Complementation and protein localization analyses of R3 MYBs in an Arabidopsis caprice mutant.

Root hairs play vital roles in plant growth since they enable the efficient absorption of water and nutrients from the soil. Recent advances in Arabidopsis research have provided a deeper understanding of the molecular genetic mechanisms underlying root hair differentiation. CAPRICE (CPC) and its four homologs, which belong to the CPC gene family and encode R3 MYB transcription factors, play central roles in root hair differentiation. In this study, to better understand the functional specificity and contribution of these five CPC family genes, we conducted phenotypic and expression analyses of the CPC family proteins in a cpc mutant background. As a result, ENHANCER OF TRY AND CPC1 (ETC1) and ETC3 were found to complement the hairless root phenotype of the cpc mutant, as did CPC, whereas TRIPTYCHON (TRY) and ETC2 did not rescue the cpc phenotype. Protein expression analysis revealed that GFP fluorescence was nearly undetectable in pCPC::TRY:GFP/cpc and pCPC::ETC2:GFP/cpc plants, supporting the incapability of root hair formation in these plants. Interestingly, the fluorescence intensity of the CPC:GFP fusion protein was weaker than that of ETC1:GFP and ETC3:GFP fusion proteins. These results were inconsistent with the result of the phenotypic analysis, in which the three genes promoted root hair formation to almost the same degree in the cpc mutant background. We further discuss the discrepancy between the root hair phenotypes and the expression levels of CPC family proteins.

Identification of six CPC-like genes and their differential expression in leaves of tea plant, Camellia sinensis.

Tea is one of the most consumed beverages worldwide, and trichome formation in tea plant leaves impairs their commercial value. In Arabidopsis thaliana leaves, trichome formation is negatively regulated by the CPC family genes, which encode R3-type MYB transcription factors. Here, we identified six CPC-like genes in a tea plant (Camellia sinensis var. sinensis) for the first time. Simulated three-dimensional structure of the MYB domains of all the six CPC-like proteins exhibited negative charge on the surface, as observed on that of the Arabidopsis CPC protein that does not bind to DNA, indicating their similarity with regard to molecular interaction. We further found that the six CPC-like genes were differentially expressed in different developmental stages of tea leaves, and four out of the six genes were upregulated in the youngest 1st leaves, which formed more trichomes than other older leaves. Although it does not establish a causal link, the correlation between differential expression of CPC-like genes and variable trichome formation suggests that the R3-type MYB transcription factors are potential precipitating factors in affecting the value of tea leaf.

Function of the TRY C-terminal region artificially fused with its homologous transcription factors inducing root hair differentiation in Arabidopsis.

TRIPTYCHON (TRY) is one of the R3-MYB transcription factors. Its extended C-terminal 19 amino-acid region (CTRY) is considered to affect the ability of root hair differentiation in Arabidopsis. Here, to further understand the function of CTRY, it, together with GFP, was artificially fused with TRY homologs, CPC and ETC1, which do not contain such extended regions and induce root hair differentiation. Arabidopsis transgenic plants carrying the fusion proteins, CPC-CTRY-GFP and ETC1-CTRY-GFP, induced root hair differentiation as observed in those carrying the original proteins without CTRY. The expression levels of the fusion proteins in the transgenic plants were essentially the same as those of the original proteins, although their subcellular localization to nuclei of root epidermal cells was slightly changed by CTRY. Therefore, CTRY does not affect the ability of CPC and ETC1 to induce root hair differentiation when artificially fused, and its function may be restricted in TRY.