Plant and Cell Physiology Advance Access originally published online on January 16, 2008
Plant and Cell Physiology 2008 49(2):157-169; doi:10.1093/pcp/pcn009
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Functional Differentiation of Lotus japonicus TT2s, R2R3-MYB Transcription Factors Comprising a Multigene Family
1Department of Biology, Ochanomizu University, Tokyo, 112-8610 Japan
2Kazusa DNA Research Institute, Chiba, 292-0812 Japan
*Corresponding author: E-mail, msakuta{at}cc.ocha.ac.jp; Fax, +81-3-5978-5712.
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Abstract |
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Leguminous plants have many paralogous genes encoding enzymes involved in the flavonoid biosynthetic pathway. Duplicate genes are predicted to contribute to the production of various flavonoid compounds and to have resulted in a diversity of legume species. We identified gene duplication in the transcription factors regulating flavonoid biosynthesis in the model legume Lotus japonicus. Three copies of a homolog of Arabidopsis thaliana TRANSPARENT TESTA2 (TT2), which is a MYB transcription factor that regulates proanthocyanidin biosynthesis, were present in the L. japonicus genome. The organ specificity and stress responsiveness differed among the three LjTT2s, and correlations between proanthocyanidin accumulation and the expression levels of LjTT2s were observed during seedling development. Moreover, three LjTT2s functionally complemented TT2 in transient expression experiments in A. thaliana leaf cells. The different reporter activity caused by LjTT2a was consistent with the affinity of physical interactions with TT8 and TTG1 in yeast two-hybrid experiments as well as the branching pattern of the phylogenetic tree. These results suggest that LjTT2 factors have diverse functions in the tissues in which they are expressed; in particular, LjTT2a is predicted to have evolved flexibility in interaction with other transcription regulators to resist environmental stresses.
Keywords: Lotus japonicus - Multigene family - MYB - Proanthocyanidin - Transcription factor
Abbreviations: AD, activation domain; ANR, anthocyanidin reductase; BD, binding domain; bHLH, basic helix–loop–helix; DMACA, 4-(dimethylamino) cinnamaldehyde; EST, expressed sequence tag; GFP, green fluorescent protein; LAR, leucoanthocyanidin reductase; LUC, firefly luciferase; ORF, open reading frame; RT–PCR, reverse transcription–PCR; RUC, Renilla luciferase; 35S, cauliflower mosaic virus 35S promoter; TAC, transformation-competent artificial chromosome; TT2, TRANSPARENT TESTA2; TT8, TRANSPARENT TESTA8; TTG1, TRANSPARENT TESTA GLABRA1
(Received December 12, 2007; Accepted January 10, 2008)
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