RESUMO
BACKGROUND: Rice grain production is susceptible to a changing environment that imposes both biotic and abiotic stress conditions. Cold episodes are becoming more frequent in the last years and directly affect rice yield in areas with a temperate climate. Rice is particularly susceptible to cold stress during the reproductive phase, especially in anthers during post-meiotic stages which, in turn, affect pollen production. However, a number of rice cultivars with a certain degree of tolerance to cold have been described, which may represent a good breeding resource for improvement of susceptible commercial varieties. Plants experiencing cold stress activate a molecular response in order to reprogram many metabolic pathways to face these hostile conditions. RESULTS: Here we performed RNA-seq analysis using cold-stressed post-meiotic anther samples from a cold-tolerant, Erythroceros Hokkaido (ERY), and a cold-susceptible commercial cultivar Sant'Andrea (S.AND). Both cultivars displayed an early common molecular response to cold, although the changes in expression levels are much more drastic in the tolerant one. Comparing our datasets, obtained after one-night cold stress, with other similar genome-wide studies showed very few common deregulated genes, suggesting that molecular responses in cold-stressed anthers strongly depend on conditions and the duration of the cold treatments. Cold-tolerant ERY exhibits specific molecular responses related to ethylene metabolism, which appears to be activated after cold stress. On the other hand, S.AND cold-treated plants showed a general downregulation of photosystem I and II genes, supporting a role of photosynthesis and chloroplasts in cold responses in anthers, which has remained elusive. CONCLUSIONS: Our study revealed that a number of ethylene-related transcription factors, as putative master regulators of cold responses, were upregulated in ERY providing promising candidates to confer tolerance to susceptible cultivars. Our results also suggest that the photosynthesis machinery might be a good target to improve cold tolerance in anthers. In summary, our study provides valuable candidates for further analysis and molecular breeding for cold-tolerant rice cultivars.
RESUMO
Rice is one of the main food crops in the world. In the near future, yield is expected to be under pressure due to unfavorable climatic conditions, such as increasing temperatures. Therefore, improving rice germplasm in order to guarantee rice production under harsh environmental conditions is of top priority. Although many physiological studies have contributed to understanding heat responses during anthesis, the most heat-sensitive stage, molecular data are still largely lacking. In this study, an RNA-sequencing approach of heat- and control-treated reproductive tissues during anthesis was carried out using N22, one of the most heat-tolerant rice cultivars known to date. This analysis revealed that expression of genes encoding a number of transcription factor families, together with signal transduction and metabolic pathway genes, is repressed. On the other hand, expression of genes encoding heat shock factors and heat shock proteins was highly activated. Many of these genes are predominantly expressed at late stages of anther development. Further physiological experiments using heat-tolerant N22 and two sensitive cultivars suggest that reduced yield in heat-sensitive plants may be associated with poor pollen development or production in anthers prior to anthesis. In parallel, induction levels of a set of heat-responsive genes in these tissues correlated well with heat tolerance. Altogether, these findings suggest that proper expression of protective chaperones in anthers is needed before anthesis to overcome stress damage and to ensure fertilization. Genes putatively controlling this process were identified and are valuable candidates to consider for molecular breeding of highly productive heat-tolerant cultivars.