A STAY‐GREEN protein SlSGR1 regulates lycopene and β‐carotene accumulation by interacting directly with SlPSY1 during ripening processes in tomato

Abstract

SummaryAs a primary source of lycopene in the human diet, fleshy fruits synthesize this compound both de novo and via chlorophyll metabolism during ripening. SlSGR1 encodes a STAY-GREEN protein that plays a critical role in the regulation of chlorophyll degradation in tomato leaves and fruits.We report that SlSGR1 can regulate tomato (Solanum lycopersicum) lycopene accumulation through direct interaction with a key carotenoid synthetic enzyme SlPSY1, and can inhibit its activity. This interaction with SlSGR1 mediates lycopene accumulation during tomato fruit maturation. We confirmed this inhibitory activity in bacteria engineered to produce lycopene, where the introduction of SlSGR1 reduced dramatically lycopene biosynthesis.The repression of SlSGR1 in transgenic tomato fruits resulted in altered accumulation patterns of phytoene and lycopene, whilst simultaneously elevating SlPSY1 mRNA accumulation and plastid conversion at the early stages of fruit ripening, resulting in increased lycopene and b-carotene (four-and nine-fold, respectively) in red ripe fruits.SlSGR1 influences ethylene signal transduction via the altered expression of ethylene receptor genes and ethylene-induced genes. Fruit shelf-life is extended significantly in SlSGR1-repressed tomatoes. Our results indicate that SlSGR1 plays a pivotal regulatory role in color formation and fruit ripening regulation in tomato, and further suggest that SlSGR1 activity is mediated through direct interaction with PSY1.

Different Mechanisms Are Responsible for Chlorophyll Dephytylation during Fruit Ripening and Leaf Senescence in Tomato

“…As a consequence, mutants that are deficient in SGR exhibit a stay-green phenotype (Barry, 2009;Hörtensteiner, 2009). In addition, SGR (negatively) regulates carotenoid biosynthesis during tomato fruit ripening (Luo et al, 2013) and (positively) regulates root nodule senescence in Medicago truncatula (Zhou et al, 2011), implying that SGR has diverse functions that are not restricted to chlorophyll degradation.…”

Molecular cloning and characterization of a chlorophyll degradation regulatory gene (ZjSGR) from Zoysia japonica

“…The identification of stay-green mutants in several plant species has made it possible to further investigate the underlying mechanism (Armstead et al, 2006;Park et al, 2007;Zhou et al, 2011). Stay-green (SGR) proteins play important roles in the regulation of plant chlorophyll degradation and senescence, and they have been characterized in Arabidopsis thaliana (Ren et al, 2007), Medicago truncatula (Zhou et al, 2011), and Solanum lycopersicum (Luo et al, 2013). Constitutively increased SGR levels resulted in accelerated chlorophyll degradation in Arabidopsis leaves (Ren et al, 2007).…”

Genome-wide identification and analysis of the SGR gene family in Cucumis melo L.

“…The breakdown of CHL is catalyzed by several CHL catabolic enzymes in an enzymatic process (Rong et al, 2013). Several genes (SGR,RCCR,PAO,PPH,NYC1,and NOL) regulating the process of leaf senescence and fruit ripening have been identified (Lim et al, 2003;Hörtensteiner and Kräutler, 2011;Luo et al, 2013). Senescence-associated gene (SGR) plays a critical role in the regulation of CHL degradation and senescence.…”

“…Chloroplast-located proteins encoded by SGR genes in different species are well conserved in higher plants, and it is expected that SGR interacts with subunits of the light harvesting complex of PSII (Park et al, 2007;Hörtensteiner, 2009). In recent years, the functions of the products of SGR genes have been identified in Arabidopsis thaliana (Sakuraba et al, 2012), Oryza sativa (Jiang et al, 2007), Pisum sativum (Sato et al, 2007), Solanum lycopersicum (Akhtar et al, 1999;Luo et al, 2013), Triticum aestivum (Spano et al, 2003), and other species. Expression of SGR in Arabidopsis and tobacco induces the degradation and senescence of leaf CHL (Park et al, 2007;Ren et al, 2007;Grassl et al, 2012).…”

“…Expression of SGR in Arabidopsis and tobacco induces the degradation and senescence of leaf CHL (Park et al, 2007;Ren et al, 2007;Grassl et al, 2012). Silencing of SGR by RNA interference (RNAi) leads to reduced CHL degradation in leaves and fruits Zhou et al, 2011;Luo et al, 2013).…”