Induced expression of pathogenesis-related protein genes in soybean by wounding and the Phytophthora sojae cell wall glucan elicitor

Abstract

The effects of the glucan elicitor (WGE) from the cell wall of Phytophthora sojae on the transcriptional upregulation of genes representing five families of pathogenesis-related (PR) proteins have been investigated in soybean under wound and minimal-wound conditions. Although each has its own expression pattern, these PR protein genes can be broadly categorized into two groups. Induced expression of genes for PR-1a and PR-10 is predominantly limited to cells proximal to the point of treatment, while that of genes for the elicitor-releasing endo-glucanase (GLU, a PR-2), a WIN-like protein (WIN, a PR-4) and a Kunitz trypsin inhibitor (KTI, a PR-6) is seen in proximal, near-proximal and distal cells. GLU is the only family that shows weak though detectable constitutive (basal) gene expression. Wounding induces only barely detectable to weak expression of genes for PR-1a and KTI and somewhat stronger expression of those for GLU, WIN and PR-10. PR-1a gene expression is essentially induced only by WGE; similarly, that for KTI is greatly enhanced by WGE. While gene expression for PR-10 is induced by wounding, it is also strongly upregulated by WGE in a minimal wound background, suggesting a possibly independent effect of WGE. Finally, WGE also enhances the speed and magnitude of expression of GLU and WIN genes in all cell zones. Methyl jasmonate induces strong gene expression for KTI and the ethylene precursor, ACC, and jasmonic acid (JA) enhance that of GLU. The results are discussed in the context of the recently observed WGE- and JA-induced distal defense potentiation in soybean.