Abstract
In this study, we isolated a WD40-repeat gene from Artemisia annua glandular trichomes. This gene shows 69.97% sequence similarity to Arabidopsis TTG1 at aminoacid level. Sub-cellular localization study shows that AaWD40 protein diffuses in both cell nucleus and cytosol. The correct nuclear localization of AaWD40 was observed when co-expressed with AabHLH, a putative A. thaliana AtTTG1 homologue cloned from Artemisia annua glandular trichomes. When AaWD40 gene was ectopically over expressed in Arabidopsis transparent testa glabrous1-1 (ttg1-1) mutants of A. thaliana, PAs production in seeds was restored, and the trichomeless phenotypes of mutant were rescued. Real-time PCR analysis results revealed that ETC1, CPC, TTG2 and BAN (the downstream targets of AtTTG1 depend on regulatory complex), which regulate the epidermal differentiation and anthocyanin biosynthesis were differentially expressed as a result of AaWD40 over expression. Furthermore, the CLV1, CLV2, CLV3 and WUS, which are required to maintain the stem-cell niche of Arabidopsis shoot apex, were also modulated by AaWD40 and Arabidopsis TTG1. The transcriptions of AP2/ERF, bHLH, MYB, WRKY and NACs family proteins, which are mostly involved in defense, stress response and development regulation, were remarkably modulated by AaWD40 over expression. We hypothesize that WD40 repeat proteins act as a crucial factor in regulating a wide variety of cellular functions in A. thaliana.
Highlights
TWD repeat (WDR) proteins are characterized by 4 - 16 tandem WD motifs, which comprise 44 - 60 residue sequence typically delineated by the Gly-His (GH) dipeptide 11 - 24 residues from its N-terminus and ending in Trp-Asp (WD) dipeptide
It is believed that Arabidopsis TTG1 and the R2R3-MYB transcription factor GLABRA1 (GL1) [7] bind simultaneously to the basic helix-loop-helix proteins GLABRA3 (GL3) and ENHANCER OFGLABRA3 (EGL3) [8] to form a trimeric regulatory complex, thereby activating the transcription of downstream genes controlling epidermal differentiation and anthocyanin biosynthesis
We found that over-expression of analysis of a WD40 repeat protein (AaWD40) can fully rescue the trichomeless and PA phenotype in Arabidopsis ttg1-1 mutant
Summary
TWD repeat (WDR) proteins are characterized by 4 - 16 tandem WD ( called Trp-Asp or WD-40) motifs, which comprise 44 - 60 residue sequence typically delineated by the Gly-His (GH) dipeptide 11 - 24 residues from its N-terminus and ending in Trp-Asp (WD) dipeptide. One of the most well studied WDR proteins is TRANSPARENT TESTA GLABRA1 (AtTTG1), which regulates several developmental and biochemical pathways, including the formation of root hair, differentiation of trichome and the production of seed mucilage and anthocyanin pigments in Arabidopsis [3]-[5]. It is believed that Arabidopsis TTG1 and the R2R3-MYB transcription factor GLABRA1 (GL1) [7] bind simultaneously to the basic helix-loop-helix (bHLH) proteins GLABRA3 (GL3) and ENHANCER OFGLABRA3 (EGL3) [8] to form a trimeric regulatory complex, thereby activating the transcription of downstream genes controlling epidermal differentiation and anthocyanin biosynthesis. One possible explanation is that the perturbation of flavonoids may directly affect auxin movement and cause the developmental abnormality [10], it is still unclear whether flavonoids act directly as regulatory agents or indirectly through auxin accumulation or movement, or alternatively, TTG1 may regulate the shoot development directly
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