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DEVELOPMENT AND HORMONE ACTION

An Arabidopsis Mitogen-Activated Protein Kinase Cascade, MKK9-MPK6, Plays a Role in Leaf Senescence^{1,[C],[W],[OA]}

Department of Horticulture, Cornell University, Ithaca, New York 14853

Leaf senescence is a developmentally programmed cell death process that constitutes the final step of leaf development, and it can be regulated by multiple environmental cues and endogenous signals. The mitogen-activated protein kinase (MAPK) cascades play diverse roles in intracellular and extracellular signaling in plants. Roles of the MAPK signaling module in leaf senescence are unknown. Here, a MAPK cascade involving MKK9-MPK6 is shown to play an important role in regulating leaf senescence in Arabidopsis (Arabidopsis thaliana). Both MKK9 and MPK6 possess kinase activities, with MPK6 an immediate target of MKK9, as revealed by in vitro, in vivo, and in planta assays. The constitutive and inducible overexpression of MKK9 causes premature senescence in leaves and in whole Arabidopsis plants. The premature senescence phenotype is suppressed when MKK9 is overexpressed in the mpk6 null background. When either MKK9 or MPK6 is knocked out, leaf senescence is delayed.

² Present address: Department of Microbiology, Immunology, and Molecular Genetics, University of Kentucky College of Medicine, Lexington, KY 40536.

³ Present address: Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Susheng Gan (sg288{at}cornell.edu).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.108.133439

^* Corresponding author; e-mail sg288{at}cornell.edu.

Received November 29, 2008; accepted February 24, 2009; published February 27, 2009.

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