Abstract
Leaf senescence, being the final developmental stage of the leaf, signifies the transition from a mature, photosynthetically active organ to the attenuation of said function and eventual death of the leaf. During senescence, essential nutrients sequestered in the leaf, such as phosphorus (P), are mobilized and transported to sink tissues, particularly expanding leaves and developing seeds. Phosphorus recycling is crucial, as it helps to ensure that previously acquired P is not lost to the environment, particularly under the naturally occurring condition where most unfertilized soils contain low levels of soluble orthophosphate (Pi), the only form of P that roots can directly assimilate from the soil. Piecing together the molecular mechanisms that underpin the highly variable efficiencies of P remobilization from senescing leaves by different plant species may be critical for devising effective strategies for improving overall crop P-use efficiency. Maximizing Pi remobilization from senescing leaves using selective breeding and/or biotechnological strategies will help to generate P-efficient crops that would minimize the use of unsustainable and polluting Pi-containing fertilizers in agriculture. This review focuses on the molecular mechanisms whereby P is remobilized from senescing leaves and transported to sink tissues, which encompasses the action of hormones, transcription factors, Pi-scavenging enzymes, and Pi transporters.
Highlights
Phosphorus (P) is a crucial plant macronutrient, as it is a structural constituent of essential biomolecules involved in both energy metabolism, such as ATP and PPi, and in the formation of key macromolecules such as nucleic acids and phospholipids
Leaf senescence is a critical component of the life cycle for a plant as it allows for the investment of resources into new tissues
The Pi remobilization process requires the coordinated function of hormones and transcription factors to initiate signaling cascades, resulting in the action of hydrolases that can liberate Pi from P-containing molecules including nucleic acids, phospholipids, phosphoanhydrides, and Pi-ester-containing metabolites
Summary
Phosphorus (P) is a crucial plant macronutrient, as it is a structural constituent of essential biomolecules involved in both energy metabolism, such as ATP and PPi, and in the formation of key macromolecules such as nucleic acids and phospholipids. It becomes clear that an alternative and sustainable approach is required to reduce agriculture’s dependence on Pi fertilizers This may be achieved through the manipulation of the crops themselves by either improving the: (i) ability of their roots to assimilate Pi from the soil, relating to P-acquisition efficiency, and/or (ii) proficiency of Pi recycling within the plant itself, known as P-use efficiency (PUE) [4]. An integrated understanding of Pi remobilization during senescence will facilitate development of effective biotechnological strategies to improve crop PUE, thereby reducing society’s dependency upon polluting and unsustainable Pi-containing fertilizers. Several studies have investigated gene expression changes during leaf senescence by analyzing genome-wide transcriptomes of leaves undergoing this final phase of development These studies have provided a wealth of knowledge through large-scale comparisons of genes and gene families that are up-regulated or down-regulated during the senescence syndrome. The transcriptomic response of regulatory elements known to influence downstream targets that function in Pi remobilization during leaf senescence are explored
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