Studies on molecular aspects of high temperature tolerance in Banana

Abstract

Banana is a tropical fruit crop. Screening and identification of cultivars for high temperature newlinestress conditions is necessary due global warming phenomenon. In this regard, a temperature newlineinduction response (TIR) technique, which is based on the principle of subjecting plantlets to newlinesublethal temperatures and subsequent exposure to challenging temperatures, and further newlineassessing growth and recovery was standardised for banana. Based on least survival (4%) and newlinehighest growth reduction (92%) during recovery of plantlets, 55°C for 2 h was identified as newlinechallenging temperature or lethal temperature. The induction temperature, 42°C for 2 h 30 min, newlineat which resulted in more than 50% of the plantlets survival and a lower reduction in growth newline(20%) during recovery after exposure to lethal temperatures (55°C for 2 h) were identified as newlinethe optimum induction temperature. Twenty banana cultivars were screened using TIR newlinetechnique and based on recovery growth and per cent reduction, Z distribution analysis was newlinedone to identify contrasting genotypes. Genotypes grouped into tolerant (cvs. Grand Naine and newlineRasbale), which clustered in quadrant I, and susceptible (cvs. Red Banana and Kunnan), which newlineclustered in quadrant III were identified for further analysis. Membrane Injury index was lower newlinein cv. Grand Naine (tolerant) compared to cv. Red Banana (susceptible). Antioxidant enzyme newlineanalysis showed enhanced levels of Superoxide dismutase (SOD), peroxidase (POX), catalase newline(CAT), glutathione reductase (GR) in Grand Naine when compared to Red Banana under heat newlinestress when seedlings were induced with sub lethal temperature. Similar trend was observed newlinein metabolite analysis where, sugars, proline and glycine betaine were found to be higher in newlinetolerant genotype indicating their role as osmoprotectants. Fatty analysis showed a change in newlinedegree of higher saturation levels in tolerant genotypes newlineTo understand an acquired thermotolerance phenomenon at the molecular level, the newlineRNA-seq analysis was done at induction, induction+lethal and only lethal temperature treated newlineGrand naine seedlings. The number of differentially expressed genes under induction (I) was newline3936, I+L was 2268 and lethal stress was 907 compared to control plants. Gene ontology and newlineDGE analysis showed that genes related to heat shock factors, heat shock proteins, stress newlineassociated proteins, ROS scavenging, fatty acid metabolism, protein modification were newlinesignificantly up regulated during induction, thus preparing the organism or tissue for high newlinetemperature tolerance. Further, we identified and examined the expression of miRNAs and newlinetheir predicted target genes expression levels during heat stress in banana. Out of 235 miRNAs newlinefound in Musa, 40 miRNA showed homology to heat responsive miRNAs from plants. Further, newlinefourteen target genes for miRNA were predicted, and were monitored under three stages of newlinestress viz, induction, induction + lethal and lethal stress alone using qPCR analysis. The results newlinesuggest that there is a general negative relationship in the expression patterns of miRNA and newlinetheir predicted targets, indicating their role in acquired thermo-tolerance., We also identified newlinea total of 363 novel HS-lncRNA and were classified as 288 lincRNAs, 71 antisense LncRNA, newline5 sense lncRNAs. Differential expression of lncRNA showed varied patterns at different stages newlineinduction and lethal stress. The Cytoscape analysis showed that genes involved in protein newlinecoding, membrane integrity and signal transduction pathways were altered during thermostolerance newline. The findings this study helps in understanding the role of induction stress in higher newlineheat stress tolerance at biochemical and molecular level. newline