Expression of drought tolerance genes in tropical upland rice cultivars (Oryza sativa)

Gene expression related to drought response in the leaf tissues of two Brazilian upland cultivars, the drought-tolerant Douradao and the drought-sensitive Primavera, was analyzed. RNA-seq identified 27,618 transcripts in the Douradao cultivar, with 24,090 (87.2%) homologous to the rice database, and 27,221 transcripts in the Primavera cultivar, with 23,663 (86.9%) homologous to the rice database. Gene-expression analysis between control and water-deficient treatments revealed 493 and 1154 differentially expressed genes in Douradao and Primavera cultivars, respectively. Genes exclusively expressed under drought were identified for Douradao, including two genes of particular interest coding for the protein peroxidase precursor, which is involved in three distinct metabolic pathways. Comparisons between the two drought-exposed cultivars revealed 2314 genes were differentially expressed (978 upregulated, 1336 downregulated in Douradao). Six genes distributed across 4 different transcription factor families (bHLH, MYB, NAC, and WRKY) were identified, all of which were upregulated in Douradao compared to Primavera during drought. Most of the genes identified in Douradao activate metabolic pathways responsible for production of secondary metabolites and genes coding for enzymatically active signaling receptors. Quantitative PCR validation showed that most gene expression was in agreement with computational prediction of these transcripts. The transcripts identified here will define molecular markers for identification of Cis-acting elements to search for allelic variants of these genes through analysis of polymorphic SNPs in GenBank accessions of upland rice, aiming to develop cultivars with the best combination of these alleles, resulting in materials with high yield potential in the event of drought during the reproductive phase.