014).…”

A Rice NAC Transcription Factor Promotes Leaf Senescence via ABA Biosynthesis

“…For example, macromolecules including lipids, proteins, and nucleic acids are hydrolyzed, which leads to disassembly of mitochondria and nuclei, and to cell death (Buchanan-Wollaston et al, 2005;Ulker et al, 2007). Although senescence is an active process to salvage nutrients from old tissues, precocious senescence will shorten the growth stage of crops and be unfavorable to agronomic production (Woo et al, 2013).The most distinguishing feature in leaf senescence is the yellowing phenotype, which is a visible marker of the degradation of macromolecules (Kim et al, 2006). The chlorophyll degradation pathway is one of the most characterized ones for macromolecule degradation in plants (Hörtensteiner, 2006).…”

“…For example, macromolecules including lipids, proteins, and nucleic acids are hydrolyzed, which leads to disassembly of mitochondria and nuclei, and to cell death (Buchanan-Wollaston et al, 2005;Ulker et al, 2007). Although senescence is an active process to salvage nutrients from old tissues, precocious senescence will shorten the growth stage of crops and be unfavorable to agronomic production (Woo et al, 2013).…”