Transcriptional analysis and histochemistry reveal a dominant role for cell wall signaling in mediating Pythium myriotylum resistance in Zingiber zerumbet

Abstract

Abstract Although post infection changes in cell wall constituents are known to induce the immune response in plants against necrotrophs, little is known about the role of the cell wall in mediating resistance in Zingiber zerumbet (L.) Smith (Zingiberaceae) against the soil-borne necrotrophic oomycete Pythium myriotylum Drechsler, which causes soft-rot disease. Using RNA-Seq in combination with custom gene expression microarray we studied the temporal expression profile of 46 wall-associated genes in Z. zerumbet against P. myriotylum inoculation. Many genes that promote cell wall loosening were suppressed. Similarly, the genes involved in the biosynthesis and the signaling of phytohormones and the receptor-like kinases that mediate cell elongation were also suppressed. Several monolignol biosynthetic pathway genes were up-regulated. Histochemistry of the collar region of the aerial stem revealed H2O2 accumulation, increased lignification of the mesophyll cells surrounding vascular bundles in the leaf sheath and the significant increase in total lignin content. Pathogen hyphae were restricted to peripheral leaf sheath and were not extended into the pith through which the principal portion of the connective tissues passes in the aerial stem. Results highlight a coordinated transcriptional reprogramming of cell wall-associated genes to bring about changes in cell wall composition to minimize the cell wall damage caused by pathogen factors and to render the cell wall less amenable to pathogen penetration. The study illustrates a key role for cell wall fortification in preventing pathogen colonization in the vascular tissues, thus ensuring the transport system remains unaffected by the pathogen invasion.