Strigolactones are positive regulators of light-harvesting genes in tomato

Abstract

Strigolactones are newly identified plant hormones, shown to participate in the regulation of lateral shoot branching and root development. However, little is known about their effects on biological processes, genes, and proteins. Transcription profiling of roots treated with GR24, a synthetic strigolactone with proven biological activity, and/or indole acetic acid (IAA) was combined with physiological and transcriptional analysis of a tomato mutant (Sl-ORT1) deficient in strigolactone production. GR24 treatment led to markedly induced expression of genes putatively involved in light harvesting. This was apparent in both the presence and absence of exogenously applied IAA, but not with IAA treatment alone. Following validation of the microarray results, transcriptional induction by light of the GR24-induced genes was demonstrated in leaves exposed to high or low light intensities. Sl-ORT1 contained less chlorophyll and showed reduced expression of light harvesting-associated genes than the wild type (WT). Moreover, perfusion of GR24 into WT and Sl-ORT1 leaves led to induction of most of the examined light harvesting-associated genes. Results suggest that GR24 treatment interferes with the root's response to IAA treatment and that strigolactones are potentially positive regulators of light harvesting in plants.

Fig. 1.

Intersection of significantly and differentially regulated gene lists. Differentially regulated genes were identified from hybridization data of roots exposed to GR24 and IAA treatments [IAA (10⁻⁸ M), IAA (10⁻⁸ M)+GR24 (13.5 μM), and GR24 (27 μM)] versus non-treated controls. The intersection area presents the number of genes differentially regulated for each of the treatments. (a) Up-regulated genes, (b) down-regulated genes.

Fig. 2.

Illustration of the light reaction-associated biological pathways in which differentially regulated genes putatively participate. Differentially regulated genes were identified from hybridization data of roots exposed to GR24 and IAA treatments [IAA (10_8 M), IAA (10_8 M)+GR24 (13.5 lM), and GR24 (27 lM)] versus non-treated controls. Blue or red squares represent individual genes. The colour within the squares represents fold change in gene expression in treatments versus controls; values of fold change are as indicated in the colour scale. Chl signifies chlorophyll. The figure was adapted from MapMan software (Thimm et al., 2004).