Map-based Cloning And Functional Analysis Of DPW3 (Defective Pollen Wall3) Required For Sporopollenin Deposition In Rice Pollen Exine

Rice is one of the most important crops and the pollen fertility directly determines yield of rice.To study on molecular mechanism of pollen development can not only increase production but also provide theoretical basis about male sterile.Our lab established a rice mutant library by treating japonica seeds with 60Coγ-radiation.In this study,we obtained a recessive male sterile mutant dpw3 which is controlled by a single nuclear gene from the mutant library.We identified DPW3 gene by map-based cloning.The mutant phenotype and gene expression pattern were analyzed.Phenotypic observation indicated that dpw3 mutant anther is much smaller than that of wild type.Pollen abortion is the result of failure in starch accumulation,which is caused by the defective sporopollenin deposition in pollen exine.The pollen exine can not form protective sealing structure because of disordered localization of tectum,bacula and nexine.Abnormality in pollen exine caused by sporopollenin deposition variation may infect pollen fertility.Metabolomic analysis found that the amount of cutin and wax is significantly decreased in dpw3 anthers,indicating that the mutation of DPW3 indirectly affects the formation of cutin and wax in the mutant anther.We isolate DPW3 gene by using a map-based cloning approach.DPW3 genome region is deleted in the mutant and dpw3 is a null allele.A wild type DPW3 genomic fragment is able to rescue dpw3 mutant phenotype,confirming that the male sterility of dpw3 is caused by the deletion of DPW3.DPW3 gene encodes a lipid transfer protein with a LTP domain.Phylogenetic analysis showed that DPW3 and its homologs only exist in grass family but not in other plants,indicating that DPW3 belongs to a grass specific LTP gene family.Further analysis showed that DPW3 is specifically expressed in anther.The transcripts of DPW3 can be detected in microspore mother cells,meiocytes and dyad cells during Stage6 and Stage8a.No expression is observed in the tapetum and tetrads.Preliminary result showed that DPW3 is located in cytoplasm of tetrads and young microspores at later stages.Our study identified a novel gene involved in pollen wall formation in rice and provided new clues to understand the molecular mechanism controlling pollen exine patterning.