Specific domain structures control ABA, SA, and stress mediated SIZ1 phenotype

Mi Sun Cheong, Purdue University

Abstract

SIZ1 encodes the ortholog of mammalian PIAS and yeast SIZ SUMO E3 ligases in Arabidopsis (Arabidopsis thaliana ). As other PIAS proteins, four conserved motifs in SIZ1 include SAP (Scaffold attachment factor A/B//acinus/ PIAS domain), PINIT, SP-RING (SIZ/ PIAS-RING) and SXS motifs. SIZ1 contains, in addition, a PHD ( Plant Homeodomain) typical of plant PIAS proteins. To understand function of each structural domain for SIZ1 functions, conserved amino acids were changed in each structural domain based on domain studies in animal and yeast. Since mutated proteins were stably expressed in plant cells and interacted with SUMO1, I determined phenotypes of siz1-2 knockout mutants transformed with SIZ1 alleles carrying point mutations in the domains. Domain SP-RING is required for SUMO conjugation activity of SIZ1. SA accumulation and SA-dependent phenotypes of siz1-2, such as diminished plant size, heightened innate immunity and ABA inhibition of cotyledon greening, as well as SA-independent basal thermo-sensitivity 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 ABA. 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.

Degree

Ph.D.

Advisors

Bressan, Purdue University.

Subject Area

Molecular biology

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