Characterization of a New Gene Controlling Leaf Senescence using Progeny from an Interspecific Cross in Rice

Full text: An analysis of quantitative trait loci (QTL) controlling chlorophyll content was conducted using introgression lines (CR7501 and CR2002) derived from a cross between the Oryza sativa japonica cultivar 'Hwaseong' as a recurrent parent and wild species O. grandiglumis as a donor parent. These two lines showed higher chlorophyll content than Hwaseong. For QTL analysis, we constructed 58 F3 and 17 F4 lines from the cross CR7501/Hwaseong. SSR markers were used for genotyping the lines. One-way ANOVA indicated the presence of a QTL for chlorophyll content (qCC2) on chromosome 2 and qCC2 explained 24.6% of the phenotypic variance. To examine whether qCC2 is also involved in senescence, a series of dark-induced senescence (DIS) experiments were conducted. Detached leaves from Hwaseong and CR2002 were incubated in 3mM MES buffer (pH 5.8) at 27℃ under complete dark condition. CR2002 showed higher chlorophyll content with delayed senescence than Hwaseong. To know whether qCC2 maintains leaf functionality during DIS, ion leakage test and Fv/Fm measurement were performed. The Fv/Fm value displayed significant difference between CR2002 and Hwseong at 6 days after incubation, while ion leakage rate was not significantly different. These results might imply that qCC2 is associated with chlorophyll content and stay-green phenotype. The qCC2 QTL region harbours GW2 locus encoding the RING-type E3 ubiquitin ligase controlling grain size. To know the possible relationship between the GW2 activity and senescence, gw2-knockout mutant (gw2-ko) and the wild type plants were incubated under dark condition. gw2-ko showed delayed senescence in DIS, suggesting that GW2 is possibly related to stay-green phenotype. (author)