The basic helix‐loop‐helix transcription factor BIS2 is essential for monoterpenoid indole alkaloid production in the medicinal plant Catharanthus roseus. (13th August 2016)

• Record Type: Journal Article
• Authors: 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
• Is Part Of: Plant journal. Volume 88:Number 1(2016:Oct.)
• Page Start: 3
• Page End: 12
• Publication Date: 2016-08-13
• Subjects: basic helix‐loop‐helix -- Catharanthus roseus -- Madagascar periwinkle -- jasmonate -- terpenoid -- iridoid -- monoterpenoid -- alkaloid; Plant molecular biology -- Periodicals; Plant cells and tissues -- Periodicals; Botany -- Periodicals; 580
• DOI: 10.1111/tpj.13230
• Languages: English
• ISSNs: 0960-7412

Abstract

Summary: Monoterpenoid indole alkaloids (MIAs) 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 (BIS1). Here, we describe the identification and characterisation of BIS2, 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 BIS1. Stable overexpression of BIS2 in C. roseus suspension cells and transient ectopic expression of BIS2 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 BIS2 expression is part of an amplification loop, as it is induced by overexpression of either BIS1 or BIS2 . Accordingly, silencing of BIS2 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 BIS1, indicating that BIS2 is essential for MIA production in C. roseus . Significance Statement: Madagascar periwinkle produces the valuable anticancer therapeutic compounds vinblastine and vincristine.The biosynthesis of these monoterpenoid indole alkaloids is strictly controlled by developmental and environmental cues. Here we describe the identification of a transcriptional regulator invovled in the jasmonate‐dependent activation and amplification loop governing one specific branch of the monoterpenoid indole alkaloid pathway.