Characteristics of the MAPK gene family in Zizania latifolia and MAPK3 role in response to fungal pathogen infection.

The stems of Zizania latifolia, an important vegetable in China, are targeted by the pathogen Ustilago esculenta, triggering a response through the mitogen-activated protein kinase (MAPK) signalling pathway. To investigate the characteristics and the role of MAPK gene family in the biological stress response, a bioinformatics-based analysis was performed, and the expression patterns of ZlMPKs and MAPK-infection pathway-related genes were detected in male plants inoculated with U. esculenta. Twenty-five ZlMPK genes were identified and divided into four subgroups A, B, C and D: carried a conserved TEY motif, while D had a conserved TDY motif. The ZlMPKs were located in the nucleus, cytoplasm, chloroplast, mitochondria, and peroxisome, and most exhibited evidence of gene duplication events. The relative expression of most ZlMPKs was the highest at 3 h after inoculation with U. esculenta, with 21 ZlMPKs being upregulated and four being downregulated. Additionally, nine of 11 MAPK-infection pathway-related genes were upregulated at 3 h after inoculation. ZlMPK3 was cloned and transformed into Arabidopsis thaliana, and two overexpression lines were identified by resistance screening and molecular detection. Their responses to Botrytis cinerea infection were studied. The leaf inoculation sites of ZlMPK3-overexpression plants revealed damage, while those of wild-type plants did not. The relative expression of MAPK pathogen related genes was altered after inoculation. Specifically, the expression levels of the ethylene biosynthetic pathway gene AtACS6 and five cysteine-rich secretory protein CAP genes were significantly upregulated, while those of systemic acquired resistance marker gene, pathogenesis-related 1 AtPR1 and early defense signalling gene AtFRK1 were significantly downregulated, indicating that resistance to B. cinerea was weakened in the ZlMPK3-overexpression lines.