Os06g0499500

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Annotated Information

Function

The GH3 is a class of genes that respond to Auxin in some species of plants. The GH3 proteins in Arabidopsis have been shown to be involved in plant growth and development, photomorphogenesis, light- and auxin-signaling, and auxin homeostasis. GH3 proteins from Arabidopsis and rice could be divided into three and two groups, respectively. GH3 proteins classified in the same groups may have the similar functions in events common to both monocot and dicot plants. Group III GH3 proteins may have dicot-specific functions as they could not be identified from rice or other monocots. Organ-specific differential expression suggests diverse roles of these proteins during plant growth and development. The effect of light and auxin treatment on the transcript levels of OsGH3 genes implies their role in light and auxin signal transduction. The phenotypes of the insertion mutants of some GH3 genes showed dwarfism, sterility, vivipary, and leaf withering. From these phenotypes, it can be speculated that these genes may play a role in different metabolic pathways and cellular processes influenced by light and auxin. But whether the assumption that these phenotype changes are specific to insertional mutagenesis of OsGH3 gene still remains to be proven experimentally.

Expression

The expression of all the 12 OsGH3 genes was verified experimentally and quantitated by real-time PCR analysis in the present study. Many of the GH3 genes in Arabidopsis, soybean, and tobacco were found to be differentially expressed in different tissues or in response to exogenous auxin and light stimuli. To determine the organ-specific expression pattern of each OsGH3 gene, real-time PCR was performed with total RNA isolated from etiolated shoots, green shoots, roots, flowers, and callus. This analysis revealed that OsGH3 genes are differentially expressed in various tissues/organs. The transcription of OsGH3-12 was found to be root-specific and was hardly detectable in other tissues examined. However, OsGH3-10 was found to be expressed at very low levels in all the tissues. In contrast, other OsGH3 genes were found to be expressed in almost all the tissues examined but at different levels. Also, significant differences were found in the transcript abundance of OsGH3 genes in etiolated and green shoots, indicating their light regulation. The transcript levels of most of the OsGH3 genes were upregulated by auxin treatment, although to varying degree. The effect is more pronounced on OsGH3-1, -2, -4 and, to some extent, on OsGH3-8 too. The difference in the inducibility of individual GH3 genes is likely due to a variety of factors such as kinetics of induction, tissue-specific auxin reception, cell type-dependent and differential regulation of free auxin concentrations, or differentmodes of auxin-dependent transcriptional and posttranscriptional regulation.

Evolution

Two major groups (groups I and II), with very strong boot-strap support, were observed, which included four and eight OsGH3 proteins, respectively. Twelve OsGH3 proteins formed only three sister pairs. The sister pair OsGH3-1 and -4 was found to be present on duplicated chromosomal block 1 present between chromosomes 1 and 5 as described by Paterson et al (2004). However, the sister pair OsGH3-9 and -10 may represent a local duplication event. The third sister pair (OsGH3-3 and -12) may also be present on unidentified duplicated chromosomal block. Taken together, these observations throw some light on the diversification of rice GH3 genes during evolution. The Arabidopsis GH3 proteins have been classified into three groups on the basis of their protein structure and specificity to adenylate plant hormones (Staswick et al 2002). To examine protein relationships of rice and Arabidopsis. GH3 proteins, an unrooted tree was constructed from alignments of their full-length GH3 protein sequences. Based upon the sequence homology, all the rice and Arabidopsis GH3 proteins clustered distinctly into three groups (I, II, and III). Group I consisted of only six members, four from rice cluster, i.e., OsGH3-3, -5, -6, and -12, along with AtGH-10 and -11. AtGH3-11 (JAR1/FIN219) has been shown to adenylate jasmonic acid (JA) (Staswick et al. 2002). Seven of the OsGH3 proteins belonged to group II AtGH3 proteins, which are involved in IAA adenylation (Staswick et al. 2002). The group II Arabidopsis GH3 genes encode IAA-amido synthetases that conjugate amino acids to IAA and regulate plant growth and development (Staswick et al. 2005). However, group III included only Arabidopsis GH3 proteins with unknown function, which do not adenylate IAA, JA, or SA. Surprisingly, no group III GH3 protein could be identified in rice sequence databases searched. It can be speculated that group III GH3 proteins were lost in rice after divergence of monocots and dicots or evolved in dicots after the divergence from monocots and may perform dicot-specific functions. However, OsGH3-7 grouped with group II rice GH3 proteins, but did not group with Arabidopsis group II GH3 proteins.

Labs working on this gene

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References

The auxin-responsive GH3 gene family in rice (Oryza sativa) Functional & Integrative Genomics, 2006, 6(1): 36-46