Genetic Analysis And Gene Mapping On Yellowing Mutant Jw22in Rice

Leaf color mutant was a familiar mutant type in nature, which attracted much attention for a long time because of its visible phenotype and discernable character. Chlorophyll is the important pigment involved in photosynthesis in plant chloroplasts, biosynthesis of chlorophyll is a very complicated process. When the gene regulating development and metabolism of chlorophyll mutated, the leaf color of plant will change correspondingly. In rice, many chlorophyll deficient mutants had been find consists of eight classes on the basis of their phenotypes:albina, xanthan, virids, jade-white, green-white, green-yellow, yellow-green and striata. Chlorophyll-deficit mutants not only play an important role in studying the photosynthesis, biosynthesis of chlorophyll, genetic differentiation and development of chloroplast, but also serve as a marker to kick out fulse hybrids in utilizing rice heterosis.In this paper, a yellowing mutant, designated as "jw22" was identified from Indica variety zhong17B. The morphological characters, agricultural traits, physiological characteristics and chloroplast ultrastructure of this yellowing mutant were studied. Genetic action of the yellowing character was analyzed by using the F1and F2progenies from jw22crossed with green original parent02428, a normal leaf-color variety. Furthermore, this mutant gene was mapped with molecular markers. The results are as follows:1. Phenotype of jw22The phenotype character of yellowing mutant jw22is that leaf color is yellow in its whole growth period. Furthermore, compared with the wild type, the number of tillers reduces and growth stage prolongs. When the plants mature, the jw22mutant was much shorter than wild-type.2. Physiological characteristics of jw22The photo synthetic pigment content of jw22decreased significantly at three different growth stages, seedling, tillering and heading stage, compared with that of zhongl7B.The chlorophyll content decreased by44.18～66.83%.The carotenoid content decreased by15.87～19.35%.The chlorophyll a and chlorophyll b contents decreased by37.76～60.08%and61.07～77.46%, respectively.The decreased degree of chlorophyll content was higher than that of carotenoid content, and the decreased degree of chlorophyll b content was higher than that of chlorophyll a content. So, it was supposed that large degree of decrease in chlorophyll b content would be the main reason leading to the appearance of yellowing character.3. Ultrastructure of the chloroplast in the mutant jw22The ultrasrructure of choloroplast in jw22was observed with transmission electron microscope. As a result, the inner structure of the chloroplast changed evidently in jw22, the grana lamella became loose.The number of starch granules reduced and it’s structure changed. Beside this, the lipopigment particles increased and accumulated.4. Genetic analysis of mutant jw22The combinations of jw22crossed with a normal green variety02428were used in genetic analysis. The result showed that leaf color of F1progenies represented normal green, and segregation ratio of normal green to yellowing fietted the expected ratio of3:1in F2population, which suggested that the yellowing trait of jw22was controlled by one pair of recessive nuclear gene.5. Gene mapping of the mutant jw22The F2population of jw22/02428was used as the preliminary mapping population. The genomic DNA of both parent were amplified with661pairs of primers of molecular markers well-distributed on12chromosomes of rice,203polymorphic markers were obtained between jw22and02428. The mutant gene was preliminary located on chromosome3between RM22and RM282. The genetic distances from the target gene to the markers RM22and RM282were2.9cM and9.1cM, respectively. Then F2and F2:3were used as large mapping population, the mutant gene was mapped within a53kb interval between JW22-10and JW22-36finally. The gene was considered to be a new yellowing mutant gene in rice, and so temporarily designated as chl14(t).6. Candidate gene prediction The target region was analyzed with RiceGAAS (http://ricegaas.dna.affrc.go.jp) and14opening reading frames (ORF) were predicted. Realated with the mutant trait, One ORF was selected in the fourteen. It’s encodes Mg-protoporphyrin IX chelatase subunit H, an important gene involved in chlorophll biosynthesis.Therefore, this ORF is most probably the candidate gene for chll4(t).