Abstract
Leaf senescence is an integrated response of the cells to develop age information and various environmental signals. Thus, some of the genes involved in the response to environmental changes are expected to regulate leaf senescence. Light acts not only as the primary source of energy for photosynthesis but also as an essential environmental cue that directly control plant growth and development including leaf senescence. The molecular mechanisms linking light signaling to leaf senescence have recently emerged, exploring the role of Phytochrome-Interacting Factors (PIFs) as a central player leading to diverse senescence responses, senescence-promoting gene regulatory networks (GRNs) involving PIFs, and structural features of transcription modules in GRNs. The circadian clock is an endogenous time-keeping system for the adaptation of organisms to changing environmental signals and coordinates developmental events throughout the life of the plant. Circadian rhythms can be reset by environmental signals, such as light-dark or temperature cycles, to match the environmental cycle. Research advances have led to the discovery of the role of core clock components as senescence regulators and their underlying signaling pathways, as well as the age-dependent shortening of the circadian clock period. These discoveries highlight the close relationship between the circadian system and leaf senescence. Key issues remain to be elucidated, including the effect of light on leaf senescence in relation to the circadian clock, and the identification of key molecules linking aging, light, and the circadian clock, and integration mechanisms of various senescence-affecting signals at the multi-regulation levels in dynamics point of view.
Highlights
Leaves are crucial to plant growth and survival
In addition to alterations of signal transduction, pif4 mutants show attenuated induction of ethylene biosynthesis by darkness (Song et al, 2014). These results suggest that Phytochrome-Interacting Factors (PIFs) play an important role in transducing light information to abscisic acid (ABA) and ethylene pathways, thereby activating leaf senescence responses (Figure 1A)
PIF4 acts as a repressor of GLKs (Song et al, 2014). These findings suggest that the intricate gene regulatory networks (GRNs) governed by PIF4, PIF5, EIN3, EM LEVEL (EEL), ABI5, and ORE1 are linked, thereby forming multiple coherent feedforward loops
Summary
Leaves are crucial to plant growth and survival. During early development, emerged leaves become photosynthetic organs that convert light energy into nutrients that are necessary for plant growth. Cellular constituents generated during the growth phase of leaves are converted into mobilizable nutrients and relocated to other developing organs. Leaf senescence is an integral part of development despite the associated degenerative physiological changes. Under favorable conditions, this process occurs at age-dependent manner by an innate developmental program. This process occurs at age-dependent manner by an innate developmental program Unfavorable conditions, such as darkness or abiotic and biotic stresses, can induce premature leaf senescence, which shortens the lifespan of individual leaves. We review recent findings on leaf senescence, the role of light and circadian clock, and how the senescenceregulatory networks are interacting with these signals. We discuss the temporal and light-mediated regulation of plant physiology in relation to leaf senescence, which will contribute to understand the fitness and adaptive advantage of higher plants
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