Os06g0127800

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Annotated Information

Function

DLT,a GRAS protein,was identified to be involved in rice BR signaling.The brassinosteroid (BR) response is fine-tuned by multiple strategies.Transcription analysis of most known BR-related genes, including biosynthetic genes, signaling genes and also several downstream BR responsive genes, reveals DLT has extensive effects on BR-related genes expression, indicating its important role in modulating BR response. By promoter and protein sequence analysis, a complicated and subtle network was proposed that DLT may be involved in fine-modulating BR response at both transcriptional and protein levels.Function of DLT seems very similar to OsBZR1.Both of them play dual roles in mediating upstream signaling to activate downstream gene expression, and in addition inhibiting the expression of BR biosynthetic genes.This gives out the possibility that DLT may interact with OsBZR1 directly to form protein complex to execute their regulatory functions. However,yeast two-hybrid tests disaffirmed this presumption. It is interesting that three BRREs (BR-Response Elements) and two E-boxes were found in DLT promoter, implying the role of DLT as the potential target of OsBZR1 which could possibly both repress and activate its transcription.Our data also suggest that DLT and OsBZR1 regulate each other in opposite ways: while OzBZR1 binds to DLT promoter to inhibit its expression, DLT seems to promote OsBZR1 expression, indicating that the complex regulatory network may be necessary for the fine-tuning of BR response.

Expression

overexpression of a positive signaling gene, DLT, leads to confused phenotype, with either slightly higher or even shorter than wild-type, implying the insensitivity to a certain extent of rice cell elongation/division to alteration of endogenous BR level. It was believed that rice adopts a subtle and complicated mechanism to fine-tune the plant response to BR, either exogenous or endogenous.

Evolution

At transcriptional level, mediating through DLT and OsBZR1, BR response can feedback-regulate both the BR biosynthetic gene expression and BR signaling gene expression. While at the same time, DLT and OsBZR1 themselves are regulated each other. This compensation mechanism used to balance the BR response may partially explain that the change folds of the whole genome gene expression caused by BR deficiency or BR treatment are comparably very modest, as indicated by several microarray tests in Arabidopsis,which is quite different from observed in other phytohormone treatments. With respect to protein level, DLT could be phosphorylated, subcellular transported, interacted with other proteins or degraded,11 representing multiple strategies for hormone signaling. The subtle network may provide some cues for the tricky response of rice to increased exogenous or endogenous BR level. Whatever is true or not, this deduction provides new insights into BR signaling pathway in rice, and also direct our further efforts to testify this hypothesis to finally uncover the underlying mechanism of rice fine modulation on BR response.

Labs working on this gene

State Key Laboratory of Plant Genomics and National Center for Plant Gene Research

References

1. Yang G, Komatsu S. Molecular cloning and characterization of a novel brassinolide enhanced gene OsBLE1 in Oryza sativa seedlings. Plant Physiol Biochem 2004; 42:1-6. 2. Wu CY, Trieu A, Radhakrishnan P, Kwok SF, Harris S, Zhang K, et al. Brassinosteroids regulate grain filling in rice. Plant Cell 2008; 20:2130-45. 3. Tong H, Jin Y, Liu W, et al. DWARF AND LOW-TILLERING,a new member of GRAS family, plays positive roles in brassinosteroid signaling in rice.Plant J 2009; In Press (DOI: 10.1111/j.1365-313X.2009.03825.x.). 4. Bai MY, Zhang LY, Gampala SS, Zhu SW, Song WY, Chong K, Wang ZY. Functionsof OsBZR1 and 14-3-3 proteins in brassinosteroid signaling in rice. Proc Natl Acad SciUSA 2007; 104:13839-44. 5. He JX, Gendron JM, Sun Y, Gampala SS, Gendron N, Sun CQ, Wang ZY. BZR1 is a transcriptional repressor with dual roles in brassinosteroid homeostasis and growth responses. Science 2005; 307:1634-8. 6. Gendron JM, Wang ZY. Multiple mechanisms modulate brassinosteroid signaling. Curr Opin Plant Biol 2007; 10:436-41.