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The basic helix‐loop‐helix transcription factor BIS 2 is essential for monoterpenoid indole alkaloid production in the medicinal plant Catharanthus roseus
Author(s) -
Van Moerkercke Alex,
Steensma Priscille,
Gariboldi Ivo,
Espoz Javiera,
Purnama Purin C.,
Schweizer Fabian,
Miettinen Karel,
Vanden Bossche Robin,
De Clercq Rebecca,
Memelink Johan,
Goossens Alain
Publication year - 2016
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/tpj.13230
Subject(s) - catharanthus roseus , iridoid , ectopic expression , biochemistry , biology , transcription factor , chemistry , gene , botany , glycoside
Summary Monoterpenoid indole alkaloids ( MIA s) are produced as plant defence compounds. In the medicinal plant Catharanthus roseus , they comprise the anticancer compounds vinblastine and vincristine. The iridoid (monoterpenoid) pathway forms one of the two branches that feed MIA biosynthesis and its activation is regulated by the transcription factor ( TF ) basic helix‐loop‐helix ( bHLH ) iridoid synthesis 1 ( BIS 1). Here, we describe the identification and characterisation of BIS 2, a jasmonate ( JA )‐responsive bHLH TF expressed preferentially in internal phloem‐associated parenchyma cells, which transactivates promoters of iridoid biosynthesis genes and can homodimerise or form heterodimers with BIS 1. Stable overexpression of BIS 2 in C. roseus suspension cells and transient ectopic expression of BIS 2 in C. roseus petal limbs resulted in increased transcript accumulation of methylerythritol‐4‐phosphate and iridoid pathway genes, but not of other MIA genes or triterpenoid genes. Transcript profiling also indicated that BIS 2 expression is part of an amplification loop, as it is induced by overexpression of either BIS 1 or BIS 2 . Accordingly, silencing of BIS 2 in C. roseus suspension cells completely abolished the JA ‐induced upregulation of the iridoid pathway genes and subsequent MIA accumulation, despite the presence of induced BIS 1 , indicating that BIS 2 is essential for MIA production in C. roseus .