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The grain‐filling stage in Triticum aestivum (wheat) is highly vulnerable to increasing temperature as terminal heat stress diminishes grain quality and yield. To examine the mechanism of terminal heat tolerance, we performed the biochemical and gene expression analyses using two heat‐tolerant (WH730 and WH1218) and two heat‐sensitive (WH711 and WH157) wheat genotypes. We observed a significant increase in total soluble sugar (25%–47%), proline (7%–15%), and glycine betaine (GB) (22%–34%) contents in flag leaf, whereas a decrease in grain‐filling duration, 1000‐kernel weight (8%–25%), and grain yield per plant (11%–23%) was observed under the late‐sown compared to the timely sown. The maximum content of osmolytes, including total soluble sugar, proline, and GB, was observed in heat‐tolerant genotypes compared to heat‐sensitive genotypes. The expression of 10 heat‐responsive genes associated with heat shock proteins (sHsp‐1, Hsp17, and HsfA4), flavonoid biosynthesis (F3′‐1 and PAL), β‐glucan synthesis (CslF6 and CslH), and xyloglucan metabolism (XTH1, XTH2, and XTH5) was studied in flag leaf exposed to different heat treatments (34, 36, 38, and 40°C) at 15 days after anthesis by quantitative real‐time polymerase chain reaction. A significant increase in the relative fold expression of these genes with increasing temperature indicated their involvement in providing heat‐stress tolerance. The high differential expression of most of the genes in heat‐tolerant genotype “WH730” followed by “WH1218” indicates the high adaptability of these genotypes to heat stress compared to heat‐sensitive wheat genotypes. Based on the previous results, “WH730” performed better in terms of maximum osmolyte accumulation, grain yield, and gene expression under heat stress.

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Grain yield is one of the most important aims for combating the needs of the growing world population. The role of development and nutrient transfer in flag leaf for higher yields at the grain level is well known. It is a great challenge to properly exploit this knowledge because all the processes, starting from the emergence of the flag leaf to the grain filling stages of wheat (Triticum aestivum L.), are very complex biochemical and physiological processes to address. This study was conducted with the primary goal of functionally and structurally annotating the candidate genes associated with different developmental stages of flag leaf in a comprehensive manner using a plethora of in silico tools. Flag leaf-associated genes were analyzed for their structural and functional impacts using a set of bioinformatics tools and algorithms. The results revealed the association of 17 candidate genes with different stages of flag leaf development in wheat crop. Of these 17 candidate genes, the expression analysis results revealed the upregulation of genes such as TaSRT1-5D, TaPNH1-7B, and TaNfl1-2B and the downregulation of genes such as TaNAP1-7B, TaNOL-4D, and TaOsl2-2B can be utilized for the generation of high-yielding wheat varieties. Through MD simulation and other in silico analyses, all these proteins were found to be stable. Based on the outcome of bioinformatics and molecular analysis, the identified candidate genes were found to play principal roles in the flag leaf development process and can be utilized for higher-yield wheat production.