Role of TRIPTYCHON in trichome patterning in Arabidopsis

Martina Pesch,Martin Hülskamp

doi:10.1186/1471-2229-11-130

Abstract

BackgroundTrichome patterning in Arabidopsis thaliana is governed by three types of activators, R2R3MYB, bHLH and WD40 proteins, and six R3MYB inhibitors. Among the inhibitors TRIPTYCHON (TRY) seems to fulfill a special function. Its corresponding mutants produce trichome clusters whereas all other inhibitors are involved in trichome density regulation.ResultsTo better understand the role of TRY in trichome patterning we analyzed its transcriptional regulation. A promoter analysis identified the relevant regulatory region for trichome patterning. This essential region contains a fragment required for a double negative feedback loop such that it mediates the repression of TRY/CPC auto-repression. By transforming single cells of pTRY:GUS lines with p35S:GL1, p35S:GL3 and p35S:TTG1 in the presence or absence of p35S:TRY or p35S:CPC we demonstrate that TRY and CPC can suppress the TRY expression without the transcriptional down regulation of the activators. We further show by promoter/CDS swapping experiments for the R3MYB inhibitors TRY and CPC that the TRY protein has specific properties relevant in the context of both, cluster formation and trichome density.ConclusionsOur identification of a TRY promoter fragment mediating a double negative feedback loop reveals new insight in the regulatory network of the trichome patterning machinery. In addition we show that the auto-repression by TRY can occur without a transcriptional down regulation of the activators, suggesting that the differential complex formation model has a biological significance. Finally we show that the unique role of TRY among the inhibitors is a property of the TRY protein.

Highlights

Trichome patterning in Arabidopsis thaliana is governed by three types of activators, R2R3MYB, basic helixloop-helix (bHLH) and WD40 proteins, and six R3MYB inhibitors
We tested whether the 3’ region or the introns are relevant for TRY function by transforming try mutant plants with a 1.8 kb 5’ region that was fused to the TRY CDS (Figure 1, pTRY-A, B:cTRY tryJC)
Because expression of a given construct is variable between different T2 lines we present pictures of the lines with the strongest expression only (Figure 2) and provide the percentage of lines in which the basal expression as well as trichome expression and those in which only the trichome specific expression is found after 24 hours of GUS staining (Figure 1B)

Summary

Introduction

Trichome patterning in Arabidopsis thaliana is governed by three types of activators, R2R3MYB, bHLH and WD40 proteins, and six R3MYB inhibitors. Its corresponding mutants produce trichome clusters whereas all other inhibitors are involved in trichome density regulation. The trichome position is not correlated with any recognizable leaf structures and clonal analysis excluded a cell lineage mechanism [5,6]. For these reasons, it is widely accepted that patterning is mediated by cellular interactions between initially equivalent cells [2,3,7]. Genetic screens have identified two classes of mutants governing this process. The following summary will only consider the most relevant players as judged by the

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