Efficient and reproducible somatic embryogenesis and micropropagation in tomato via novel structures - Rhizoid Tubers

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.

The multipotent thidiazuron: A mechanistic overview of its roles in callogenesis and other plant cultures in vitro

Thidiazuron (TDZ) is an active substituted phenyl urea compound that has found a significant role as a plant growth regulator. The most exciting aspect of its function is that it can mimic auxins and cytokinin but is chemically different from these two. Many theories have been put forward, and experiments performed to understand the mode of action of TDZ in callogenesis. One suggested mechanism presents that it works by inhibiting the cytokinin degrading enzymes that compete with cytokinin for an active site on the enzyme. An example is the TDZ-induced suppressed expression of gibberellic acid (GA) biosynthesis genes encoding GA3 and GA20 oxidases. This is entailed with a slightly increased expression of GA catabolism genes encoding GA20 oxidase. Similarly, one of the recommendations is that TDZ induces the expression of specific genes and transcription regulatory sequences that are either responsible directly for callus formation or in turn induce other auxins or cytokinin for callogenesis. There is no concise review available that discusses the details of TDZ-induced callus, specifically and other in vitro cultures in general. This review is an attempt to explore all these pathways and mechanisms involved in callogenesis in plants stimulated by TDZ.

Genetic transformation of common beans (Phaseolus vulgaris L.) through Agrobacterium tumefaciens carrying Cry1Ab gene

BACKGROUND

Seed beetles are one of the most important causes of yield loss in bean production. It is essential to develop resistant varieties in the fight against these pests. Agrobacterium-based gene transformation is the most widely used breeding method worldwide to develop insect-resistant varieties.

METHODS AND RESULTS

Embryonic axes and plumule explants were obtained from Agrobacterium tumefciens treated mature zygotic embryos of low and high raw protein-based common bean cultivars Akman 98 and Karacaşehir 90. Agrobacterium tumefaciens contained a synthetic Bacillus thuringiensis insecticidal crystal protein gene (Bt Cry1Ab) controlled by the 35S promoter and NOS terminator sequences. The transformation event was genotype and explant dependent. The plumule explants could not withstand kanamycin-based selection pressure and died. It was possible to get two transgenic plants using embryonic axis explants of low protein cultivar Akman 98. These results were validated using GUS analysis, PCR, RT-PCR, bioassay analysis, and ELISA test from the samples taken from T₀ and T₁ generations. Bioassay tests showed that these plants were protected from the damage of legume seed insects (Bruchus spp.).

CONCLUSIONS

The results are very encouraging and may help in producing better transgenic common bean germplasm leading to safe agriculture and reducing environmental pollutions.

Highly efficient Agrobacterium-mediated transformation and plant regeneration system for genome engineering in tomato

Tomato (Solanum lycopersicum L.) is an important vegetable and nutritious crop plant worldwide. They are rich sources of several indispensable compounds such as lycopene, minerals, vitamins, carotenoids, essential amino acids, and bioactive polyphenols. Plant regeneration and Agrobacterium-mediated genetic transformation system from different explants in various genotypes of tomato are necessary for genetic improvement. Among diverse plant growth regulator (PGR) combinations and concentrations tested, Zeatin (ZEA) at 2.0 mg l-1 in combination with 0.1 mg l-1 indole-3-acetic acid (IAA) generated the most shoots/explant from the cotyledon of Arka Vikas (36.48 shoots/explant) and PED (24.68 shoots/explant), respectively. The hypocotyl explant produced 28.76 shoots/explant in Arka Vikas and 19.44 shoots/explant in PED. In contrast, leaf explant induced 23.54 shoots/explant in Arka Vikas and 17.64 shoots/explant in PED. The obtained multiple shoot buds from three explant types were elongated on a medium fortified with Gibberellic acid (GA3) (1.0 mg l-1), IAA (0.5 mg l-1), and ZEA (0.5 mg l-1) in both the cultivars. The rooting was observed on a medium amended with 0.5 mg l-1 indole 3-butyric acid (IBA). The transformation efficiency was significantly improved by optimizing the pre-culture of explants, co-cultivation duration, bacterial density and infection time, and acetosyringone concentration. The presence of transgenes in the plant genome was validated using different methods like histochemical GUS assay, Polymerase Chain Reaction (PCR), and Southern blotting. The transformation efficiency was 42.8% in PED and 64.6% in Arka Vikas. A highly repeatable plant regeneration protocol was established by manipulating various plant growth regulators (PGRs) in two tomato cultivars (Arka Vikas and PED). The Agrobacterium-mediated transformation method was optimized using different explants like cotyledon, hypocotyl, and leaf of two tomato genotypes. The present study could be favourable to transferring desirable traits and precise genome editing techniques to develop superior tomato genotypes.

Adventitious Shoot Regeneration from Leaf Explants in Sinningia Hybrida 'Isa's Murmur'

As a valuable ornamental plant, Sinningia hybrida 'Isa's Murmur' (S. hybrida) has genetic flower diversity, which has great potential to develop different flower characters in the horticultural market. The present study focuses on establishing a practical approach for the sustainable propagation of S. hybrida. Compared with aseptic seeding leaves explants, field-grown leaves explants are more suitable for adventitious shoot regeneration. Adding 0.1 mg L-1 NAA and 2.0 mg L-1 TDZ could obtain the highest adventitious shoot proliferation coefficient (24.5), and the induction rate was 91.7%. The shoot proliferation coefficient (20.7) and the greatest shoot length and induction rate (95.3%) were achieved in 0.1 mg L-1 NAA and 2.0 mg L-1 BA medium, accompanied by rooting formation. Adding 0.5 mg L-1 GA3, 1.0 mg L-1 BA, and 0.2 mg L-1 IBA to MS medium can effectively prolong the regenerated buds for rooting. The best for rooting was 1/2 MS medium containing 0.3 mg L-1 IBA, with the maximum number of roots (13.4 per shoot) and survival rate for transplanting (100%). This work aims to build an efficient, definitive, and scalable protocol for S. hybrida regeneration useful for large-scale cultivation and even more protoplast fusion and genetic transformation to develop more colorful or fragrant flowers.

Piriformospora indica recruits host-derived putrescine for growth promotion in plants

Growth promotion induced by the endosymbiont Piriformospora indica has been observed in various plants; however, except growth phytohormones, specific functional metabolites involved in P. indica-mediated growth promotion are unknown. Here, we used a gas chromatography-mass spectrometry-based untargeted metabolite analysis to identify tomato (Solanum lycopersicum) metabolites whose levels were altered during P. indica-mediated growth promotion. Metabolomic multivariate analysis revealed several primary metabolites with altered levels, with putrescine (Put) induced most significantly in roots during the interaction. Further, our results indicated that P. indica modulates the arginine decarboxylase (ADC)-mediated Put biosynthesis pathway via induction of SlADC1 in tomato. Piriformospora indica did not promote growth in Sladc1-(virus-induced gene silencing of SlADC1) lines of tomato and showed less colonization. Furthermore, using LC-MS/MS we showed that Put promoted growth by elevation of auxin (indole-3-acetic acid) and gibberellin (GA4 and GA7) levels in tomato. In Arabidopsis (Arabidopsis thaliana) adc knockout mutants, P. indica colonization also decreased and showed no plant growth promotion, and this response was rescued upon exogenous application of Put. Put is also important for hyphal growth of P. indica, indicating that it is co-adapted by both host and microbe. Taken together, we conclude that Put is an essential metabolite and its biosynthesis in plants is crucial for P. indica-mediated plant growth promotion and fungal growth.

A Novel and Efficient In Vitro Organogenesis Approach for Ajuga lupulina Maxim

This work was aimed at establishing an effective approach for in vitro propagation of Ajuga lupulina Maxim, a medicinal and ornamental plant mainly found in eastern Xizang, in the western Sichuan region of China. We report an optimum response in the proliferation of axillary shoots from nodal segment explants (10.2 shoots/explant) on MS medium containing 3.0 mg L⁻¹ of 6-benzyladenine (BA). When BA and TDZ individually or in combination with NAA were employed for adventitious shoot regeneration, shoots and embryo-like structures (ELSs) were noted in the callus from leaf explants. The maximum response of 26.4 shoots /explant (81.6%) and 12.0 ELSs/explant were ascertained on MS medium with 4.0 mg L⁻¹ TDZ and 0.1 mg L⁻¹ NAA. The leaf despite browning still demonstrated a high regeneration capacity. TDZ (2.0 mg L⁻¹) and BA (2.0 mg L⁻¹) along with NAA (0.01 mg L⁻¹) were found to perform well for shoot regeneration via callus from shoot tip explants. The best for rooting was MS medium (half-strength) containing indole-3-butyric acid (IBA: 1.5 mg L⁻¹) and (NAA: 0.5 mg L⁻¹) with the maximum number of roots (25.8 per shoot) and the highest rooting frequency (81.71%). The survival of the plantlets in the greenhouse was 78.2% indicative of successful acclimatization. This work is the first report of a consistent, definitive, and unique protocol for A. lupulina regeneration, paving the way for the in vitro preservation of such significant genetic resources and also further allied systems based on such callus-based or embryo-based approaches.

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.

Mass propagation through direct and indirect organogenesis in three species of genus Zephyranthes and ploidy assessment of regenerants through flow cytometry

Genus Zephyranthes consists of economically important plant species due to their high ornamental value and presence of valuable bioactive compounds. However, this genus propagates by asexual division only which gives slow propagation rate. Plant tissue culture has the potential to provide efficient techniques for rapid multiplication and genetic improvement of the genus. In this work, a dual in vitro regeneration system through callus mediated shoot regeneration and direct shoot regeneration in species Zephyranthes candida, Zephyranthes grandiflora and Zephyranthes citrina was investigated. Bulb, leaf and root explants were cultured on Murashige and Skoog (MS) medium amended with different plant growth regulators (PGR's) viz. 2,4-dichlorophenoxyacetic acid (2,4-D), 1-Naphthalene acetic acid (NAA), 6-benzyl amino purine (BAP), N-phenyl-N'-1,2,3 -thiadiazol-5-ylurea (TDZ), 6-Furfuryl- aminopurine (KIN) alone or in combinations for callus induction and regeneration. Only bulb explants showed callus induction and regeneration response on different PGR combinations with a varied response in callus induction percentage, callus color and callus texture. Creamish compact callus (CC) was induced on 2 mg L[Formula: see text] 2,4-D, brown friable callus (BF) on 2 mg L[Formula: see text] NAA + 1 mg L[Formula: see text] BAP and green friable callus (GF) callus on 1 mg L[Formula: see text] KIN + 3 mg L[Formula: see text] NAA. The maximum shoot multiplication from different callus types (indirect organogenesis) was achieved on 2 mg L[Formula: see text] BAP alone without combinations. Bulb explants of Z. grandiflora induced maximum callus induction percentage (86.4%) and shoot regeneration percentage (83.5%) with the maximum 08 shoots per 150 mg callus mass. The induction and regeneration response was followed in the order of Z. grandiflora > Z. candida > Z. citrina. Similarly, maximum direct organogenesis from bulb explants was obtained in Z. grandiflora (93.3%) followed by Z. candida (91.5%) and Z. citrina (90.4%) on 3 mg L[Formula: see text] TDZ amended MS media. Adventitious root induction was achieved on 2 mg L[Formula: see text] IBA with a maximum of 8 roots per shoot. The in vitro raised plantlets were successfully acclimatized in the field with 85% survival efficiency. The genome size (2C DNA content) of the field-grown plants and in vitro regenerated plants, evaluated through flow cytometry technique, were similar and showed no ploidy changes. An efficient mass propagation protocol was established for obtaining plants with unaltered genome size in the three species of Zephyranthes.