Mapping stress memory: genetic and epigenetic insights into combined drought and heat tolerance in barley.

Unveiling genetic and epigenetic mechanisms in barley, this study maps stress memory under combined drought and heat, advancing resilience breeding for climate-adaptive crop improvement. Barley is one of the world's most important cereal crops and is increasingly threatened by concurrent drought and heat stress, two major environmental factors intensified by climate change. In our study, we employed a genome-wide association scan (GWAS) to investigate the concept of "stress memory," wherein barley plants exposed to previous stress events exhibit enhanced responses to subsequent ones. We evaluated key agronomic traits, such as plant height, spike length, grain number, and thousand kernel weight along with biochemical markers such as chlorophyll content, proline, and soluble proteins across three generations under combined drought and heat stress. This approach encompassed transgenerational and intergenerational stress memory and a third generation that could reveal the potential cumulative effects of combined drought and heat stress. Our findings demonstrated a significant increase in metabolites specifically proline and soluble proteins in third-generation barley plants compared to those exposed to stress for only one or two generations. Through GWAS analysis, we identified 332 highly significant SNP markers clustered within 14 genomic regions on chromosomes 2H, 3H, 4H, 5H, and 7H. These regions are associated with all evaluated physiological and morphological traits under stress that harbor several potential candidate genes implicated in regulating complex signaling pathways, reactive oxygen species scavenging, and energy metabolism processes essential for mitigating the impacts of drought and heat. These results underscore the intricate nature of barley's stress tolerance mechanisms and highlight the potential for integrating genomics, epigenomics, and advanced phenotyping approaches into breeding programs.