Project description:Rice in tropical and sub-tropical areas is often subjected to cold stress at the seedling stage resulting in poor growth and yield loss. In general, japonica rice has stronger cold tolerance (CT) than indica rice. However, several favorite alleles for CT exist in indica rice and can be used to enhance CT under japonica background. Genome-wide gene expression profiling is the efficient way to decipher the molecular genetic mechanism of CT enhancement and provide valuable information for the CT improvement in rice molecular breeding. In this study, the transcriptome of a CT introgressed line (IL) K354 and its recurrent parent C418 under cold stress were comparatively analyzed to explore the possible CT enhancement mechanism of K354.Totally 3184 differentially expressed genes (DEGs) including 195 transcription factors were identified in both lines under cold stress, about half of them were commonly regulated, which were involved in the major cold responsive pathways including OsDREB1s regulon. The K354-specific cold-induced DEGs were mainly related to stimulus response, cellular cell wall organization, and microtubule-based movement process compared with commonly cold-induced DEGs by GO analysis. Moreover, 296 constitutive DEGs with significantly different transcription level between C418 and K354 were detected under both control and cold stress conditions. K354-specific cold-regulated and constitutive DEGs jointly account for the CT improvement of K354. Pathway analysis unraveled up-regulation of starch and sucrose metabolism in both genotypes and presumably weaker defense response to stress in K354 than C418 under cold stress. Candidate genes prediction based on previous putative CT genetic networks revealed genotype-dependent CT enhancement mechanism in CT IL K354 vs recurrent parent C418, including Sir2, OsFAD7, OsWAK112d, and PCD related genes, etc.We propose a hypothesis of the CT enhancement mechanism in rice based on the results in present study. Firstly, a number of cold-regulated genes are able to express constitutively at high level or absent under control condition for standing by the arrival of cold stress. Next, under cold stress slower perception of stress signal from the more cold-tolerant membrane can postpone the activation of defensive system which may have possible negative effects on rice growth. Then, PCD will be launched to sacrifice a few cells for maintaining the basal growth of most cells. Finally, the protective responses on multiple aspects of cold damage will be postponed because of delayed several cold-defensive pathways (i.e. OsDREB1C regulon). It might explain why the recovery capacity of K354 from cold stress to control condition is stronger than C418. The CT enhancement mechanism can be regarded as the possible way to improve CT of japonica rice using indica germplasm in rice breeding program.

Project description:Rice in tropical and sub-tropical areas is often subjected to cold stress at the seedling stage resulting in poor growth and yield loss. In general, japonica rice has stronger cold tolerance (CT) than indica rice. However, several favorite alleles for CT exist in indica rice and can be used to enhance CT under japonica background. Genome-wide gene expression profiling is the efficient way to decipher the molecular genetic mechanism of CT enhancement and provide valuable information for the CT improvement in rice molecular breeding. In this study, the transcriptome of a CT introgressed line (IL) K354 and its recurrent parent C418 under cold stress were comparatively analyzed to explore the possible CT enhancement mechanism of K354.Totally 3184 differentially expressed genes (DEGs) including 195 transcription factors were identified in both lines under cold stress, about half of them were commonly regulated, which were involved in the major cold responsive pathways including OsDREB1s regulon. The K354-specific cold-induced DEGs were mainly related to stimulus response, cellular cell wall organization, and microtubule-based movement process compared with commonly cold-induced DEGs by GO analysis. Moreover, 296 constitutive DEGs with significantly different transcription level between C418 and K354 were detected under both control and cold stress conditions. K354-specific cold-regulated and constitutive DEGs jointly account for the CT improvement of K354. Pathway analysis unraveled up-regulation of starch and sucrose metabolism in both genotypes and presumably weaker defense response to stress in K354 than C418 under cold stress. Candidate genes prediction based on previous putative CT genetic networks revealed genotype-dependent CT enhancement mechanism in CT IL K354 vs recurrent parent C418, including Sir2, OsFAD7, OsWAK112d, and PCD related genes, etc.We propose a hypothesis of the CT enhancement mechanism in rice based on the results in present study. Firstly, a number of cold-regulated genes are able to express constitutively at high level or absent under control condition for standing by the arrival of cold stress. Next, under cold stress slower perception of stress signal from the more cold-tolerant membrane can postpone the activation of defensive system which may have possible negative effects on rice growth. Then, PCD will be launched to sacrifice a few cells for maintaining the basal growth of most cells. Finally, the protective responses on multiple aspects of cold damage will be postponed because of delayed several cold-defensive pathways (i.e. OsDREB1C regulon). It might explain why the recovery capacity of K354 from cold stress to control condition is stronger than C418. The CT enhancement mechanism can be regarded as the possible way to improve CT of japonica rice using indica germplasm in rice breeding program. In this study, the specific gene expression patterns of two genotypes (C418 and K354) at 2h, 6h, 12h, 24h and 48h during cold stress treatment (4 C) and control were characterized by using the Affymetrix rice microarray platform.

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