Genome-wide identification, expression analysis, and functional study of the GRAS transcription factor family and its response to abiotic stress in sorghum [Sorghum bicolor (L.) Moench].

Background: GRAS, an important family of transcription factors, have played pivotal roles in regulating numerous intriguing biological processes in plant development and abiotic stress responses. Since the sequencing of the sorghum genome, a plethora of genetic studies were mainly focused on the genomic information. The indepth identification or genome-wide analysis of GRAS family genes, especially in Sorghum bicolor, have rarely been studied.

Results: A total of 81 SbGRAS genes were identified based on the S. bicolor genome. They were named SbGRAS01 to SbGRAS81 and grouped into 13 subfamilies (LISCL, DLT, OS19, SCL4/7, PAT1, SHR, SCL3, HAM-1, SCR, DELLA, HAM-2, LAS and OS4). SbGRAS genes are not evenly distributed on the chromosomes. According to the results of the gene and motif composition, SbGRAS members located in the same group contained analogous intron/exon and motif organizations. We found that the contribution of tandem repeats to the increase in sorghum GRAS members was slightly greater than that of fragment repeats. By quantitative (q) RT-PCR, the expression of 13 SbGRAS members in different plant tissues and in plants exposed to six abiotic stresses at the seedling stage were quantified. We further investigated the relationship between DELLA genes, GAs and grain development in S. bicolor. The paclobutrazol treatment significantly increased grain weight, and affected the expression levels of all DELLA subfamily genes. SbGRAS03 is the most sensitive to paclobutrazol treatment, but also has a high response to abiotic stresses.

Conclusions: Collectively, SbGRAs play an important role in plant development and response to abiotic stress. This systematic analysis lays the foundation for further study of the functional characteristics of GRAS genes of S. bicolor.