Evolutionary and Functional Roles of LysMs in Fungal Resistance and PGPR-Mediated Drought Tolerance in Barley

Lysin motif (LysM) receptors perceive microbial glycans to mediate immunity and mutualism in plants. However, the regulatory mechanisms and functional divergence of LysM family members in barley under biotic and abiotic environmental cues remain largely elusive. Here, we systematically characterized the 15-member HvLysM family in barley (Hordeum vulgare). Synteny and evolutionary analyses indicated that the family expanded predominantly via segmental duplications and evolved under strong purifying selection. Transcriptomic profiling of spikes and leaves under fungal infections revealed that HvLysM3, HvLysM10, and HvLysM13 were broadly induced by both Fusarium graminearum and Bipolaris sorokiniana, whereas HvLysM7 and HvLysM8 displayed pathogen-specific divergence. Under drought stress and inoculation with novel plant-growth-promoting rhizobacteria (PGPR) strains (Aeromonas media and Leclercia aquatilis), HvLysM genes exhibited distinct organ- and genotype-dependent expression. Specifically, HvLysM3 was induced in the roots of both tolerant (XZ141) and sensitive (XZ147) genotypes under drought stress combined with PGPR treatment, HvLysM9–HvLysM12 showed contrasting root responses between two barley genotypes, and HvLysM7/HvLysM8 were co-activated by combined drought and PGPR in XZ141 roots. RT-qPCR experiments validated the strain-specific remodeling of HvLysMs transcription. Furthermore, subcellular localization assays demonstrated the plasma membrane targeting of HvLysM2 and HvLysM3 and the extracellular localization of HvLysM8. Collectively, this study identifies that HvLysM3 is a promising candidate gene for future functional validation, providing important genetic targets for enhancing barley resilience.