Resposta morfofisiológica de Setaria viridis ao estresse de frio, e prospecção e caracterização de genes responsivos ao frio, diferencialmente expressos em Elaeis guineensis

Abstract

Palm oil trees (Elaeis guineensis) are important crops for the Brazilian strategy of diversification of raw materials to be used by the biodiesel industry. In this sense, the expansion of the cultivation area beyond the Amazon Region can consolidate its participation in the biodiesel production chain. However, as this crop goes South in Brazil, it will undoubtedly face new challenges such as cold stress. Learning more about the morphological, biochemical and genetic responses to this abiotic stress is fundamental in order to develop cold tolerant palm oil genotypes. This study had two main objectives: a) to carry out an initial identification and a preliminary annotation of the E. guineensis genes whose expression changes significantly when this species is subjected to cold stress; and b) to characterize the response of two accessions of Setaria viridis (A.10 and AST) to cold stress, in order to know if these accessions could be used as model plants for reverse genetics studies aiming the validation of cold tolerant candidate genes. S. viridis plants, both in the vegetative and reproductive stages of development, were subjected to cold stress in a gradual (temperature reduction of 5ºC every 24h; starting at 25°C) or abrupt (instantaneous reduction from 25 to 0°C) manner, and maintained at 0°C for periods of 3, 5 and 10 days. To evaluate the response of Setaria plants to cold stress, data related to gas exchange and chlorophyll fluorescence were collected. Data related to biomass production were also collected at the end of the plant development cycle. In both abrupt and gradual regimes, photosynthesis reached zero only when the temperature reached 0°C. It was observed that the longer the duration of stress, the more difficult the recovery, regardless the way in which the plant was subjected to cold. As for biomass production, the plant had a better recovery when the stress occurred in the vegetative phase. The results showed that S. viridis is cold tolerant. Therefore, accessions A10.1 and AST of this species cannot be used as model plants for the validation of candidate genes for cold tolerance. The Galaxy web-based public platform for bioinformatics was used to analyze the quality and differential expression of RNA-Seq data from palm oil trees subjected to cold stress. A total of 190 transcripts, in which the difference in the level of expression between control and the stressed plants was statistically significant (p-value> 0.01), were identified; 92 transcripts were up regulated (eight or more times) when the plant is subjected to cold, and 98 were down regulated (eight or more times). The genes from the E. guineensis (EG5) genome to which these transcripts aligned were identified and their sequences (mRNA) were aligned (BLASTx) against the S. viridis genome available from the NCBI.