Transcriptomic analysis of three Sorghum bicolor landraces following progressive water stress and re-watering

Background: Sorghum bicolor is a remarkably drought tolerant cereal crop. Its natural biodiversity that enables this tolerance has developed in sub-Saharan Africa. The sequencing of the sorghum genome in 2009 has expedited research of this crop which has also been proposed as a model C4 cereal crop for genomics. In this study, the genetic response mechanisms involved in sorghums’ tolerance to progressive water deficit and moderate re-watering were investigated in three previously uncharacterized South African landraces (designated: LR5, LR6 and LR35) using cDNA microarrays comprising 35 899 transcript probes. Results: Across the three landraces, significant differential expression of 1 797 genes, including 264 genes with currently unknown functions, were altered in response to progressive water stress and re-watering. The modulated sorghum genes had homology to proteins involved in growth, regulation, and protection. Gene ontology analysis identified significant enrichment of 26 genes involved in the ‘response to abiotic stimulus’ GO category in LR6 during severe stress. The expression of USP responded to progressive water stress and moderate re-watering in LR6 and LR35. Moreover, our results indicate a putative role for β-alanine betaine biosynthesis in drought tolerance of sorghum. Conclusions: This study identified the drought responsive gene complement of three previously uncharacterized South African sorghum landraces. Each landrace is a distinct genotype and similar responses to water deficit and re-watering were not expected. Functional characterizations of some of the differentially expressed genes found in this study may be used as possible targets for marker-assisted breeding or transgenic initiatives for sorghum and, other closely related crop species. 3 Sorghum landraces, 3 stress conditions per landrace, 3 biological replicates per stress condition, 3 controls per landrace