The tandem complex of BEL and KNOX partners is required for transcriptional repression of ga20ox1

Abstract

SummaryTwo interacting three amino acid loop extension (TALE) proteins of potato, StBEL5 (Solanum tuberosom BEL 5) and POTH1 (potato homeobox 1), mediate developmental processes by regulating phytohormone levels. Overexpression of either partner alone increased tuber yields by lowering gibberellin (GA) levels and increasing cytokinins. Gel shift assays demonstrated that StBEL5 and POTH1 bind to the regulatory region of ga20 oxidase1 (ga20ox1 ) from potato, a gene encoding a key enzyme in the GA biosynthetic pathway. In tandem, StBEL5 and POTH1 had a greater binding af®nity for the ga20ox1 promoter than either protein alone. The StBEL5±POTH1 heterodimer bound speci®cally to a composite 10-bp sequence, containing two TGAC cores. Using a transcription assay, StBEL5 and POTH1 suppressed the activity of the ga20ox1 promoter by more than 50%. Dominant negative constructs containing the protein-binding domains of StBEL5 or POTH1 blocked the repression activity of StBEL5 or POTH1, respectively. The mutated ga20ox1 promoter that could be bound by the StBEL5 or POTH1 proteins individually but not by the StBEL5±POTH1 heterodimer also abolished the repression activity of StBEL5, POTH1, and the StBEL5±POTH1 heterodimer. These results indicate that the tandem interaction of StBEL5 and POTH1 is essential for regulation of the expression of their target gene.

Accumulation of BEL1-like transcripts in solanaceous species

“…In this report, the observation that KNOTTED1-like mRNAs of potato are present in the phloem at the same time and location as the mRNAs from their protein partners of the BEL1-like family is intriguing. As previously reported (Chen et al 2004), the tandem complex consisting of both protein types was necessary for regulating transcriptional activity in a target gene that affected tuber formation.…”

“…Previous research in our lab suggests a BEL1-like TF, S. tubersosum BEL5, plays a role in tuber formation by forming a heterodimer with a KNOTTED1-like TF, POTH1, and binding to the promoter of ga20 oxidase1 to down-regulate its giberellic acid activity (Chen et al 2004). Subsequently cytokinin levels are enhanced and the result of this pathway is enhanced tuber formation (Banerjee et al 2006).…”

The Multiple Signals That Control Tuber Formation

“…Related genes from the TALE class in animals also control important processes of growth and differentiation (Machon et al, 2015;Marcos et al, 2015;Merabet and Galliot, 2015;Villaescusa et al, 2016). The physical interaction between KNOX and BEL1 proteins and its functional significance have been documented in numerous plant species (Bellaoui et al, 2001;Müller et al, 2001;Smith et al, 2002;Chen et al, 2003Chen et al, , 2004.…”

KNOX genes: versatile regulators of plant development and diversity

“…In some instances, however, the regulation of different morphologies by KNOX modules may reflect underlying homologies between structures. For example, tuber development in potato is regulated in part by an antagonistic interaction between KNOX and GA, probably reflecting the fact that tubers are modified shoots (Chen et al, 2004).…”