SlBBX20 interacts with the COP9 signalosome subunit SlCSN5-2 to regulate anthocyanin biosynthesis by activating SlDFR expression in tomato

Anthocyanins play vital roles in plant stress tolerance and growth regulation.Previously,we reported that the photomorphogenesis-related transcription factor SlBBX20 regulates anthocyanin accumulation in tomato.However,the underlying mechanism remains unclear.Here,we showed that SlBBX20 promotes anthocyanin biosynthesis by binding the promoter of the anthocyanin biosynthesis gene SlDFR,suggesting that SlBBX20 directly activates anthocyanin biosynthesis genes.Furthermore,we found by yeast two-hybrid screening that SlBBX20 interacts with the COP9 signalosome subunit SlCSN5-2,and the interaction was confirmed by bimolecular fluorescence complementation and coimmunoprecipitation assays.SlCSN5 gene silencing led to anthocyanin hyperaccumulation in the transgenic tomato calli and shoots,and SlCSN5-2 overexpression decreased anthocyanin accumulation,suggesting thSlCSN5-2 enhanced the ubiquitination of SlBBX20 and promoted the degradation of SlBBX20 in vivo.Consistently,silencing the SlCSN5-2 homolog in tobacco significantly increased the accumulation of the SlBBX20 protein.Since SlBBX20 is a vital regulator of photomorphogenesis,the SlBBX20-SlCSN5-2 module may represent a novel regulatory pathway in light-induced anthocyanin biosynthesis.

FUNCTIONAL GAIN OF FRUIT NETTED-CRACKING IN AN INTROGRESSION LINE OF TOMATO WITH HIGHER EXPRESSION OF THE FNC GENE

Fruit cracking is a major disorder that affects the integrity of fruit and reduces the commercial value of tomato and other fleshy fruit.Here,we have found a novel fruit'netted-cracking'(FNC)phenotype in tomato introgression line IL4-4 which is present in neither the donor parent(LA0716)nor the receptor parent(M82).An F2 population was generated by crossing IL4-4 with M82 to genetically characterize the FNC gene and this showed that a single dominant gene determined fruit netted-cracking.Further map-based cloning narrowed down the FNC locus to a 230 kb region on chromosome 4.Sequencing and annotation analysis show that FNC(Solyc04 g082540)was the most likely candidate gene.Functional characterization of FNC by overexpressing FNC^c and FNC1^resulted in the fruit netted-cracking phenotype,suggesting that the FNC transcript level results in the functional gain of fruit netted-cracking.These findings were further confirmed by FNC ortholog in netted-cracking pepper and melon,indicating a common regulatory mechanism in different plant species.Furthermore,cytoplasm and nucleus-localized FNC indicates increased expression of genes involved in suberin,lignin,lipid transport and cell wall metabolism.These findings provide novel genetic insights into fruit netted-cracking and offer a way to promote molecular improvement toward cracking resistant cultivars.

Genome-wide Analysis of Plant-specific Dof Transcription Factor Family in Tomato

The Dof （DNA binding with One Finger） family encoding single zinc finger proteins has been known as a family of plant-specific transcription factors. These transcription factors are involved in a variety of functions of importance for different biological processes in plants. In the current study, we identified 34 Dof family genes in tomato （Solanum lycopersicum L.）, distributed on 11 chromosomes. A complete overview of SlDof genes in tomato is presented, including the gene structures, chromosome locations, phylogeny, protein motifs and evolution pattern. Phylogenetic analysis of 34 SlDof proteins resulted in four classes constituting six clusters. In addition, a comparative analysis between these genes in tomato, Arabidopsis （Arabidopsis thaliana L.） and rice （Oryza sativa L.） was also performed. The tomato Dof family expansion has been dated to recent duplication events, and segmental duplication is predominant for the SlDof genes. Furthermore, the SlDof genes displayed differential expression either in their transcript abundance or in their expression patterns under normal growth conditions. This is the first step towards genome-wide analyses of the Dof genes in tomato. Our study provides a very useful reference for cloning and functional analysis of the members of this gene family in tomato and other species.

Silencing GRAS2 reduces fruit weight in tomato

GRAS family transcription factors are involved in multiple biological processes in plants. Here, we report that GRAS2 plays a vital role in regulating fruit weight in tomato （Solanum lycopersicum）. We establish that the expression of GRAS2 was elevated in ovaries and maintained at a constant level in fertilized ovules. Reduction of GRAS2 expression in transgenic plants reduced fruit weight through modulating ovary growth and cell size. At the metabolic level, downregulation of GRAS2 decreased activities of the gibberellic acid biosyn- thesis and signal transduction pathways, leading to insufficient levels of active gibberellic acid during the initial ovary development of tomato. Moreover, genotypic diversity of GRAS2 was consistent with the molecular basis of fruit weight evolution, suggesting that GRAS2 contributes to the molecular basis of the evolution of fruit weight in tomato. Collectively, these findings enhance our understanding of GRAS2 functions, in fruit development of tomato, and demonstrate a strong association between the GRAS gene family and fruit development.