BRANCHED1: A Key Hub of Shoot Branching

Abstract

Shoot branching is a key process for plant growth and fitness. Newly produced axes result from axillary bud outgrowth, which is at least partly mediated through the regulation of BRANCHED1 gene expression (BRC1/TB1/FC1). BRC1 encodes a pivotal bud-outgrowth-inhibiting transcription factor belonging to the TCP family. As the regulation of BRC1 expression is a hub for many shoot-branching-related mechanisms, it is influenced by endogenous (phytohormones and nutrients) and exogenous (light) inputs, which involve so-far only partly identified molecular networks. This review highlights the central role of BRC1 in shoot branching and its responsiveness to different stimuli, and emphasizes the different knowledge gaps that should be addressed in the near future.

Keywords: TCP transcription factors; hormones; light; nutrients; regulation; shoot branching.

FIGURE 1

Many factors influence the expression of BRC1, including developmental, positional, genetic, hormonal, sugar signal and environmental factors. Auxin, cytokinin (CK), and strigolactone (SL) are implicated in the hormonal regulation of BRC1 expression; auxin and SLs as promoters of BRC1 and CKs as an inhibitor of BRC1. The red line, inhibition effect; the green arrow, stimulation effect; the yellow bullet-end lines, protein interaction; the violet element, plant hormones; the green element, plant nutrition; the green element, the yellow element, exogenous influence factor; the gray triangle, the proteins that interact with BRC1/TB1; D53, DWARF 53; HB21, HOMEOBOX PROTEIN 21; HB40, HOMEOBOX PROTEIN 40; HB53, HOMEOBOX PROTEIN 53; IPA1, IDEAL PLANT ARCHITECTURE1; NCED3, NINE-CIS-EPOXICAROTENOID DIOXIGENASE 3; PHYB, PHYTOCHROME B; T6P, trehalose-6 phosphate.