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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—hence why 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.
Highlights
Shoot branching determines aerial plant architecture, which is controlled by the formation of axillary buds in the axils of leaves and subsequent outgrowth [1]
Shoot branching is an important trait in agriculture and horticulture because it affects the flower numbers, as well as number and quality of fruits and seeds
To evaluate the infection of SL biosynthesis–defective mutants with P. aegyptiaca, we found two CCD8-defective mutant lines, 2757 and 5291, in Micro-Tom tomato by using the “targeting-induced local lesions in genomes” (TILLING) method (Okabe et al 2011)
Summary
Shoot branching determines aerial plant architecture, which is controlled by the formation of axillary buds in the axils of leaves and subsequent outgrowth [1]. Shoot branching is an important trait in agriculture and horticulture because it affects the flower numbers, as well as number and quality of fruits and seeds. It is important to control number of branches in crop production. Whether axillary buds start to grow or remain dormant is governed by environmental and endogenous cues [2]. The main endogenous cues are plant hormones; cytokinin activate axillary bud outgrowth, whereas auxin, which is transported basipetally, inhibits it [3]. Strigolactones (SLs) inhibit axillary bud outgrowth [4,5]. Several types of natural SLs have been found in root exudates of diverse plant species [6]
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