A fungal-responsive MAPK cascade regulates phytoalexin biosynthesis in Arabidopsis

doi:10.1073/pnas.0711301105

A fungal-responsive MAPK cascade regulates phytoalexin biosynthesis in Arabidopsis

*State Key Laboratory of Plant Physiology and Biochemistry, China Agricultural University, Beijing 100094, China;
^†Department of Biochemistry, University of Missouri, Columbia, MO 65211; and
^§Department of Plant Biology and Center for Microbial and Plant Genomics, University of Minnesota, St. Paul, MN 55108

Edited by Roger N. Beachy, Donald Danforth Plant Science Center, St. Louis, MO, and approved February 14, 2008 (received for review November 29, 2007)

Abstract

Plant recognition of pathogens leads to rapid activation of MPK3 and MPK6, two Arabidopsis mitogen-activated protein kinases (MAPKs), and their orthologs in other species. Here, we report that synthesis of camalexin, the major phytoalexin in Arabidopsis, is regulated by the MPK3/MPK6 cascade. Activation of MPK3/MPK6 by expression of active upstream MAPK kinase (MAPKK) or MAPKK kinase (MAPKKK) was sufficient to induce camalexin synthesis in the absence of pathogen attack. Induction of camalexin by Botrytis cinerea was preceded by MPK3/MPK6 activation, and compromised in mpk3 and mpk6 mutants. Genetic analysis placed the MPK3/MPK6 cascade upstream of PHYTOALEXIN DEFICIENT 2 (PAD2) and PAD3, but independent or downstream of PAD1 and PAD4. Camalexin induction after MPK3/MPK6 activation was preceded by rapid and coordinated up-regulation of multiple genes encoding enzymes in the tryptophan (Trp) biosynthetic pathway, in the conversion of Trp to indole-3-acetaldoxime (IAOx, a branch point between primary and secondary metabolism), and in the camalexin biosynthetic pathway downstream of IAOx. These results indicate that the MPK3/MPK6 cascade regulates camalexin synthesis through transcriptional regulation of the biosynthetic genes after pathogen infection.

Footnotes

^¶To whom correspondence should be addressed. E-mail: zhangsh{at}missouri.edu
Author contributions: D.R. and Y.L. contributed equally to this work; S.Z. designed research; D.R., Y.L., K.-Y.Y., L.H., G.M., and J.G. performed research; J.G. contributed new reagents/analytic tools; D.R., Y.L., J.G., and S.Z. analyzed data; and S.Z. wrote the paper.
↵ ^‡Present address: Department of Plant Biotechnology, Chonnam National University, Gwangju 500-757, South Korea.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
This article contains supporting information online at www.pnas.org/cgi/content/full/0711301105/DCSupplemental.