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TT2, TT8, and TTG1 synergistically specify the expression of BANYULS and proanthocyanidin biosynthesis in Arabidopsis thaliana
Author(s) -
Baudry Antoine,
Heim Marc A.,
Dubreucq Bertrand,
Caboche Michel,
Weisshaar Bernd,
Lepiniec Loïc
Publication year - 2004
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/j.1365-313x.2004.02138.x
Subject(s) - arabidopsis thaliana , myb , ectopic expression , biology , microbiology and biotechnology , arabidopsis , gene , gene expression , genetics , mutant
Summary Genetic analyses have demonstrated that together with TTG1, a WD‐repeat (WDR) protein, TT2 (MYB), and TT8 (bHLH) are necessary for the correct expression of BANYULS ( BAN ). This gene codes for the core enzyme of proanthocyanidin biosynthesis in Arabidopsis thaliana seed coat. The interplays of TT2, TT8, and their closest MYB/bHLH relatives, with TTG1 and the BAN promoter have been investigated using a combination of genetic and molecular approaches, both in yeast and in planta . The results obtained using glucocorticoid receptor fusion proteins in planta strongly suggest that TT2, TT8, and TTG1 can directly activate BAN expression. Experiments using yeast two‐ and three‐hybrid clearly demonstrated that TT2, TT8, and TTG1 can form a stable ternary complex. Furthermore, although TT2 and TT8 were able to bind to the BAN promoter when simultaneously expressed in yeast, the activity of the complex correlated with the level of TTG1 expression in A. thaliana protoplasts. In addition, transient expression experiments revealed that TTG1 acts mainly through the bHLH partner (i.e. TT8 or related proteins) and that TT2 cannot be replaced by any other related A. thaliana MYB proteins to activate BAN . Finally and consistent with these results, the ectopic expression of TT2 was sufficient to trigger BAN activation in vegetative parts, but only where TTG1 was expressed. Taken together, these results indicate that TT2, TT8, and TTG1 can form a ternary complex directly regulating BAN expression in planta .