A tomato strigolactone-impaired mutant displays aberrant shoot morphology and plant interactions

Abstract

Strigolactones are considered a new group of plant hormones. Their role as modulators of plant growth and signalling molecules for plant interactions first became evident in Arabidopsis, pea, and rice mutants that were flawed in strigolactone production, release, or perception. The first evidence in tomato (Solanum lycopersicon) of strigolactone deficiency is presented here. Sl-ORT1, previously identified as resistant to the parasitic plant Orobanche, had lower levels of arbuscular mycorrhizal fungus (Glomus intraradices) colonization, possibly as a result of its reduced ability to induce mycorrhizal hyphal branching. Biochemical analysis of mutant root extracts suggested that it produces only minute amounts of two of the tomato strigolactones: solanacol and didehydro-orobanchol. Accordingly, the transcription level of a key enzyme (CCD7) putatively involved in strigolactone synthesis in tomato was reduced in Sl-ORT1 compared with the wild type (WT). Sl-ORT1 shoots exhibited increased lateral shoot branching, whereas exogenous application of the synthetic strigolactone GR24 to the mutant restored the WT phenotype by reducing the number of lateral branches. Reduced lateral shoot branching was also evident in grafted plants which included a WT interstock, which was grafted between the mutant rootstock and the scion. In roots of these grafted plants, the CCD7 transcription level was not significantly induced, nor was mycorrhizal sensitivity restored. Hence, WT-interstock grafting, which restores mutant shoot morphology to WT, does not restore mutant root properties to WT. Characterization of the first tomato strigolactone-deficient mutant supports the putative general role of strigolactones as messengers of suppression of lateral shoot branching in a diversity of plant species.

Strigolactone Biosynthesis in Medicago truncatula and Rice Requires the Symbiotic GRAS-Type Transcription Factors NSP1 and NSP2

“…SLs are stimuli for mycorrhizal hyphae, and SL biosynthesis knockout mutants in tomato (ort1) and pea (Pisum sativum; ccd8) display a reduction in mycorrhizal root colonization (GomezRoldan et al, 2008;Koltai et al, 2010). The M. truncatula nsp1 nsp2 double mutant has a similar reduction in mycorrhizal root infection ( Figure 6).…”

Strigolactones as mediators of plant growth responses to environmental conditions

“…Mashiguchi and co-workers found that light-signaling-related genes are induced in Arabidopsis seedlings shortly (90 min) following exposure to GR24. 48 Analysis of roots and shoots of WT tomato plants and of the SLs-deficient tomato mutant Sl-ORT1 49,50 suggested that SLs are positive regulators of plant light harvesting. This was deduced from the list of genes induced by GR24, following 24 to 48 h of GR24 treatment, which was enriched in genes putatively associated with light harvesting.…”

Differences in Branch Formation in Indeterminate and Determinate Tomato Types

“…Furthermore, auxin concentrations in apical organs including the terminal flower bud might be related to branching habit in tomato plants. Dun et al (2012), Koltai et al (2010), Leyser (2009), Ongaro and Leyser (2008), and Tucker (1976) reported that the actions of auxin, cytokinin, and strigolactone interact during the growth of axillary buds in Arabidopsis, pea, and tomato. Further study regarding fluctuations in plant growth regulator concentrations including auxin is needed to clarify the differences between these two branching types in tomato.…”