Amino acid substitutions in CPC-LIKE MYB reveal residues important for protein stability in Arabidopsis roots

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.

Ectopic Expression of JcCPL1, 2, and 4 Affects Epidermal Cell Differentiation, Anthocyanin Biosynthesis and Leaf Senescence in Arabidopsis thaliana

The CAPRICE (CPC)-like (CPL) genes belong to a single-repeat R3 MYB family, whose roles in physic nut (Jatropha curcas L.), an important energy plant, remain unclear. In this study, we identified a total of six CPL genes (JcCPL1–6) in physic nut. The JcCPL3, 4, and 6 proteins were localized mainly in the nucleus, while proteins JcCPL1, 2, and 5 were localized in both the nucleus and the cytoplasm. Ectopic overexpression of JcCPL1, 2, and 4 in Arabidopsis thaliana resulted in an increase in root hair number and decrease in trichome number. Consistent with the phenotype of reduced anthocyanin in shoots, the expression levels of anthocyanin biosynthesis genes were down-regulated in the shoots of these three transgenic A. thaliana lines. Moreover, we observed that OeJcCPL1, 2, 4 plants attained earlier leaf senescence, especially at the late developmental stage. Consistent with this, the expression levels of several senescence-associated and photosynthesis-related genes were, respectively, up-regulated and down-regulated in leaves. Taken together, our results indicate functional divergence of the six CPL proteins in physic nut. These findings also provide insight into the underlying roles of CPL transcription factors in leaf senescence.

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.

Localization of tomato (Solanum lycopersicum) R3 MYB protein encoded by SlTRY in Arabidopsis roots

CAPRICE (CPC), an R3-type MYB transcription factor, is known to promote root hair differentiation in the root epidermis of Arabidopsis. CPC moves from non-hair cells to adjacent hair-forming cells. In contrast, we have previously shown that there is no movement of the CPC homologs, ENHANCER OF TRY AND CPC 1, 2, and 3 (ETC1, 2, and 3), and TRYPTICHON (TRY) between root epidermal cells. We also identified a tomato homolog of CPC, named Solanum lycopersicumTRYPTICHON (SlTRY).SlTRY-introduced transgenic Arabidopsis produced many root hairs, like CPC-introduced transgenic Arabidopsis. To clarify the cell-to-cell movement ability of the SlTRY protein, in this study, we observed the distribution of GFP fluorescence in CPCp:SlTRY:GFP transgenic Arabidopsis. Unexpectedly, SlTRY moved from non-hair cells to adjacent root hair cells, like CPC, in Arabidopsis root epidermis. SlTRY does not have the cell-to-cell movement sequence (S1) defined in CPC, and the mechanism of movement is still unknown. Further investigation is necessary to elucidate the mechanism of cell-to-cell movement of SlTRY. Our results will help in the further unraveling of the functions of these MYB transcription factors in determining cell fate.