P. R. R. Fagundes

Transcriptome profiling of rice seedlings under cold stress

Rice (Oryza sativa L.) is one of the most important species for food production worldwide, besides being an excellent genetic model among the grasses. Cold is one of the major abiotic factors reducing rice yield, primarily affecting germination and reproduction phases. Currently, the RNAseq technique allows the identification of differential expressed genes in response to a given treatment, such as cold stress. In the present work, a transcriptome (RNAseq) analysis was performed in the V3 phase for contrasting genotypes Oro (tolerant) and Tio Taka (sensitive), in response to cold (13°C). A total of 241 and 244M readings were obtained, resulting in the alignment of 25.703 and 26.963 genes in genotypes Oro and Tio Taka respectively. The analyses revealed 259 and 5579 differential expressed genes in response to cold in the genotypes Oro and Tio Taka respectively. Ontology classes with larger changes were metabolic process ~27%, cellular process ~21%, binding ~30% and catalytic activity ~22%. In the genotype Oro, 141 unique genes were identified, 118 were common between Oro and Tio Taka and 5461 were unique to Tio Taka. Genes involved in metabolic routes of signal transduction, phytohormones, antioxidant system and biotic stress were identified. These results provide an understanding that breeding for a quantitative trait, such as cold tolerance at germination, several gene loci must be simultaneously selected. In general, few genes were identified, but it was not possible to associate only one gene function as responsible for the cultivar tolerance; since different genes from different metabolic routes were identified. The genes described in the present work will be useful for future investigations and for the detailed validation in marker assisted selection projects for cold tolerance in the germination of rice.

Above-Optimum Temperature-Induced Differential Photosynthetic and Roots Morphometric Responses in Two Contrasting Rice Genotypes.

Temperature thresholds during the rice (Oryza sativa L.) cycle development have been reported to affect plant metabolism. Therefore, this study aimed to evaluate the effects of the above-optimal temperature on photosynthetic and morphometric parameters in two contrasting irrigated rice genotypes (BRS Querência—sensitive and Nagina 22 (N22)—tolerant). Plants of both genotypes were grown in rhizotrons and always maintained under two temperature conditions: Out—under environmental temperature conditions, and In—rhizotrons inside a plastic structure, which increased the temperature about 3 °C to 5 °C above the external one. In the genotype N22, there was an increase (twofold higher) in CO2 assimilation in plants cultivated under elevated temperature (In). In BRS Querência, the stomatal conductance (gs) and transpiration rate (E) decreased upon high temperature. The rise in the temperature also negatively impacted in the modulated fluorescence parameters in both genotypes. Increases in root dry weight (RDW) and shoot dry weight (SDW) were also observed in the genotype N22 when compared to BRS Querência upon temperature rise. In general, the N22 genotype showed greater response to the above-optimal temperature due to its intrinsic thermotolerance traits over BRS Querência. Thus, N22 appeared as a potential donor of heat tolerance genes aiming to obtain new cultivar to face current global warming.