Genetics of Heat Tolerance in the Bengal and Assam Aus Panel of Rice

Abstract

Rice (Oryza sativa L.) is considered as the main stable food and largest grain crop in many Asian countries since they rely on it for basic nutrition. During the past few years, the temperature in rice-growing regions has been rising, and extreme high temperature events are increasingly frequent, potentially causing crop damage. Heat stress caused by rising temperature over the optimal range is a significant abiotic stress affecting rice production. Heat stress can negatively affect plant growth, development and productivity, causing a loss of yield. Therefore, developing heat tolerant rice varieties is essential. In this work, heat tolerance was evaluated in 204 rice cultivars, mostly from Bengal and Assam Aus Panel (BAAP). High heat tolerant genotypes were identified using two approaches: spikelet fertility and chlorophyll fluorescence. For spikelet fertility, the heat tolerant genotypes identified were ARC 14965, ARC 10392 and Goria. For chlorophyll fluorescence, the genotypes identified were KALI AUS, Code No BI 93 and AUS 130. Genome-wide association (GWA) mapping was conducted on the heat tolerance trait with two million SNPs using an efficient mixed model (EMMA). The total number of QTLs associated with traits related to heat tolerance identified were 23 in fertility trait and 10 QTLs in photosynthetic trait. A number of these QTLs contained functional candidate genes. A total of seven candidate genes were identified for control/treatment ratio; SEC14, Hsp20, AP2/ERF, WRKY28, miRNA156, OsDjC56 and ZOS6-06 and three for QY trait after 60 minutes; PHD13, OsSTA65 and CGN. Additionally, RNA-sequencing analysis (RNA-seq) was conducted on spikelet fertility trait and well-known heat tolerant genes were detected such as (OsMYB55, OsHTASb and OsHSFC1b). Through the combination of GWA and transcriptomic analysis two excellent candidate genes associated with heat tolerance in rice were identified, namely; miRNA156 and OsDjC56. In addition, the candidate gene CGN in the leave study differentially expressed in the RNA-seq. In conclusion, the heat tolerant genotypes and QTLs and candidate genes identified in this study could be serve as valuable resource for further advanced research in rice heat tolerance and for breeding programs aimed at enhancing sustainable rice production. Such work could make an important contribution in supporting global food security worldwide.