Os09g0434200

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As a RING finger E3 ligase gene, Oryza sativa Delayed Seed Germination 1 (OsDSG1), controls seed germination and stress responses in rice[1].

Annotated Information

Function

Figure 1. Working model of ABA-signaling pathway in germinating rice seeds.(from reference [1]).
  • Xpress-OsDSG1 proteins were seen as high-molecularmass ladders that are the characteristic of ubiquitination, whereas there was no ubiquitination signal in the absence of E1, E2 or ubiquitin,which indicating that OsDSG1 is an E3 ubiquitin ligase.
  • OsDSG1 is involved in ABA signaling ,which influences drought and salt stress.
  • OsDSG1 is a member of the ABA signaling group, encodes a deduced protein that carries a RING finger motif present in a class of E3 ligases. The protein sequence is highly homologous to Arabidopsis AIP2, which functions as an E3 ligase.
  • ABA signaling, including via OsDSG1, is the major determinant of germination success, and that an unknown regulatory trait

must control the overall ABA-signaling pathway in developing seeds[1].

GO assignment(s): GO:0005515, GO:0008270

Mutation

  • To verify that the mutant phenotype was indeed due to disruption of OsDSG1, we generated transgenic plants carrying the OsDSG1 RNA interference (RNAi) construct(Fig. 3a). Among five independent RNAi plants, three were selected for further analyses (Fig. 3b).
  • The osdsg1 T-DNA mutant and RNAi plants were tolerant to high salt and drought. Therefore, this mutant allele could be used for developing stress-tolerant cultivars. Because the trait is a loss-of-function mutation, it can be achieved via chemical mutagenesis or natural transposontagging, which does not involve gene manipulation[1].

Expression

Figure 1. Real-time PCR analyses of OsDSG1 transcript levels in seedlings .(from reference [1]).
  • Real-time PCR analyses indicated its presence in roots and leaves, with levels slowly decreasing as the plants matured (Fig. 1c). In

spikelets, expression was higher at 25 days after fertilization(DAF) than at 6 DAF (Fig. 1c). However, transcripts were markedly increased in seeds during germination (Fig. 1d). It's in agreement with those reported by Zhang et al.[2], where Arabidopsis AIP2 was expressed in various vegetative and reproductive organs.

  • Zhu[3] has reported that ABA influences the inhibitory effect of salts on germination. On regular MS media, the rate for the osdsg1 mutant was 70%, i.e., 20% lower than for WT seed(Fig. 5a). However, under salt stress (150 mM NaCl), the mutant germination rate was 5 times higher than for WT(Fig. 5a). Since salt stress induces ABA response, it is expected that germination rate of osdsg1 is further reduced under the stress condition. However, the mutant germinated better, probably due to increased tolerance of the seedlings to the salt stress.
  • Mutation in OsDSG1 increases expressions of OsABI5 and ABA-responsive genes. Park et al. examined transcript levels of two well-known ABA-responsive genes: RESPONSIVE TO DESSICATION29B (RD29B) and RESPONSIVE TO ABA18 (RAB18)[4]. Quantitative real-time PCR analyses showed that transcript levels of RD29B and RAB18 were elevated.

Evolution

OsDSG1 is homologous to AIP2, which negatively regulates ABA signaling by targeting ABI3 for post-translational destruction. Park et al. synthesized cDNA containing the full-length ORF and compared its sequence with genomic DNA. This gene consists of four exons and encodes a protein of 320 amino acid residues, which is most similar to Arabidopsis AIP2, an E3 ligase containing the RING finger motif. The proteins shared 41% sequence identity and 49% similarity. Alignment of the OsDSG1 protein with AIP2 showed that the C-terminal region containing the RING finger motif is most conserved[1][2].

Knowledge Extension

More than 387 members of RING finger genes occur in Arabidopsis, and 300 in rice, although it is not clear if all of those genes encode E3 ubiquitin ligases. Little is known about the functional roles of RING finger E3 ligase in rice. However, one such gene, OsBIRF1, causes a reduction in ABA sensitivity in the roots and increases drought tolerance during germination[5]. Oryza sativa Delayed Seed Germination 1 (OsDSG1) encodes a RING finger E3 ligase, which negatively regulates OsABI3.

Labs working on this gene

  • Crop Biotech Institute & Department of Plant Molecular Systems Biotechnology, Kyung Hee University, Yongin 446-701, Republic of Korea
  • Department of Plant Genetic Engineering, Catholic University of Daegu, Gyeongsan 712-702, Republic of Korea
  • Department of Life Science, Pohang University of Science and Technology (POSTECH), Pohang 790-784, Republic of Korea

References

  1. 1.0 1.1 1.2 1.3 1.4 1.5 Park G G, Park J J, Yoon J, et al. A RING finger E3 ligase gene, Oryza sativa Delayed Seed Germination 1 (OsDSG1), controls seed germination and stress responses in rice[J]. Plant molecular biology, 2010, 74(4-5): 467-478.
  2. 2.0 2.1 Zhang X, Garreton V, Chua N H. The AIP2 E3 ligase acts as a novel negative regulator of ABA signaling by promoting ABI3 degradation[J]. Genes & Development, 2005, 19(13): 1532-1543.
  3. Zhu J K. Salt and drought stress signal transduction in plants[J]. Annual review of plant biology, 2002, 53: 247.
  4. Wang Q, Guan Y, Wu Y, et al. Overexpression of a rice OsDREB1F gene increases salt, drought, and low temperature tolerance in both Arabidopsis and rice[J]. Plant molecular biology, 2008, 67(6): 589-602.
  5. Liu H, Zhang H, Yang Y, et al. Functional analysis reveals pleiotropic effects of rice RING-H2 finger protein gene OsBIRF1 on regulation of growth and defense responses against abiotic and biotic stresses[J]. Plant molecular biology, 2008, 68(1-2): 17-30.

Structured Information