Understanding Heat Tolerance Mechanism in Groundnut (Arachis hypogaea L.)

Heat stress is a critical constraint to groundnut productivity, causing significant yield losses. In order to dissect the genetic mechanism of heat tolerance in groundnut, a mapping population (JL 24 × 55-437) was developed at ICRISAT. A genetic map was constructed using genotyping by-sequencing, comprising 478 SNP loci spanning 1,961.39 cM. Quantitative trait locus (QTL) analysis identified 45 major QTLs for 21 traits, with three QTL clusters (Cluster-1-Ah03, Cluster-2-Ah12, Cluster-3-Ah20) harbouring 66.6% of these QTLs. These clusters explained phenotypic variance ranging from 10.4% to 49.5%. Candidate genes in these clusters included arahy.J0Y6Y5 (DHHC-type zinc finger family protein), arahy.8ZMT0C (peptide transporter 1), and arahy.92ZGJC (post-illumination chlorophyll fluorescence increase), indicating roles in stress response and signal transduction. To further explore heat tolerance, bulked segregant RNA sequencing (BSR-seq) was performed using 11 heat-tolerant (HT) and 10 heat-sensitive (HS) genotypes derived from the mapping population. Plants were subjected to heat stress (45°C) in a controlled environment, and DEGs were identified in flower (155 DEGs: 84 upregulated, 71 downregulated) and pod tissues (1,097 DEGs: 726 upregulated, 371 downregulated). Gene ontology analysis revealed functional enrichment of iron ion binding proteins in flowers and hydrolase activity genes in pods. In silico analysis of significant DEGs highlighted Phosphatidate cytidyltransferase (PCT) as a key candidate gene, showing an exceptionally high fold change (815.11) between tolerant and sensitive genotypes. PCT plays a potential role in signal transduction and stress response mechanisms. In leaves, HSP17 expression increased many fold increased in tolerant genotypes as compared to sensitive genotypes. Understanding heat tolerance mechanism is the key to developing heat tolerant groundnut cultivars that can thrive well in harsh environments.