Genetic Characterization And Expression Of Chioroplast Genes Of Chlorophyll-deifcient Mutants In Wheat

Three types of chlorophyll-deficient wheat mutants, i.e., Mt6172, Mt135and Mt18derived fromspaceflight mutagenesis and their wild-type counterparts H6172,60315and XM18respectively wereused to verify the genetic control of chlorophyll-deficient traits and comparatively analyze thephotosynthetic pigments. Chloroplast gene expression pattern in Mt135were also traced by usingRT-PCR analysis. The main results were as follow:1. All of the F1hybrids which derived from Mt6172striped plants crossed with normal plants weregreen. Whereas trait segregation occured in F2generations. The result suggested that chlorophyll-deficient trait of Mt6172were recessively nuclear gene(s) controlled. When the female was Mt135striped plants，offsprings showed character segregation (green, albino, and stripe). While F1generationwere green when the female was normal plants.It indicated that its chlorophyll-deficient trait wascontrolled by nucleo-cytoplasmic interaction. The F1generation of Mt18crossed with normal plantsalso showed inconsistent results. The leaf color of the progenies were same as female parent, indicatingthat the albino trait of Mt18was controlled by cytoplasmic genes.2. The photosynthetic pigments content of the three types mutants and wild-type plants weremeasured at the seedling, reviving, and filling stage, respectively. Compared to wild-type plants,chlorophyll a, b, total chlorophyll, and carotenoid tested in Mt6172abino plants were significantlydecreased which led to the reduction of total chlorophyll. Total photosynthetic pigments of Mt6172striped plants decreased in the seedling and reviving stages as well as in the filling stage whenchlorophyll a/b level increased significantly. Chlorophyll a, b, total chlorophyll, and carotenoid tested inMt135albino plants were decreased too. Photosynthetic pigments in Mt135striped plants weresignificantly decreased during the seedling and reviving stages, but the ratio of chlorophyll a/b wasincreased significantly in the filling stage. Level of all photosynthetic pigments tested in Mt18did notshow significant differences during seedling and filling stage, but decreased significantly at revivingstage. The ratio of chlorophyll a/b in Mt18also decreased at reviving stage.3. The results of Mt135chloroplast gene expression analysis showed40differently expressedgenes identified between albino plants and wide type, including18genes up-regulated and22down-regulated. Functions of these genes were related with proteins responding photoreaction, enzymesof energy metabolism in chloroplast, ribosome biogenesis and tRNA biosynthesis. The alteration trendsof13up-regulated genes detected in the striped plants were similar to those in the albino seedlings.Among these genes, gene families of psb, psa, and ycf, structural proteins of light system II and I, weredown-regulated significantly, genes encoding ribosomal protein subunits were altered, especiallyexpressions of gene rps14encoding ribosomal protein subunit and23S rDNA encoding23S rRNA weresignificantly reduced. It was concluded that the chlorophyll-deficient trait of Mt135was resulted fromthe altered expression of genes related with proteins responding photoreaction, enzymes of energymetabolism in chloroplast, ribosome biogenesis and tRNA biosynthesis.