title: The Arabidopsis MAP kinase kinase 7: A crosstalk point between auxin signaling and defense responses?
abstract: Plant-pathogen interaction induces a complex host response that coordinates various signaling pathways through multiple signal molecules. Besides the well-documented signal molecules salicylic acid (SA), ethylene and jasmonic acid, auxin is emerging as an important player in this response. We recently characterized an Arabidopsis activation-tagged mutant, bud1, in which the expression of the MAP kinase kinase 7 (AtMKK7) gene is increased. The bud1 mutant plants accumulate elevated levels of SA and display constitutive pathogenesis-related (PR) gene expression and enhanced resistance to pathogens. Additionally, increased expression of AtMKK7 in the bud1 mutant causes deficiency in polar auxin transport, indicating that AtMKK7 negatively regulates auxin signaling. Based on these results, we hypothesized that AtMKK7 may serve as a crosstalk point between auxin signaling and defense responses. Here we show that increased expression of AtMKK7 in bud1 results in a significant reduction in free auxin (indole-3-acetic acid) levels in the mutant plants. We propose three possible mechanisms to explain how AtMKK7 coordinates the growth hormone auxin and the defense signal molecule SA in the bud1 mutant plants. We suggest that AtMKK7 may play a role in cell death and propose that AtMPK3 and AtMPK6 may function downstream of AtMKK7.
authors.affiliation: Department of Microbiology and Cell Science; University of Florida; Gainesville, Florida USA.
authors.forename: Xudong
authors.initials: X
authors.lastname: Zhang
authors.forename: Yuqing
authors.initials: Y
authors.lastname: Xiong
authors.forename: Christopher
authors.initials: C
authors.lastname: Defraia
authors.forename: Eric
authors.initials: E
authors.lastname: Schmelz
authors.forename: Zhonglin
authors.initials: Z
authors.lastname: Mou
references.citation: Plant Cell. 2002 Sep;14(9):2031-43
references.pmid: 12215503
references.citation: Plant Cell. 1997 May;9(5):809-24
references.pmid: 9165755
references.citation: Plant Cell. 2006 Feb;18(2):308-20
references.pmid: 16377756
references.citation: Proc Natl Acad Sci U S A. 1998 Dec 8;95(25):15107-11
references.pmid: 9844023
references.citation: Trends Plant Sci. 2002 Jul;7(7):301-8
references.pmid: 12119167
references.citation: Plant Cell. 1996 Dec;8(12):2309-23
references.pmid: 8989885
references.citation: Science. 1995 Dec 22;270(5244):1988-92
references.pmid: 8533090
references.citation: Plant J. 2007 Dec;52(6):1066-79
references.pmid: 17908155
references.citation: Curr Opin Plant Biol. 2006 Aug;9(4):436-42
references.pmid: 16759898
references.citation: Nature. 1998 Aug 6;394(6693):585-8
references.pmid: 9707120
references.citation: Science. 2006 Apr 21;312(5772):436-9
references.pmid: 16627744
references.citation: Plant Cell. 1996 Oct;8(10):1773-91
references.pmid: 8914325
references.citation: Plant Physiol. 1996 Apr;110(4):1367-1379
references.pmid: 12226267
references.citation: Genes Dev. 2006 Jul 1;20(13):1790-9
references.pmid: 16818609
references.citation: Proc Natl Acad Sci U S A. 1998 Aug 18;95(17):10328-33
references.pmid: 9707647
references.citation: J Biol Chem. 2004 Nov 19;279(47):49229-35
references.pmid: 15371431
references.citation: Appl Environ Microbiol. 1987 Aug;53(8):1839-45
references.pmid: 16347409
references.citation: Proc Natl Acad Sci U S A. 1986 Sep;83(18):6935-9
references.pmid: 16593762
references.citation: Plant Physiol. 1996 Apr;110(4):1381-1394
references.pmid: 12226268
references.citation: Plant Cell. 1996 Oct;8(10):1793-1807
references.pmid: 12239362
references.citation: Plant J. 2007 Mar;49(6):1030-40
references.pmid: 17319846
references.citation: Plant J. 2003 Jan;33(2):245-57
references.pmid: 12535339
references.citation: Proc Natl Acad Sci U S A. 1982 May;79(9):2812-6
references.pmid: 16593184
references.citation: Annu Rev Plant Physiol Plant Mol Biol. 1997 Jun;48:251-275
references.pmid: 15012264