Genome-wide analysis of the barley MAPK gene family and its expression patterns in relation to Puccinia hordei infection

Abstract

Mitogen-activated protein kinases (MAPKs) have been shown to act as key regulators of stress responses in model plant and crop species. So far, however, the MAPK family has not been systematically studied in barley. Herein, we identified 16 HvMAPKs (Hv—Hordeum vulgare) based on computational analysis of barley transcriptomics and genomics databases. HvMAPKs contain all canonical MAPK domains, except for HvMPK2, which lacks a MAPK domain signature. In addition, five HvMAPKs harbor TEY and ten HvMAPKs harbor TDY dual phosphorylation motif in the activation loop. Interestingly, HvMPK2 contains a MEY instead of TEY phosphorylation motif. We classified HvMAPKs into four major plant MAPK clades based on phylogeny reconstruction and anchored all HvMAPK genes to five out of seven barley chromosomes. Furthermore, we inoculated seedlings of susceptible barley line L94 and its isolines L94-Rph3 and L94-Rph7 with rust fungus Pucciniahordei and analyzed the expression of 16 HvMAPK genes using qRT-PCR at 1–4.5 days post inoculation. In total, six HvMAPK genes exhibited significantly altered expression by P. hordei infection. The expression of HvMPK5, HvMPK6, HvMPK7 and HvMPK12 (set one genes) was strongly induced especially during effector-triggered immunity (ETI), whereas the expression of HvMPK2 and HvMPK17 (set two genes) was specifically downregulated during ETI. Yet the expression of HvMPK8 was also specifically but weakly downregulated during ETI. Overall, the expression patterns suggest that set one genes positively regulate ETI in barley–P. hordei pathosystem, whereas set two genes negatively regulate ETI and/or programmed cell death in this pathosystem.