Journal Article

Inhibition of shoot branching by new terpenoid plant hormones

Shirasu, Ken, Yoneyama, Koichi, Hanada, Atsushi, Yoshida, Satoko, Arite, Tomotsugu, Akiyama, Kohki, Takeda-Kamiya, Noriko, Umehara, Mikihisa, Magome, Hiroshi, Kamiya, Yuji

2008

Overview

Shoot branching is a major determinant of plant architecture and is highly regulated by endogenous and environmental cues. Two classes of hormones, auxin and cytokinin, have long been known to have an important involvement in controlling shoot branching. Previous studies using a series of mutants with enhanced shoot branching suggested the existence of a third class of hormone(s) that is derived from carotenoids, but its chemical identity has been unknown. Here we show that levels of strigolactones, a group of terpenoid lactones, are significantly reduced in some of the branching mutants. Furthermore, application of strigolactones inhibits shoot branching in these mutants. Strigolactones were previously found in root exudates acting as communication chemicals with parasitic weeds and symbiotic arbuscular mycorrhizal fungi. Thus, we propose that strigolactones act as a new hormone class—or their biosynthetic precursors—in regulating above-ground plant architecture, and also have a function in underground communication with other neighbouring organisms. Branching out: new class of plant hormones inhibits branch formation For many years the textbooks recognized five 'classic' plant hormones: auxin, gibberellins, ethylene, cytokinin and abscisic acid. To these can be added the brassinosteroids, nitric oxide and jasmonates, among others, as phytohormones or plant growth regulators. Shoot branching is regulated by hormones, with both auxin and cytokinin playing a part. But the existence of mutants with enhanced branching in several species suggested a third factor was involved, a novel plant hormone released from the roots that prevents excessive shoot branching. Two groups now identify a class of chemical compounds called strigolactones — or one of their derivatives — as that missing hormone. Strigolactones are found in root exudates and are reduced in the branching mutants; external application of these chemicals inhibits shoot branching in the mutants. Shoot branching is regulated by hormones. Branching mutants in several plant species suggests the existence of a plant hormone that is released from the roots and prevents excessive shoot branching. This paper reports on one of two studies that show that a class of chemical compounds called strigolactones found in root exudates are reduced in the branching mutants and that external application of these chemicals inhibits shoot branching in the mutants. It is proposed that strigolactones or related metabolites are the sought after class of hormones.

• Publisher: Nature Publishing Group UK,Nature Publishing,Nature Publishing Group
• Subject: Analysis / Arabidopsis / Arabidopsis - drug effects / Arabidopsis - genetics / Arabidopsis - growth & development / Biological and medical sciences / Biosynthesis / branching / Carotenoids / Chemical agents / chemistry / drug effects / Flowers & plants / Fundamental and applied biological sciences. Psychology / Fungi / Gene expression / Gene Expression Regulation, Plant / Genetic aspects / genetics / growth & development / Hormones / Humanities and Social Sciences / lactones / Lactones - analysis / Lactones - chemistry / Lactones - metabolism / Lactones - pharmacology / metabolism / multidisciplinary / Mutation / Oryza / Oryza - drug effects / Oryza - growth & development / Oryza - metabolism / Oryza - parasitology / Oryza sativa / Parasitism / Parasitism and symbiosis / parasitology / pharmacology / Plant Growth Regulators / Plant Growth Regulators - analysis / Plant Growth Regulators - chemistry / Plant Growth Regulators - metabolism / Plant Growth Regulators - pharmacology / Plant hormones / Plant physiology / Plant physiology and development / Plant Roots / Plant Roots - parasitology / Plant Shoots / Plant Shoots - drug effects / Plant Shoots - growth & development / rice / root exudates / Science / Science (multidisciplinary) / Seedlings / Seeds / shoots / Signal transduction / steroid lactones / Striga hermonthica / strigolactones / Symbiosis / Terpenes / Terpenes - analysis / Terpenes - chemistry / Terpenes - metabolism / Terpenes - pharmacology / terpenoids / tillering / Vegetative apparatus, growth and morphogenesis. Senescence