Comprehensive Genome-wide Analysis Of The GRAS Transcription Factor Family In Tomato And Functional Identification Of SlGRAS24

GRAS proteins are plant-specific transcription factors that involve in various developmental processes, including meristem maintenance, root radial patterning, light signaling, phytohormone signaling, and abiotic/biotic stress response. By far, GRAS gene family has been genome-wide explored in several plant species such as Populus,Arabidopsis, rice, Chinese cabbage,Prunus mume, andpine. However, little is known about this gene family in tomato(Solanum lycopersicum), the most important model plant for crop species with fleshy fruits. In this regard, several works were completed in this thesis:(1)53 GRAS genes were identified and renamed based on tomato whole-genome sequence and their respective chromosome distribution except 19 members were kept as their already existed name. Multiple sequence alignment showed typical GRAS domain in these proteins. Phylogenetic analysis of GRAS proteins from tomato,Arabidopsis,Populus,P.mume, and Rice revealed that SlGRAS proteins could be divided into at least 13 subfamilies. SlGRAS24 and SlGRAS40 were identified as target genes of miR171 using 5'-RACE(Rapid amplification of c DNA ends). qRT-PCR analysis revealed tissue-/organ- and development stage-specific expression patterns of SlGRAS genes. And their expression patterns in response to different hormone and abiotic stress treatments were also investigated.(2) SlGRAS24 over-expressing transgenic plants(OE) displayed pleiotropic phenotypes, including dwarf plant,smaller leaf size, delayed flowering time, ectopic axillary bud, decreased primary root length as well as lateral root number, and declined fruit set ratio. Both qRT-PCR analysis of SlGRAS24 and histochemical analysis of ?-glucuronidase(GUS) activity in transgenic plants expressing pGRAS24::GUS exhibit specific distributions in vegetative and reproductive tissues.(3)“GARE” and “AuxRE”cis-element were found in the promoter region ofSlGRAS24, and either GA3 or IAA treatment on WT tomato and pGRAS24::GUS transgenic tomato led to increased expression of SlGRAS24.Most GA/auxin-related genes were down-regulated in SlGRAS24-OE seedlings, and different GA3 or IAA responsiveness was observed;SlGRAS24-OE plants showed increased endogenous GA3 and IAA content.Altered sensitivity to exogenous GA3 and IAA application were found in SlGRAS24-OE plants, which suggest its potential role in mediating cross-talk of these two hormones.(4) Cross-fertilization assay,TTC staining, and histology analysis results demonstrated that the declined fruit set, partial arrested fuit/seed development were mainly caused by fewer viable pollen grains in SlGRAS24-OE mature flowers; Meanwhile, RNA-seq in mature flowers displayed differential expression of genes associated with pollen development, hormone signaling.Both histology analysis and qRT-PCR results showed that the cell division and cell expansion of SlGRAS24-OE fruits were severly inhibited.Together, this study provides the first comprehensive analysis of GRAS gene family in the tomato genome. The data will undoubtedly be useful for better understanding the potential functions of GRAS genes, and their possibleroles in mediating hormone cross-talk and abiotic stress in tomato as well as in some other relative species. In addition, through phenotypic observation and analysis of transgenic tomato palnts, we find that SlGRAS24 gets involved in auxin-gibberellin crosstalk and plays an important role during late stamen development, enhancing our knowledge about the underlying molecular mechanisms of these two physiological processes.