Abstract
Leaf senescence, which is the last developmental phase of plant growth, is controlled by multiple genetic and environmental factors. Leaf yellowing is a visual indicator of senescence due to the loss of the green pigment chlorophyll. During senescence, the methodical disassembly of macromolecules occurs, facilitating nutrient recycling and translocation from the sink to the source organs, which is critical for plant fitness and productivity. Leaf senescence is a complex and tightly regulated process, with coordinated actions of multiple pathways, responding to a sophisticated integration of leaf age and various environmental signals. Many studies have been carried out to understand the leaf senescence-associated molecular mechanisms including the chlorophyll breakdown, phytohormonal and transcriptional regulation, interaction with environmental signals, and associated metabolic changes. The metabolic reprogramming and nutrient recycling occurring during leaf senescence highlight the fundamental role of this developmental stage for the nutrient economy at the whole plant level. The strong impact of the senescence-associated nutrient remobilization on cereal productivity and grain quality is of interest in many breeding programs. This review summarizes our current knowledge in rice on (i) the actors of chlorophyll degradation, (ii) the identification of stay-green genotypes, (iii) the identification of transcription factors involved in the regulation of leaf senescence, (iv) the roles of leaf-senescence-associated nitrogen enzymes on plant performance, and (v) stress-induced senescence. Compiling the different advances obtained on rice leaf senescence will provide a framework for future rice breeding strategies to improve grain yield.
Highlights
The leaf is the primary photosynthetic organ for energy production and nutrient assimilation at the growth and mature development stages [1]
During the last few years, there have been significant advances in understanding the mechanisms and processes underlying rice leaf senescence. These include the dissection of the Chl degradation pathways, the characterization of stay-green traits, the investigation of the transcriptional regulations and interaction between transcription factors (TFs) and phytohormones, and the dissection of impacts on nutrient remobilization and rice yield production
As in many other monocarpic cereals, grain production is concomitant with plant senescence, and the seed maturation ends with plant death
Summary
The leaf is the primary photosynthetic organ for energy production and nutrient assimilation at the growth and mature development stages [1]. Rice is a monocarpic plant in which leaf senescence overlaps the reproductive stage; premature senescence can reduce grain yield under adverse environmental conditions [6]. In cereal crops such as rice, all the nutrients are transported predominantly from leaves to grains [8]. As genome-wide alterations in gene expression occur during leaf senescence, genes that are controlling leaf senescence in plants are designated as senescence-associated genes (SAGs), and many SAGs have been isolated and characterized in rice [13,14,15,16] They are involved in the degradation of macromolecules, nutrient relocation, defense mechanisms, transcriptional regulation, and signal transduction [1,16]. It includes knowledge about the chlorophyll degradation pathway, description of stay-green traits, transcriptional regulations, impacts of leaf senescence on N metabolism, the relationship between senescence and stress, and it proposes perspectives for the future
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