Transcriptome analysis of drought-tolerant sorghum genotype SC56 in response to water stress reveals an oxidative stress defense strategy

Authors: AZZOUZ-OLDEN, FARIDA - Kentucky State University; HUNT, ARTHUR - University Of Kentucky; Dinkins, Randy

Submitted to: Journal of Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/2020
Publication Date: 4/17/2020
Citation: Azzouz-Olden, F., Hunt, A.G., Dinkins, R.D. 2020. Transcriptome analysis of drought-tolerant sorghum genotype SC56 in response to water stress reveals an oxidative stress defense strategy. Journal of Molecular Biology. 47:3291-3303. https://doi.org/10.1007/s11033-020-05396-5.
DOI: https://doi.org/10.1007/s11033-020-05396-5

Interpretive Summary: Understanding of drought tolerance is a crucial to curtail yield losses inflicted by water stress to crops, yet genetic improvement efforts are challenged by the complexity of the traits that are associated with tolerance. Sorghum is s a good model system to study this trait due to its adaptation to drought conditions and availability of different genotypes displaying different levels of tolerance. The approach has been to subject two closely related genotypes, one sensitive (Tx7000 genotype) and a second tolerant (SC56 genotype), to greenhouse stress conditions and monitor physiological and gene expression, using Next-Gen sequencing, under imposition of stress. The results demonstrated that the tolerant genotype up-regulated a number of genes in pathways that appear to be crucial for biomass accumulation and stress tolerance that enabling this genotype to better survive the stress conditions. This works provides a framework to begin monitoring, either through molecular breeding and selection or manipulation of these genes to enhance water stress tolerance.

Technical Abstract: Background: Drought tolerance is a crucial trait to curtail the yield loss inflicted by water stress to crops, yet genetic improvement efforts are challenged by the complexity of the character. Sorghum’s adaptation to abiotic stress, genotypic variability and relatively small genome make it a model crop to dissect the molecular basis of drought tolerance. One efficient approach to this question is the use of differential transcriptome analysis, which provides a snapshot of the processes underling drought response as well as genes that might be determinants of the tolerance trait. Results: RNA-seq was applied to SC56, a sorghum line contrasting in its drought tolerance with Tx7000. The differential expression analysis revealed unambiguous genotypic disparities, including a massive increase of upregulated transcripts in SC56. Concomitantly, Gene Ontology enrichment showed that SC56 outperformed biologically in wet conditions, as it upregulated processes driving growth and guarantying homeostasis. The drought tolerance of SC56 seems to be an intrinsic trait through the overexpression of stress tolerance genes in wet conditions, notably acting in defense against oxidative stress (SOD1, SOD2, VTC1, MDAR1, MSRB2, and ABC1K1). Under drought, SC56 enhanced its transmembrane transport and maintained growth-promoting processes similar to those implemented under optimal conditions. SC56 also appears to preserve its biological function, under straining condition, by relying on known stress tolerance genes heightening the antioxidant capacity (SOD1, RCI3, VTE1, UCP1, FD1 and FD2), regulatory factors (CIPK1 and CRK7), and repressors of premature senescence (SAUL1). Of the stress tolerance genes overexpressed under both wet and drought conditions, DHAR2 might be a key determinant of drought tolerance since its role in recycling ascorbic acid was reported to be directly linked to protection against ROS-mediated damage, positive effects on photosynthetic activity, higher rate of plant growth and delayed leaf aging. Conclusion: the differential expression analysis uncovered bioprocesses which upregulation enables SC56 to be a better accumulation of biomass, and connects the drought tolerance trait to key stress tolerance genes, making this genotype a judicious choice for isolation of tolerance genes.