Low infection of Phelipanche aegyptiaca in Micro-Tom mutants deficient in CAROTENOID CLEAVAGE DIOXYGENASE 8

Abstract

Strigolactones (SLs), a group of plant hormones, induce germination of root-parasitic plants and inhibit shoot branching in many plants. Shoot branching is an important trait that affects the number and quality of flowers and fruits. Root-parasitic plants such as Phelipanche spp. infect tomato roots and cause economic damage in Europe and North Africa. Thus, resistant tomato cultivars are needed. In this study, we found carotenoid cleavage dioxygenase 8-defective mutants of Micro-Tom tomato (slccd8) by the "targeting induced local lesions in genomes" (TILLING) method. The mutants showed excess branching, which was suppressed by exogenously applied SL. Grafting shoot scions of the slccd8 mutants onto wild-type (WT) rootstocks restored normal branching in the scions. The levels of endogenous orobanchol and solanacol in WT were enough detectable, whereas that in the slccd8 mutants were below the detection limit of quantification analysis. Accordingly, root exudates of the slccd8 mutants hardly stimulated seed germination of root parasitic plants. In addition, SL deficiency did not critically affect the fruit traits of Micro-Tom. Using a rhizotron system, we also found that Phelipanche aegyptiaca infection was lower in the slccd8 mutants than in wild-type Micro-Tom because of the low germination. We propose that the slccd8 mutants might be useful as new tomato lines resistant to P. aegyptiaca.

Direct conversion of carlactonoic acid to orobanchol by cytochrome P450 CYP722C in strigolactone biosynthesis

“…SlCYP722C-KO plants did not show the prominent phenotypes of the SL-deficient mutant Slccd8, such as increased shoot branching and reduced stem length (Fig. 6, B to D) (23). Methyl carlactonoate (MeCLA) is known to potentially function as an active hormone that inhibits shoot branching in Arabidopsis (14); however, MeCLA was undetectable in root exudates and root and shoot extracts in SlCYP722C-KO plants, and it was unclear whether MeCLA contributes to the regulation of plant architecture in SlCYP722C-KO plants ( fig.…”

“…Moreover, CYP722C-KO plants have the potential to combat noxious root parasitic weeds. SlCYP722C-KO plants reduce the germination of P. aegyptiaca, a serious constraint on tomato production (23,24), without changing the plant architecture, and they release CLA from the roots. The activity of CLA against the hyphal branching of AMF was comparable with that of natural canonical SLs such as strigol and sorgomol (25), suggesting that CLA can be used as a signaling molecule to facilitate symbiotic interactions with AMF.…”

“…Error bars represent means ± SE (n = 3 biologically independent plants). (B to D) Comparisons of shoot branching (C) and stem length (D) between WT, SlCYP722C-KO, and SL-deficient mutant Slccd8 (line 2757)(23). Red arrows indicate outgrowing axillary buds (>2 mm).…”

Bi‐directional, long‐distance hormonal signalling between roots and shoots of soil water availability

“…Grafting experiments in pea (Beveridge et al, 2000) and tomato (Hasegawa et al, 2018) showed that root‐synthesised SLs could phenotypically revert the branching phenotype of SL‐deficient shoots, indicating acropetal SL transport from the root. Unlike ABA, SL transport is unidirectional with no evidence of basipetal transport of SL from the shoot to the root (Kameoka & Kyozuka, 2018).…”