Fine Mapping Of AL13(T), A Gene For Albino And Identification Of Its Candidate In Rice

Rice leaf color mutants are ideal materials for studying photosynthetic system structure and function, chlorophyll biosynthesis and regulation mechanism. A rice leaf color mutant named al13(t) was obtained from a japonica variety, Zhonghua11, and died in3leaf stage, Compared with the wild type, the morphological characters, genetic analysis, photosynthetic pigment contents and the chloroplast ultra-microstructure were studied. Meanwhile the AL13(t) were analyzed by mapping, cloning and other molecular biology techniques. The main results were as follows:1The morphology analysis of the al13(t)The albino and lethal mutant al13(t) showed albino color at seedling stage, and died after three-leaf stage.2The ultra-structure analysis of the al13(t) chloroplastThe chloroplast structure of the al13(t) was significantly different from that of the control plant Zhonghuall. There were less chloroplasts in the mutant and their shapes were irregular. We found that rice albino mutant al13(t) had no thylakoid inside and the chloroplast only with some Osmiophilic vesicles. The biogenesis of chloroplast were divided into three stages:the stage of proplast; the biogenesis of single thykoid and the biogenesis of grana under electron microscope.The development of al13(t) mutant chloroplast stopped at the stage of proplast.3. Photosynthetic characteristics analysis of the al13(t)The chlorophyll a, chlorophyll b, total chlorophyll and carotenoid contents were significantly less than that of the wild type, which were almost undetectable;The mutant al13(t)had a negative net photosynthetic rate;4. Genetic analysis of the AL13(t)The combination of Jinghuil crossed with the al13(t) was used to build F1group. The leaf color of F1progenies represented normal green. In the F2progenies, the segregation ratio of normal green leaf blades(308) to yellow blades(120) fitted the expected ratio of3:1(χ2=1.93<χ20.05=3.84), which suggested that the albino trait of al13(t) was controlled by one pair of recessive nuclear gene.5. Fine-Mapping of the AL13(t) geneA genetic linkage map was constructed using a large F2mapping population derived from a cross between the mutant and an indica variety, Jinghui1.The AL13(t) gene was mapped between the markers R8008and R1243. The candidate region was then further delimited to87Kb between the markers R5840-4and RDraI56417which were on two overlapping BACs by usingl8new developed molecular markers. A total of12genes were found at this interval. By analyzing and sequencing the candidate genes in this genomic region, it was found that there was a13nucleotide deletion in exon of LOC_Os07g07620gene encoding a PPR gene in the al13(t) mutant, which caused a frame-shift mutation and in loss of function of the gene. In addition, previous studies have shown that many albino mutants of seedlings are related to PPR proteins. Hence, we presume that the PPR gene is the candidate for al13(t).