- Sumoylation is a post-translational regulatory process in diverse cellular processes in eukaryotes, involving conjugation/deconjugation of small ubiquitin-like modifier (SUMO) proteins to other proteins thus modifying their function. The PIAS [protein inhibitor of activated signal transducers and activators of transcription (STAT)] and SAP (scaffold attachment factor A/B/acinus/PIAS)/MIZ (SIZ) proteins exhibit SUMO E3-ligase activity that facilitates the conjugation of SUMO proteins to target substrates. Here, we report the isolation and molecular characterization of Oryza sativa SIZ1 (OsSIZ1) and SIZ2 (OsSIZ2), rice homologs of Arabidopsis SIZ1. The rice SIZ proteins are localized to the nucleus and showed sumoylation activities in a tobacco system. Our analysis showed increased amounts of SUMO conjugates associated with environmental stresses such as high and low temperature, NaCl and abscisic acid (ABA) in rice plants. The expression of OsSIZ1 and OsSIZ2 in siz1-2 Arabidopsis plants partially complemented the morphological mutant phenotype and enhanced levels of SUMO conjugates under heat shock conditions. In addition, ABA-hypersensitivity of siz1-2 seed germination was partially suppressed by OsSIZ1 and OsSIZ2. The results suggest that rice SIZ1 and SIZ2 are able to functionally complement Arabidopsis SIZ1 in the SUMO conjugation pathway. Their effects on the Arabidopsis mutant suggest a function for these genes related to stress responses and stress adaptation .
- OsSIZ1 Regulates the Vegetative Growth and Reproductive Development in Rice.Two homologous genes from rice (Oryza sativa) were isolated and designated as OsSIZ1 and OsSIZ2 based on amino acid sequence homology to AtSIZ1 and their phylogenetic relationship. The function in the vegetative growth and reproductive development in rice was investigated using OsSIZ1 mutants containing a T-DNA insertion. The results showed that the mutant Ossiz1 exhibited the significant changes in several growth and developmental parameters, including primary root length, adventitious root number, plant height, leaf and panicle length, flower formation, and seed-setting rate compared with wild type. Taking together these results indicate that OsSIZ1 plays an important role in regulating growth and development in rice .
- Rice SIZ1, a SUMO E3 ligase, controls spikelet fertility through regulation of anther dehiscence.Genetic results revealed the co-segregation of single T-DNA insertional recessive mutation with the observed phenotypes in siz1. In addition to showing reduced plant height, tiller number and seed set percentage, both the siz1 mutant and SIZ1-RNAi transgenic plants showed obvious defects in anther dehiscence, but not pollen viability. The anther indehiscence in siz1 was probably a result of defects in endothecium development before anthesis. Interestingly, rice orthologs of AtIRX and ZmMADS2, which are essential for endothecium development during anther dehiscence, were significantly down-regulated in siz1. Compared with the wild-type, the sumoylation profile of high-molecular-weight proteins in mature spikelets was reduced significantly in siz1 and the SIZ1-RNAi line with notably reduced SIZ1 expression. The nuclear localization signal located in the SIZ1 C-terminus was sufficient for its nuclear targeting in bombarded onion epidermis.The results suggest the functional role of SIZ1, a SUMO E3 ligase, in regulating rice anther dehiscence.
Heterologous expression of OsSIZ1, a rice SUMO E3 ligase, enhances broad abiotic stress tolerance in transgenic creeping bentgrass.
GO assignment(s): GO:0009901, GO:0009737, GO:0009651, GO:0009408, GO:0009409, GO:0016925
- In rice, SIZ1 was universally present in all examined tissues and all developmental stages (data not shown). Similar to most of the characterized and annotated SIZ/PIAS (SAP and MIZ/Protein Inhibitor of Activated STAT) SUMO E3 ligases from all organisms.
In Arabidopsis, AtSIZ1 protein is primarily localized in the nucleus, and PHR1, a MYB transcriptional activator, is its direct target in response to phosphate deficiency .Therefore, the subcellular localization is important to reveal the potential functions of rice SIZs. Recently, Park et al. (2010) showed the nuclear localization of OsSIZ1 and OsSIZ2 in rice protoplasts. To verify whether NLS in the SIZ1 C-terminus is responsible for its nuclear targeting, the NLS-containing C-terminal SIZ1 was fused to the N-terminus of eGFP for particle bombardment-mediated transient assay in onion epidermis (Fig. 1). The mRFP-tagged Ethylene Response Factor 4 (P35S::ERF4-mRFP:T35S), a known transcription factor, was used as a positive nuclear localization marker. Cells expressing the SIZ1–CT–eGFP fusion construct showed co-localization of GFP signals with ERF4 specifically in the nuclei (Fig. 3b). Our subcellular localization study suggested that the NLS-containing C-terminus of SIZ1 was sufficient for its nuclear targeting.
- Similar to most of the characterized and annotated SIZ/PIAS (SAP and MIZ/Protein Inhibitor of Activated STAT) SUMO E3 ligases from all organisms, rice SIZ1 also contains SAP, PINIT, SP-RING, a SUMO binding motif (hhhSXSaaa), a C-terminal nuclear localization signal (NLS) and the plant-specific PHD domain (plant homeodomain with C4HC3-type Zn-finger) (Fig. 2a,b). PINIT (Pro-Ile-Asn-Ile-Thr) and SP-RING, containing a zinc-finger (C2HC3), are essential for SUMO E3 ligase activity, and SAP (scaffold attachment factors SAF-A/B, Acinus, PIAS, a helix–extended loop–helix) forms a helix–extended loop–helix structure probably involved in DNA binding (Aravind & Koonin, 2000). Amino acid comparison revealed that all plant SIZs possess all consensus domains (Fig. 2b).
- A BlastP search analysis with SIZ1 amino acid sequences used as a query was employed to generate a rooted phylogenetic tree to illustrate the relationship of rice SIZs to their plant orthologs. As shown in Fig. S2c, rice SIZ1 and SIZ2 are positioned in different clades, and AtSIZ1 is closer to rice SIZ1 than to SIZ2.
- Sequence similarity analysis also confirmed that rice SIZ1 is closely related to AtSIZ1 (Fig. 2d). The amino acid sequences of SIZ1 and SIZ2 showed high similarity to sorghum loci Sb09g002225 and Sb08g000380, with 65.0% and 57.1% identity, respectively (data not shown). This is probably because both rice and sorghum originate from the grass family and have high synteny for sharing similar panicle architecture.
Labs working on this gene
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- Hyeong Cheol Park, Hun Kim, Sung Cheol Koo, Hee Jin Park, Mi Sun Cheong, Hyewon Hong, Dongwon Baek, Woo Sik Chung, Doh Hoon Kim, Ray A. Bressan, Sang Yeol Lee, Hans J. Bohnert, Dae-Jin Yun.Plant, Cell & Environment, 2010, 33(11): 1923-1934
- Huadun Wang, Kousar Makeen, Yan Yan, Yue Cao, Shubin Sun, Guohua Xu.Plant Molecular Biology Reporter, 2011, 29(2): 411-417 DOI: 10.1007/s11105-010-0232-y
- Saminathan Thangasamy, Cian-Ling Guo, Ming-Hsiang Chuang, Ming-Hsing Lai, Jychian Chen, Guang-Yuh Jauh.New Phytologist, 2011, 189(3): 869-882 DOI: 10.1111/j.1469-8137.2010.03538.x
- Zhigang Li, Qian Hu, Man Zhou, Joshua Vandenbrink, Dayong Li, Nick Menchyk, Shane Reighard, Ayla Norris, Haibo Liu, Dongfa Sun, Hong Luo Plant Biotechnology Journal, 2013, 11(4): 432-445 DOI: 10.1111/pbi.12030