Suarez Rodriguez, Maria Cristina , Adams-Phillips, Lori , Liu, Yidong , Wang, Huachun , Su, Shih-Heng , Jester, Peter , Zhang, Shuqun , Bent, Andrew , Krysan, Patrick J. .
MEKK1 kinase impaired mutant suggests a scaffolding function that is required for MPK4 activation in Arabidopsis.
The Arabidopsis gene MEKK1 encodes a MAPKK Kinase that has been implicated in biotic and abiotic stress response pathways. In the present study, plants homozygous for either of two T-DNA alleles of MEKK1 displayed a severe dwarf phenotype. However, to facilitate our studies we found that the mekk1 dwarf phenotype can be rescued by growth in conditions of elevated temperature or moderate salt stress. Genome-wide expression analysis indicated that mekk1 plants constitutively express Salicylic Acid (SA) related defense response genes. A wild type response to the flagellin elicitor peptide flg22 includes activation of MAP Kinases MPK3, MPK6 and MPK4. mekk1 seedlings treated with flg22 showed activation of MPK3 and MPK6 and lack of activation of MPK4 by in gel kinase assays. Similarly to the mpk4 mutant, mekk1 is rescued by transformation with the salicylate hydroxylase nahG gene. More over, a phenotypic rescue was also attained by the introduction of a kinase-impaired allele of MEKK1 (K361M) into mekk1 knockout plants. Unexpectedly, these K361M plants displayed a wild-type response when treated with flg22 or a variety of abiotic stresses. However, when treated with an avirulent strain of Pseudomonas syringae the K361M plants showed a delayed hypersensitive response. Our results indicate that MEKK1 protein acts as a negative regulator of SA related defense response pathways in Arabidopsis, possibly scaffolding a pathway with MPK4 because this functionality does not require the proteinís kinase activity. Although the kinase activity of MEKK1 appears to be largely dispensable for some pathways in which it was previously implicated, our data suggest that MEKK1 kinase activity may be involved in plant hypersensitive response to P. syringae treatment.
Log in to add this item to your schedule
1 - University of Wisconsin-Madison, Department of Horticulture
2 - University of Wisconsin-Madison, Department of Plant Pathology
3 - University of Missouri-Columbia, Department of Biochemistry
4 - University of Missouri-Columbia, Department of Biochemstry
5 - University of Wisconsin-Madison, Department of Horticulture, 1575 Linden Dr., Madison, Wi, 53706, USA
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM