Abstract
Leaf senescence is the final stage of plant development. Many internal and external factors affect the senescence process in rice (Oryza sativa L.). In this study, we identified qCC2, a major quantitative trait locus (QTL) for chlorophyll content using a population derived from an interspecific cross between O. sativa (cv. Hwaseong) and Oryza grandiglumis. The O. grandiglumis allele at qCC2 increased chlorophyll content and delayed senescence. GW2 encoding E3 ubiquitin ligase in the qCC2 region was selected as a candidate for qCC2. To determine if GW2 is allelic to qCC2, a gw2-knockout mutant (gw2-ko) was examined using a dark-induced senescence assay. gw2-ko showed delayed leaf senescence in the dark with down-regulated expression of senescence-associated genes (SAGs) and chlorophyll degradation genes (CDGs). The association of the GW2 genotype with the delayed senescence phenotype was confirmed in an F2 population. RNA-seq analysis was conducted to investigate 30-day-old leaf transcriptome dynamics in Hwaseong and a backcross inbred line—CR2002—under dark treatment. This resulted in the identification of genes involved in phytohormone signaling and associated with senescence. These results suggested that transcriptional regulation was associated with delayed senescence in CR2002, and RING-type E3 ubiquitin ligase GW2 was a positive regulator of leaf senescence in rice.
Highlights
Chlorophyll (Chl) is a photosynthetic pigment that is an essential component of the plant photosystem
To identify loci associated with chlorophyll content and the stay-green phenotype, quantitative trait locus (QTL) analysis was conducted using F3 and F4 populations derived from a cross between Hwaseong and CR2002
A QTL for chlorophyll content was located on chromosome 2 between RM12813 and RM12983. This QTL was repeatedly detected in F3 and F4 generations at both stages, heading (Chlorophyll I) and one month after heading (Chlorophyll II). qCC2 explained 24.6% of the phenotypic variation, and the O. grandiglumis allele contributed to the increased chlorophyll content, indicating that qCC2 was a major QTL responsible for leaf greenness at heading and ripening stage
Summary
Chlorophyll (Chl) is a photosynthetic pigment that is an essential component of the plant photosystem. SGR, a highly conserved senescence-associated gene, encodes a novel chloroplast protein, and the expression of SGR is up-regulated in both natural and dark-induced senescence. This gene interacts with the light-harvesting chlorophyll-binding protein (LHCP) [10,14]. OsNAP contains a typical NAC structure at the N terminus [13] This gene plays a role in regulating leaf senescence and acts as a key component, linking ABA signaling in rice. These genes have been used as ideal markers for the onset of the senescence process
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