Disease Resistance and Abiotic Stress Tolerance in Rice Are Inversely Modulated by an Abscisic Acid–Inducible Mitogen-Activated Protein Kinase[W]

TLDR

Mitogen‑activated protein kinase cascades mediate stress responses in eukaryotes, yet their role in coordinating biotic and abiotic defense pathways remains largely unknown. The authors generated rice lines overexpressing or silencing OsMAPK5 via a CaMV 35S promoter or dsRNAi to assess its biological function. OsMAPK5 overexpression enhanced drought, salt, and cold tolerance, whereas its suppression induced constitutive PR gene expression and increased disease resistance but compromised abiotic stress tolerance, indicating that OsMAPK5 positively regulates abiotic stress tolerance while negatively modulating disease resistance.

Abstract

Abstract Mitogen-activated protein kinase (MAPK) cascades play an important role in mediating stress responses in eukaryotic organisms. However, little is known about the role of MAPKs in modulating the interaction of defense pathways activated by biotic and abiotic factors. In this study, we have isolated and functionally characterized a stress-responsive MAPK gene (OsMAPK5) from rice. OsMAPK5 is a single-copy gene but can generate at least two differentially spliced transcripts. The OsMAPK5 gene, its protein, and kinase activity were inducible by abscisic acid as well as various biotic (pathogen infection) and abiotic (wounding, drought, salt, and cold) stresses. To determine its biological function, we generated and analyzed transgenic rice plants with overexpression (using the 35S promoter of Cauliflower mosaic virus) or suppression (using double-stranded RNA interference [dsRNAi]) of OsMAPK5. Interestingly, suppression of OsMAPK5 expression and its kinase activity resulted in the constitutive expression of pathogenesis-related (PR) genes such as PR1 and PR10 in the dsRNAi transgenic plants and significantly enhanced resistance to fungal (Magnaporthe grisea) and bacterial (Burkholderia glumae) pathogens. However, these same dsRNAi lines had significant reductions in drought, salt, and cold tolerance. By contrast, overexpression lines exhibited increased OsMAPK5 kinase activity and increased tolerance to drought, salt, and cold stresses. These results strongly suggest that OsMAPK5 can positively regulate drought, salt, and cold tolerance and negatively modulate PR gene expression and broad-spectrum disease resistance.