Functional characterization of TRICHOMELESS2, a new single-repeat R3 MYB transcription factor in the regulation of trichome patterning in Arabidopsis

Lijun Gan,Jin-Gui Chen,Kai Xia,Shucai Wang

doi:10.1186/1471-2229-11-176

Abstract

BackgroundSingle-repeat R3 MYB transcription factors (single-repeat MYBs) play important roles in controlling trichome patterning in Arabidopsis. It was proposed that single-repeat MYBs negatively regulate trichome formation by competing with GLABRA1 (GL1) for binding GLABRA3/ENHANCER OF GLABRA3 (GL3/EGL3), thus inhibiting the formation of activator complex TTG1(TRANSPARENT TESTA GLABRA1)-GL3/EGL3-GL1 that is required for the activation of GLABRA2 (GL2), whose product is a positive regulator of trichome formation. Previously we identified a novel single-repeat MYB transcription factor, TRICHOMELESS1 (TCL1), which negatively regulates trichome formation on the inflorescence stems and pedicels by directly suppressing the expression of GL1.ResultsWe analyzed here the role of TRICHOMELESS2 (TCL2), a previously-uncharacterized single-repeat MYB transcription factor in trichome patterning in Arabidopsis. We showed that TCL2 is closely related to TCL1, and like TCL1 and other single-repeat MYBs, TCL2 interacts with GL3. Overexpression of TCL2 conferred glabrous phenotype while knockdown of TCL2 via RNAi induced ectopic trichome formation on the inflorescence stems and pedicels, a phenotype that was previously observed in tcl1 mutants. These results suggested that TCL2 may have overlapping function with TCL1 in controlling trichome formation on inflorescences. On the other hand, although the transcription of TCL2, like TCL1, is not controlled by the activator complex formed by GL1 and GL3, and TCL2 and TCL1 proteins are more than 80% identical at the amino acid level, the expression of TCL2 under the control of TCL1 promoter only partially recovered the mutant phenotype of tcl1, implying that TCL2 and TCL1 are not fully functional equivalent.ConclusionsTCL2 function redundantly with TCL1 in controlling trichome formation on inflorescences, but they are not fully functional equivalent. Transcription of TCL2 is not controlled by activator complex formed by GL1 and GL3, but MIR156 controlled SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) transcription factors. However, SPLs might require co-activators to regulate the expression of their target genes, including TCL1, TRY and possibly, TCL2.

Highlights

Single-repeat R3 MYB transcription factors play important roles in controlling trichome patterning in Arabidopsis
We showed that MIR156 is involved in the regulation of TCL2, and SQUAMOSA PROMOTER BINDING PROTEIN LIKE (SPL) may require co-activators to regulate the expression of their target genes, including TCL1, TRY, and possibly, TCL2
By using a protoplast transfection system, we showed that TCL2 interacts with GL3 (Figure 6A), suggesting that TCL2 could block the formation of the activator complex required for trichome formation

Summary

Introduction

Single-repeat R3 MYB transcription factors (single-repeat MYBs) play important roles in controlling trichome patterning in Arabidopsis. Single-repeat R3 MYBs can move from a trichome precursor cell to its neighboring cells to block the formation of the activator complex by competing with GL1 in binding GL3 or EGL3, inhibiting trichome formation in shoots [8,13,18,19]. These single-repeat R3 MYB transcription factors differ in their binding strength to GL3 and their capacity to compete with GL1 for binding GL3. A protoplast transfection assay showed that TCL1 is stronger than CPC in their ability to bind GL3 [19]

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Discussion

Conclusion