RESUMO
Cold stress is a major factor affecting rice (Oryza sativa) growth and productivity, limiting its distribution worldwide. Rice production is affected primarily due to its vulnerability to cold stress at seedling stage, as well as reproductive stage leading to spikelet sterility. We report here the analysis of 21 diverse rice genotypes from the USDA mini-core collection for cold tolerance and categorized their tolerance levels on the basis of reduction in growth measured by root and shoot length. The screening identified 12 cold tolerant genotypes from which six tolerant genotypes were characterized at the vegetative stage for cold tolerance and gas-exchange parameters. Two tolerant and two sensitive genotypes were used further for gene expression analysis. Lipid Transfer Protein (LTP) genes showed a clear difference in expression between cold tolerant and sensitive genotypes suggesting that they are good candidates for engineering cold tolerance in rice. Nipponbare was identified as a cold tolerant genotype with stress tolerance mechanism potentially operating via both ABA dependent and independent pathways.
Assuntos
Proteínas de Transporte/genética , Resposta ao Choque Frio/genética , Regulação da Expressão Gênica de Plantas/genética , Oryza/fisiologia , Fotossíntese/genética , Proteínas de Plantas/genética , Genótipo , Oryza/classificação , Especificidade da EspécieRESUMO
Rice (Oryza sativa L.) cultivars show impairment of growth in response to environmental stresses such as cold at the early seedling stage. Locally adapted weedy rice is able to survive under adverse environmental conditions, and can emerge in fields from greater soil depth. Cold-tolerant weedy rice can be a good genetic source for developing cold-tolerant, weed-competitive rice cultivars. An in-depth analysis is presented here of diverse indica and japonica rice genotypes, mostly weedy rice, for cold stress response to provide an understanding of different stress adaptive mechanisms towards improvement of the rice crop performance in the field. We have tested a collection of weedy rice genotypes to: 1) classify the subspecies (ssp.) grouping (japonica or indica) of 21 accessions; 2) evaluate their sensitivity to cold stress; and 3) analyze the expression of stress-responsive genes under cold stress and a combination of cold and depth stress. Seeds were germinated at 25°C at 1.5- and 10-cm sowing depth for 10d. Seedlings were then exposed to cold stress at 10°C for 6, 24 and 96h, and the expression of cold-, anoxia-, and submergence-inducible genes was analyzed. Control plants were seeded at 1.5cm depth and kept at 25°C. The analysis revealed that cold stress signaling in indica genotypes is more complex than that of japonica as it operates via both the CBF-dependent and CBF-independent pathways, implicated through induction of transcription factors including OsNAC2, OsMYB46 and OsF-BOX28. When plants were exposed to cold + sowing depth stress, a complex signaling network was induced that involved cross talk between stresses mediated by CBF-dependent and CBF-independent pathways to circumvent the detrimental effects of stresses. The experiments revealed the importance of the CBF regulon for tolerance to both stresses in japonica and indica ssp. The mechanisms for cold tolerance differed among weedy indica genotypes and also between weedy indica and cultivated japonica ssp. as indicated by the up/downregulation of various stress-responsive pathways identified from gene expression analysis. The cold-stress response is described in relation to the stress signaling pathways, showing complex adaptive mechanisms in different genotypes.
Assuntos
Resposta ao Choque Frio/genética , Regulação da Expressão Gênica de Plantas , Genes de Plantas/genética , Oryza/crescimento & desenvolvimento , Álcool Desidrogenase/metabolismo , Temperatura Baixa , Proteínas F-Box/genética , Proteínas F-Box/metabolismo , Perfilação da Expressão Gênica , Germinação/genética , Glutamato Desidrogenase/biossíntese , Glutamato Desidrogenase/metabolismo , Oryza/classificação , Oryza/genética , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , alfa-Amilases/metabolismoRESUMO
Low temperature or cold stress and deep sowing plays a pivotal role in limiting rice (Oryza sativa L.) productivity in the temperate rice growing regions as well as in tropical high lands worldwide. A better understanding of stress tolerance mechanism in rice plants will help to develop rice germplasm with improved field level tolerance under variable temperature and sowing deep conditions. Using previously developed stress indices, this study presents results from low temperature and deep sowing screening of four rice genotypes. A group of 25 seeds per replicate (total of 3 replicates) was subjected to stress by deep sowing (15 cm) while another group was subjected to cold stress (13 degrees C-10 h/18 degrees C-14 h) and the control group remained under optimum conditions (25 degrees C and sowing depth of 1.5 cm). The Geometric Mean (GM), Stress Tolerance Index (STI) and Stress Susceptibility Index (SSI) were used to evaluate the genotypic performance under control and stress conditions. The results indicate that it was possible to identify superior genotypes for tolerance based on their stress indices. The indices although correlated, were found to be effective for the selection of genotypes with good yield potential under control and stress treatments and can now be used for genotypic screening under field conditions.