Phenotypic Analysis And Map-Based Gene Cloning Of High Tillering And Dwarf Mutants

Rice is one of the most important grain crops in the world, and then it is an important goal to breed high yielding rice varieties. The shoot branching is an key factor on determining grain yield of rice. Strigolactones(SLs) is a group of novel plant hormones, playing an important role in controlling the shoot branching of plant. In this study, mutant s2-69 as material was studied in following aspects: analyzation of mutant phenotype, determination of mutation gene ZEBRA2 by the way of map-based cloning, analyzation of gene expression pattern, subcellular Localization analysis of the ZEBRA protein and how ZEBRA2 effect the SLs biosynthesis. The results are as follows:(1)The mutant s2-69 presents high tillering and dwarf phenotype and leaf variegation phynotype;(2)Fine-mapping showed that the mutation site occurred in first exon of the ZEBRA2 gene. A change of a nucleotide(from G to A) that converts 77 th amino acid from glycine to arginine. Besides, we have detected three allelic mutants, named s1-62, s1-115, s1-167 A respectively. ZEBRA2 encodes a carotenoid isomerase(CRTISO), a key enzyme catalyzing conversion of cis-lycopene to all-trans-lycopene in carotenoid biosynthesis;(3)Both RT-PCR and ZEBRA2-promoter-β-glucuronidase(GUS) transgenic rice indicates that ZEBRA2 mainly expressed in mesophyll cells.(4) Subcellular Localization analysis shows that ZEBRA protein was localization in chloroplasts;(5) GR24 treatment of rice seedling indicates that s2-69 is a SLs sensitive mutant. The measurement of epi-5DS shows that the strigolactone content was decreased in the mutant s2-69. All together, the SLs biosynthesis was impaired in mutant s2-69;(6) Carotenoid components content were measured by HPLC which was carried out using the leaf of the wide-type and s2-69 mutant, showing that the carotenoid components content, measured in this study, were changed. The level of the β-carotenoid(precursor of SLs synthesis) of s2-69 mutant was decreased, indicating that ZEBEA2 is involved in effecting the SLs biosynthesis. s2-69 mutant exhibits the characteristic leaf variegation phenotype and decreased level of lutein, the xanthophyll that is essential for efficient chl triplet quenching. We conclude that ZEBRA2 is involved in photoprotection in rice.