Preliminery Functional Analysis Of Gene OsSIG2A In Rice (Oryza Sativa L.)

Chloroplasts are the most important organelles in the process of photosynthesis.Although they have their own genomes,the introduction of nuclear proteins to provide the functional and material basis is needed for their development.In this study,a mutant with leaf color-deficient was investigated.The mutant showed albinism phenotype with low photosynthetic content and blocked chloroplast before the three-leaf stage.We isolated the target gene OsSIG2A by map-based cloning and explored its biological function.The main results are as follows:（1）The mutant showed albinism phenotype,with reduced pigment content and incomplete chloroplast structure before the two-leaf stage.At the later three-leaf stage,the leaf phenotype turned light green,which was close to the wild type,and the chloroplast pigment content and structural defects decreased.（2）The mutant albinism phenotype is controlled by a pair of recessive nuclear gene（OsSIG2A）.By map-based cloning,we located the target gene within the 185 kb region of the long arm of the chromosome 11.Sequencing revealed that the mutant gene was replaced by T at the 1493rd base from ATG on the second exon.Transgenic complementation verified LOC_Os11g26160 as the target gene,named OsSIG2A（Oryza Sativa L.Sigma Factor/δ2A）according to previous studies.The gene encoded a plastid RNA polymerase（PEP）,similar to the bacterial typeδ⁷⁰,which was expressed mainly in leaves and located in chloroplasts.（3）OsSIG2A affected the expression of PEP-dependent genes of plastid RNA polymerase during pigment synthesis and photosynthesis.Transcription level analysis found that pigment expression genes were significantly down-regulated in mutants before the two-leaf stage compared with the wild type,and plastid genes expression were also down-regulated simultaneously,while most nuclear-encoded plastid genes were up-regulated.