Poster: Regulation of gene expression

Abs # 790: AtSIZ1 is a SUMO E3 ligase that controls phosphate utilization

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

A T-DNA insertion mutation (siz1-1) in the AtSIZ1 locus (At5g60410) of Arabidopsis thaliana seedlings was identified based on a hypersensitive phosphate (Pi) starvation response. Subsequently, two other independent alleles, siz1-2 and siz1-3, were obtained from the SIGnAL sequence-indexed insertion population. The siz1-1, 1-2, and 1-3 exhibited similar phenotypes when grown on Pi deficient media; decreased primary and increased lateral root elongation relative to wild type seedlings. This Pi starvation response of seedlings occurred despite Pi_int accumulation that is similar to wild type plants. Several Pi-starvation responsive genes, including AtPT2 (encoding a high affinity Pi transporter) and AtPS2 (acid phosphatase), were expressed even when the siz1 mutants were grown under Pi sufficient conditions. Phylogenic analysis revealed that AtSIZ1 is sequence similar to Siz1/PIAS, which are necessary for the ligation step (E3) in the sumoylation conjugation system. Analysis of AtSIZ1:GFP expression indicated that AtSIZ1 is localized in nuclear speckles. AtSIZ1 facilitates in vitro sumoylation of the yeast Cdc3 when combined with yeast SUMO E1 and E2 proteins. Western blot analysis of total proteins revealed that the siz1 mutants contain less SUMO-conjugates and more free AtSUMO1 than wild type plants. Together, these results suggest that AtSIZ1 functions as a plant SUMO E3 ligase, which regulates Pi signaling and utilization.