Phytohormone inhibitor treatments phenocopy brassinosteroid–gibberellin dwarf mutant interactions in maize

Abstract

SummaryPhytohormone biosynthesis produces metabolites with profound effects on plant growth and development. Modulation of hormone levels during developmental events, in response to the environment, by genetic polymorphism, or by chemical application, can reveal the plant processes most responsive to a phytohormone.Applications of chemical inhibitors and subsequent measurements of specific phytohormones can determine whether, and which, phytohormone is affected by a molecule. In many cases, the sensitivity of biochemical testing has determined multiple pathways affected by a single inhibitor. Genetic studies are not subject to this problem, and a wealth of data about the morphological impacts of hormone biosynthetic inhibition have accumulated through the study of enzyme mutants. In this work, we sought to assess the specificity of three triazole inhibitors of cytochrome P450s by determining their abilities to recapitulate the phenotypes of single and double mutants affected in the production of brassinosteroid (BR) and gibberellin (GA) biosynthesis. The GA biosynthetic inhibitors uniconazole (UCZ) and paclobutrazol (PAC) were applied to the BR biosynthetic mutant nana plant2 (na2), and all doublemutant phenotypes were recovered in the UCZ treatment. PAC was unable to suppress the retention of pistils in the tassels of na2 mutant plants. The BR biosynthetic inhibitor propiconazole (PCZ) suppressed tiller outgrowth in the GA biosynthetic mutant dwarf5 (d5). All treatments were additive with genetic mutants for effects on plant height. Due to additional measurements performed here but not in previous studies of the double mutants, we detected new interactions between GA and BR biosynthesis affecting the days to tassel emergence and tassel branching. These experiments, a refinement of our previous model, and a discussion of the extension of this type of work are presented.

A genome-wide association study reveals a novel regulator of ovule number and fertility in Arabidopsis thaliana

“…Classic experiments in Vicia faba showed that auxin produced in the shoot apex inhibits axillary meristems[38], and more recently strigolactones were identified as graft-transmissible suppressors of branching (reviewed in [39]). Gibberellins also repress shoot branching in Arabidopsis, maize, and rice, with GA-deficient mutants displaying increased branching compared to wild-type controls[40–43]. In contrast, cytokinins and brassinosteroids are both positive regulators of branching[42–46].…”

Effects of propiconazole on rice growth and gene expression in response to nitrogen and phosphorus deficiencies

“…Moreover, the PPZ-treated plants displayed several phenotypes common to BR-deficient or signaling mutants, including dwarf shoots, short roots, and dark green leaves [18,25,26]. The reduction in growth observed in this study is likely due to reduced endogenous BR levels by PPZ inhibiting the BR biosynthesis enzymes [18,27]. Transcript levels of the BR biosynthesis genes (OsDWF4, OsD2, and OsCYP85A1), which are feedback-regulated by the BR signaling pathway [28], showed significant upregulation (Fig.…”

Inhibitors of Brassinosteroid Biosynthesis and Signal Transduction

“…Application of 10 nM BL reverted hypocotyl length to untreated values while 1 µM GA 3 had a minute effect, confirming that BR but not GA biosynthesis is targeted [167]. Inhibition of BR biosynthesis was also observed in A. thaliana and in Zea mais [213,254]. For the latter a strong dependency on the genetic background was observed [254].…”

“…Min et al used uniconazole and the structurally similar triazole paclobutrazol, another growth retardant inhibiting GA biosynthesis [213], as lead compounds for identification of specific and potent BR biosynthesis inhibitors [214]. The obtained products were first tested for inhibition of GA biosynthesis using a rice stem elongation assay since it was thought at that time that rice stem elongation depends only on GAs but not on BRs.…”