Wheat production faces challenges from the need to increase grain yield amid climate change. Additionally, a bottleneck has arisen due to the trade-off between grain weight (GW) and grain number (GN). The GW of wheat has been enhanced through both the ectopic expression of the TaExpA6 gene and a triple mutation in the TaGW2 gene. However, their impact on grain yield and quality traits under elevated temperatures remains largely unknown.

The aim of this study was to evaluate the response of lines carrying these genetic modifications to wheat traits under heat stress. A field experiment was conducted with four genotypes: a transgenic line expressing TaExpA6 in grains, its wild type (WT), a triple mutant of the TaGW2 gene, and its WT, across two thermal treatments: a control at ambient temperature and an increased temperature treatment (+4°C) from booting to 7 days post-anthesis.

The treatments were arranged in a split-plot block design with four replicates, assigning thermal treatments to main plots and genotypes to subplots. The experiment took place in field plots under optimal management, except for the increased temperature treatment. This temperature rise was achieved using polyethylene chambers equipped with heaters and automatic temperature controllers. Data were analysed using ANOVA. GW was enhanced (P< 0.05) in both transformed lines compared to their WTs in control conditions (TaExpA6: 10%; TaGW2: 24%) and under elevated temperatures (TaExpA6: 7%; TaGW2: 22%).

The response of GW in control and heated treatments was consistent across different grain positions within the spike. Treatment effects on GW were corroborated by tracking the time-course of individual grain weight and gene expression dynamics. As expected, the transgenic line showed no significant trade-off with GN (P>0.05), whereas the TaGW2 line did (P<0.05). Elevated temperatures adversely affected GN (6-8%) across all genotypes.

Interestingly, the negative impacts of heating on grain yield and GN observed in the WTs were mitigated in the transformed lines under the same thermal increase, demonstrating partial resilience in grain yield. This resilience was also observed in quality traits, such as the protein concentration in grains.