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ENVIRONMENTAL STRESS AND ADAPTATION TO STRESS

Specific Domain Structures Control Abscisic Acid-, Salicylic Acid-, and Stress-Mediated SIZ1 Phenotypes^1,[W]

Division of Applied Life Science (Brain Korea 21 Program), PMBBRC, EB-NCRC, Gyeongsang National University, Jinju City 660–701, Korea (M.S.C., H.C.P., M.J.H., J.L., W.C., H.J.B., S.Y.L., D.-J.Y.); Department of Horticulture and Landscape Architecture, Purdue University, West Lafayette, Indiana 47907 (M.S.C., R.A.B.); Research Center for Molecular and Developmental Biology, Key Laboratory of Photosynthesis and Environmental Molecular Physiology, Institute of Botany, Chinese Academy of Science, Beijing 100093, China (J.B.J.); and Department of Plant Biology and Department of Crop Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801 (H.J.B.)

SIZ1 (for yeast SAP and MIZ1) encodes the sole ortholog of mammalian PIAS (for protein inhibitor of activated STAT) and yeast SIZ SUMO (for small ubiquitin-related modifier) E3 ligases in Arabidopsis (Arabidopsis thaliana). Four conserved motifs in SIZ1 include SAP (for scaffold attachment factor A/B/acinus/PIAS domain), PINIT (for proline-isoleucine-asparagine-isoleucine-threonine), SP-RING (for SIZ/PIAS-RING), and SXS (for serine-X-serine, where X is any amino acid) motifs. SIZ1 contains, in addition, a PHD (for plant homeodomain) typical of plant PIAS proteins. We determined phenotypes of siz1-2 knockout mutants transformed with SIZ1 alleles carrying point mutations in the predicted domains. Domain SP-RING is required for SUMO conjugation activity and nuclear localization of SIZ1. Salicylic acid (SA) accumulation and SA-dependent phenotypes of siz1-2, such as diminished plant size, heightened innate immunity, and abscisic acid inhibition of cotyledon greening, as well as SA-independent basal thermotolerance were not complemented by the altered SP-RING allele of SIZ1. The SXS domain also controlled SA accumulation and was involved in greening and expansion of cotyledons of seedlings germinated in the presence of abscisic acid. Mutations of the PHD zinc finger domain and the PINIT motif affected in vivo SUMOylation. Expression of the PHD and/or PINIT domain mutant alleles of SIZ1 in siz1-2 promoted hypocotyl elongation in response to sugar and light. The various domains of SIZ1 make unique contributions to the plant's ability to cope with its environment.

² Present address: Department of Molecular Genetics and Cell Biology, The University of Chicago, 1103 E. 57th St. EBC410, Chicago, IL 60637.

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: Dae-Jin Yun (djyun{at}gnu.ac.kr).

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

www.plantphysiol.org/cgi/doi/10.1104/pp.109.143719

^* Corresponding author; e-mail djyun{at}gnu.ac.kr.

Received June 26, 2009; accepted October 10, 2009; published October 16, 2009.

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