Minisymposium 1: Mineral nutrition

Abs # 11002: AtSIZ1 is a SUMO E3 ligase that controls plant phosphate deficiency responses and development of Arabidopsis

Presenter:	Miura, Kenji , mkenji@purdue.edu
Authors	Miura, Kenji  (A)   Rus, Ana  (A)   Sharkhuu, Altanbadralt  (A)   Lee, Byeong-ha  (B)   Yokoi, Shuji  (A)   Karthikeyan, Athikkattuvalasu S (C)   Raghothama, Kashchandra G (C)   Baek, Dongwon  (D)   Koo, Yoon Duck  (D)   Yun, Dae-Jin  (D)   Bressan, Ray A (A)   Hasegawa, Paul M (A)
Affiliations:	(A): Center for Plant Environmental Stress Physiology, Purdue University (B): Department of Plant Sciences, University of Arizona (C): Department of Horticulture and Landscape Architecture, Purdue University (D): Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University

Covalent attachment of peptide moieties to proteins is a post-translational regulatory process that leads to modulation of protein stability, activity, and localization. Sumoylation, a process conserved across plant, animal and fungal kingdoms, cojugates the small ubiquitin-related modifier (SUMO) peptide to proteins and is considered to be a major control point in hormone and stress signaling acting through the modulation of transcriptional activators. We report the identification and functional analysis of AtSIZ1 as a SUMO E3 ligase that is involved in plant responses to phosphate (Pi) deficiency. Dysfunctional T-DNA insertional alleles (siz1-1, siz1-2, and siz1-3) of AtSIZ1 (At5g60410) cause Arabidopsis thaliana plants to exhibit hypersensitivity to Pi deficiency. siz1-1, 1-2, and 1-3 seedlings exhibit Pi starvation phenotypes that are more substantial than wild type, including cessation of primary root growth, extensive lateral root development, and shoot anthocyanin accumulation even though Pi_int levels are comparable in seedlings of all genotypes. Sequence analysis identified the AtSIZ1 gene product as a potential ortholog of Siz1/PIAS SUMO E3 ligases. Pi-starvation responsive genes, including AtPT2 (encoding a high affinity Pi transporter), AtPS2 (acid phosphatase), and AtPS3 (glycerol phosphate permease), but neither AtIPS1 nor RNS1 (ribonuclease), are expressed in siz1 mutant plants that are grown even under Pi sufficient conditions. All of these genes are induced in siz1 plants to the same extent as in wild type by Pi starvation. Analysis of AtSIZ1:GFP expression indicated that AtSIZ1 is localized to subnuclear compartments. Recombinant AtSIZ1 facilitates in vitro sumoylation of the yeast Cdc3 protein when combined with yeast SUMO, E1 and E2 proteins. Western blot analysis of total proteins revealed that the siz1 plants contain less SUMO-conjugates and more free AtSUMO1 than wild type plants. Soil or hydroponic grown plants are reduced in size, although this phenotype is not linked to altered Pi responses. Together, these results suggest that AtSIZ1 functions as a plant SUMO E3 ligase, that regulates Pi signaling and utilization. AtSIZ1 may enable plants to coordinate Pi sensitivity and plant growth and development signaling through sumoylation.