Potential Roles of the GRF Transcription Factors in Sorghum Internodes during Post-Reproductive Stages.

Growth-regulating factor (GRF) is a plant-specific family of transcription factors crucial for meristem development and plant growth. Sorghum ( Sorghum bicolor L. Moench) is a cereal species widely used for food, feed and fuel. While sorghum stems are important biomass components, the regulation of stem development and the carbohydrate composition of the stem tissues remain largely unknown. Here, we identified 11 SbGRF-encoding genes and found the SbGRF expansion driven by whole-genome duplication events. By comparative analyses of GRF s between rice and sorghum, we demonstrated the divergence of whole-genome duplication (WGD)-derived OsGRF s and SbGRF s. A comparison of SbGRF s' expression profiles supports that the WGD-duplicated OsGRFs and SbGRF s experienced distinct evolutionary trajectories, possibly leading to diverged functions. RNA-seq analysis of the internode tissues identified several SbGRF s involved in internode elongation, maturation and cell wall metabolism. We constructed co-expression networks with the RNA-seq data of sorghum internodes. Network analysis discovered that SbGRF1 , 5 and 7 could be involved in the down-regulation of the biosynthesis of cell wall components, while SbGRF4 , 6 , 8 and 9 could be associated with the regulation of cell wall loosening, reassembly and/or starch biosynthesis. In summary, our genome-wide analysis of SbGRF s reveals the distinct evolutionary trajectories of WGD-derived SbGRF pairs. Importantly, expression analyses highlight previously unknown functions of several SbGRF s in internode elongation, maturation and the potential involvement in the metabolism of the cell wall and starch during post-anthesis stages.