Approaching the genetic dissection of indirect adventitious organogenesis process in tomato explants

Optimization of Callus Induction and Shoot Regeneration from Tomato Cotyledon Explants

Cultivated tomato (Solanum lycopersicum L.) is one of the most important horticultural crops in the world. The optimization of culture media for callus formation and tissue regeneration of different tomato genotypes presents numerous biotechnological applications. In this work, we have analyzed the effect of different concentrations of zeatin and indole-3-acetic acid on the regeneration of cotyledon explants in tomato cultivars M82 and Micro-Tom. We evaluated regeneration parameters such as the percentage of callus formation and the area of callus formed, as well as the initiation percentage and the number of adventitious shoots. The best hormone combination produced shoot-like structures after 2-3 weeks. We observed the formation of leaf primordia from these structures after about 3-4 weeks. Upon transferring the regenerating micro-stems to a defined growth medium, it was possible to obtain whole plantlets between 4 and 6 weeks. This hormone combination was applied to other genotypes of S. lycopersicum, including commercial varieties and ancestral tomato varieties. Our method is suitable for obtaining many plantlets of different tomato genotypes from cotyledon explants in a very short time, with direct applications for plant transformation, use of gene editing techniques, and vegetative propagation of elite cultivars.

Effects of Different β-Lactam Antibiotics on Indirect Tomato (Solanum lycopersicum L.) Shoot Organogenesis and Agrobacterium tumefaciens Growth Inhibition In Vitro

A β-lactams that act by inhibiting the bacterial cell wall biosynthesis are one of the most common classes of antibiotics applied to suppress the growth of latent bacterial infection associated with the plant tissue culture, as well as in the Agrobacterium-mediated transformation techniques. Plant sensitivity to antibiotics usually is species-, genotype-, or even tissue-specific and mainly depends on concentrations, growth conditions, and culture system. In the presented article, we estimated a comparative effect of four β-lactam antibiotics (Claforan^®, timentin, amoxicillin, and Amoxiclav^®) at different concentrations in an agar-solidified Murashige and Skoog (MS) culture medium supplemented with 5 mg L^-1 6-benzylaminopurine (6-BA) and 0.1 mg L^-1 indole-3-acetic acid (IAA) on in vitro callus induction and shoot organogenesis from hypocotyl and cotyledon explants of two tomato cultivars (Rekordsmen, Moryana). The role of clavulanic acid in combination with amoxicillin (Amoxiclav^®) in the shoot organogenesis frequency and number of shoots per explant has been demonstrated. Additionally, the growth inhibition of Agrobacterium tumefaciens AGL0 strain according to agar disk-diffusion assay was studied. As a result, both stimulatory (timentin, amoxicillin, and Amoxiclav^®) and inhibitory (Claforan^®) effects of β-lactam antibiotics on in vitro morphogenetic responses of tomato were noted. It was found that clavulanic acid, which is part of the commercial antibiotic Amoxiclav^®, significantly increased the shoot regeneration frequency from cotyledon and hypocotyl explants of Rekordsmen tomato cultivar. Possible reasons for the stimulating effect of clavulanic acid on the induction of shoot organogenesis are discussed. According to agar disk-diffusion assay, the maximum diameter of growth inhibition zones (43.9 mm) was identified using 200 mg L^-1 timentin. The in vitro antibacterial activity of tested β-lactam antibiotics was arranged in the following order: timentin > Claforan^® > amoxicillin ≥ Amoxiclav^®. Thus, to suppress the growth of internal and latent bacterial infection of tomato plant tissue culture, as well as for transformation of Moryana and Rekordsmen cultivars by A. tumefaciens strain AGL0, we recommend adding of 100-200 mg L^-1 timentin or 400-800 mg L^-1 Amoxiclav^® to the shoot induction medium.