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Expression data for heat tolerant and susceptible cultivars of indica rice

ABSTRACT: Heat stress along with other abiotic stresses is one of the major factors affecting crop health and overall yield in a tropical country like India. Thus, there is an urgent need to understand the dynamics of heat responsiveness at the molecular as well as physiological level. Fortunately, India has a number of indigenous varieties that show tolerance to extremes in temperature during the scorching summer months. The cultivar Annapurna is a fast growing dwarf variety of rice that is heat tolerant while the most widely grown indica rice in South and Southeast Asia, IR64, is susceptible to high temperatures. These two cultivars present an excellent opportunity to study the differences in response to heat stress, and, thereby help in elucidating the genes involved in conferring tolerance to high temperature. The present study involves transcript profiling of the two cultivars, Annapurna (tolerant) and IR64 (susceptible) under both control and heat stressed conditions.

ORGANISM(S): Oryza sativa Oryza sativa Indica Group

PROVIDER: GSE41648 | GEO | 2021/07/26

REPOSITORIES: GEO

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Project description:Purpose: understanding the complex genetic control of heat tolerance can be reached using whole transcriptome sequencing (RNA-seq) that is currently the most powerful tool to identify genes differentially regulated. Heat responses differ greatly between sensitive and tolerant genotypes, mainly in terms of the amount of genes and pathways involved in the response and differences in the expression level of constitutive genes in many pathways. The present study aims to compare the molecular response of Brazilian flooded rice cultivars with variable sensitivity to heat stress at anthesis stage and to discuss the possible processes involved in heat tolerance. Methods: Panicle mRNA profiles of cultivars IRGA 428 (sensitive) and BR-IRGA 409 (tolerant) were generated by deep sequencing, in triplicate (each replicate is composed of two plants), under three days of heat stress and control condition at anthesis stage, using Illumina Hiseq 2500. The sequence reads from each sample that passed quality filters were mapped independently, generating contigs that were aligned with the reference genome sequences in rice (cv. MH63-indica). The transcripts were analyzed at the expression level with statistic test (EdgeR – Rstudio) to identify the significant changes in the expression level of the genes for each treatment condition and cultivar follow by identification of metabolic pathways (MapMan and Cytoscape) based on different programs. Results: Using an optimized data analysis workflow, we identified 16,871 transcripts in the rice spikelet of sensitive and tolerant cultivars with HISAT workflow. Using filtered and aligned reads, transcript levels were used to find differentially expressed genes (DEGs) at different thermal condition and cultivars. We identified 2,064 genes for BR-IRGA 409 and 1,078 genes for IRGA 428 that showed a significant change in expression in response to heat stress (LogFC ≥0.5 and adjusted p-value <0.001). When it was examined the multi-factor responsive genes, that is genes with an interaction between cultivar and heat stress (multi-factor analysis - cultivars vs control and high temperature), it was identified 65 DEGs in response to heat stress (LogFC ≥0.5 and adjusted p-value <0.001). Comparison of our data set with other RNA-seq studies shows a significant overlap in heat responsive genes (hypergeometric enrichment test). This core set of genes common among RNA-seq studies indicates that it may be associated with basal response to heat. In the present study, genes related to light reaction pathway were induced in the panicle of the cultivar IRGA 428, while these genes in cultivar BR-IRGA 409 were already expressed highly in control conditions. The basal level of these genes in BR-IRGA 409 was as high as the heat-induced level in the sensitive IRGA 428. Photosynthesis is known to occur in rice panicles, but little has been reported about the photosynthetic characteristics of such panicles. To cope with heat stress, plants have developed a sophisticated mechanism to repair photosystem damage. Therefore, in IRGA 428 the induction of these genes suggests the activation of a repair mechanism to reverse damage on the photosynthetic apparatus caused by the heat stress. The difference in basal levels of the photosynthetic genes may be a contributing factor to the differences in spikelet fertility between the cultivars under heat stress. Conclusion: This is the first study to evaluate the heat tolerance of Brazilian rice cultivars. In panicle tissue, most canonical heat responsive genes, such as HSF family, small HSP family and FKBP family, show a similar response in both Brazilian cultivars, despite the fact that these cultivars have not been specifically selected for heat tolerance. The response of photosynthetic genes to heat stress is a major difference between the cultivars BR-IRGA 409 and IRGA 428. This study indicates that the higher basal expression of photosynthetic genes in the panicle provides improved spikelet fertility under heat stress. This may provide potential markers that can be used to identify heat tolerant genotypes among rice breeding programs. This study emphasizes that the characterization of heat stress responses in individual cultivars provides insights into both the basic mechanisms of heat response and assists with understanding the complex phenomenon of responses to high temperature stress.

Project description: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, leading to the conclusion 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.

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Expression data for heat tolerant and susceptible cultivars of indica rice

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