Characterization Of GRAS2 Gene Involved In Fruit Development In Tomato

Tomao(Solanum lycopersicum)is served as one of the typical model plants for the molecular mechanism of the development of fresh fruit,because of its short growth cycle,stable genetic feature,small-scale genome.Several genes related with tomato fruit weight have been cloned by classical biparental crossing-mapping method.As there are some limitations in the classical QTL-mapping method,it is difficult to dissect and research key genes in the mapped fruit weight QTLs.Genome-wide association study could be a powerful complementary method to classical biparental crossing-mapping for rapidly dissecting key genes related with fruit weight in tomato.In this study,we studied tomato fruit weight by a genome-wide association study(GWAS)in the population of 288 accessions,and identified that GRAS2 was an essential regulator of fruit weight in tomato.The important results were shown as belows:1.Nine independent significant peak signals were identified by GWAS on tomato fruit weight.There were four signals tied closely to the reported genes lc,fw3.2,fascinated,fw11.3,demonstrating a reliable data,a reasonable model and a accurate result in this study.In addition,there were other five signals within the region of fw1.2,fw6.3,fw7.3,fw11.1 and fw11.2,respectively,providing an evidence for identifying key genes in these regions.2.GRAS2,the closest gene to significant SNP63492244,was found to be the potential key gene of fw7.3 by analysing the significant signals in the fw7.3 region and combining the result of candidate genes' transgenic plants.The growth of GRAS2-RNAi fruits were found to be restrained,showing a series of phenotypes of smaller floral organs,a restrained growth of early ovary development,thinner pericarp thickness,shrunken cells,less seed numbers,Meanwhile,the plant height of GRAS2-RNAi plants also became shorter,investigating that GRAS2 was essential for plant normal development.3.Transcription analysis showed that GRAS2 had a high expression in the ovary at flowering time.Meanwhile,GRAS2 had a consistent expression at the seed peripheral integument layers,suggesting the special expression stage and expression position were critical to fruit development.GRAS2 was involved in the gibberellin biosynthesis pathsway to induce ovary development.The gibberellin effect to induce ovary development was destroyed in the GRAS2-RNAi lines,leading to a restrained growth of fruit.4.In the genetic molecular level,the diversity of GRAS2 is consistent with the genetic and molecular basis of fruit evolution.The genetic analysis indicated an obvious variation of GRAS2 arose in the evolutionary transition from wild to cherry tomato,rather than an improvement process from cherry tomato to moden big tomatoes.5.There were high similarities of GRAS2 homologous genes in other Solanacea species including pepper and eggplant,which implied that homologous genes might exist similar mechanism.According to GRAS2 function in tomato,it was helpful to reveal the fruit developmental mechanism other Solanacea species such as pepper and eggplant.