Sandra Bretones

Key Message The identification of the tomato DOR gene that is essential for adventitious organogenesis provides a genetic target for improving regeneration efficiency and root system performance in tissue culture and plant breeding. Abstract Plant rooting and adventitious organogenesis represent major bottlenecks in the application of plant tissue culture techniques. In this study, we characterize the dor mutant (defective in organogenesis and rooting) identified in our collection of tomato T-DNA lines. This mutant exhibits normal callus proliferation but fails to differentiate adventitious buds. Additionally, it displays underdeveloped embryonic roots, and its adventitious roots derived from various explants are also altered. Grafting experiments revealed compromised in vivo development primarily due to its abnormal root system. Upon identifying an allelic mutant in another tomato line, we observed no co-segregation between a T-DNA insert and the phenotype in either of the identified allelic mutants. Through mapping-by-sequencing, we identified Solyc12g098670 as the gene responsible for this mutation, which is homologous to SIGNAL PEPTIDE PEPTIDASE-LIKE (SPPL) genes from Arabidopsis thaliana, particularly SPPL3 and SPPL5. The expression pattern of DOR in tomato is nearly ubiquitous, similar to SPPL3 in Arabidopsis, yet the regeneration and rooting of sppl3 Arabidopsis mutants resemble the wild-type. In both tomato and Solanum pennellii (Correll) D’Arcy, RNAi lines and plants edited by CRISPR/Cas exhibit a dor mutant phenotype. However, by increasing the expression level of DOR, the plants become indistinguishable from the wild-type in terms of in vitro and in vivo development. Overexpression of this gene in the mutant has enabled the regeneration of plants with a wild-type phenotype. These results demonstrate that DOR is the first member of the tomato SPPL gene family known to be associated with root development and adventitious organogenesis.

Agricultural systems are currently facing significant issues, primarily due to population growth rates in the context of global climate change. Rising temperatures cause plant heat stress and impact crop yield, which in turn compromises global food production and safety. Climate change is also having a significant impact on water availability around the world, and droughts are becoming more frequent and severe in many regions. The combined effect of both heat and drought stresses increases plant damage, resulting in reduced plant development and productivity loss. Therefore, developing heat–drought-tolerant crop varieties is crucial for enhancing yield under these challenging conditions. Tomato (Solanum lycopersicum L.), a major vegetable crop highly appreciated for its nutritional qualities, is particularly sensitive to extreme temperatures, which have a significant negative impact on tomato fruit setting and cause male gametophyte abortion. In this work, a classical genetic approach was employed to identify tomato genotypes showing a resilient response to combined heat and drought stress conditions. A phenotype screening of a natural germplasm collection and an ethyl methanesulfonate (EMS) mutagenized population resulted in the identification of a significant number of tomato lines tolerant to combined heat and drought conditions, specifically 161 EMS lines and 24 natural accessions as tolerant. In addition, TILLING and Eco-TILLING analyses were used as proof-of-concept to isolate new genetic variants of genes previously reported as key regulators of abiotic stress responses in different species. The identification of these variants holds the potential to provide suitable plant material for breeding programs focused on enhancing tomato resilience to adverse climate conditions.

Tomato (Solanum lycopersicum L.) is a major horticultural crop and a model species among eudicots, especially for traits related to reproductive development. Although considerable progress has been made since the tomato genome sequence project was completed, most of the genes identified remain predictions with an unknown or hypothetical function. This lack of functional characterization hampers the use of the huge amount of genomic information available to improve the quality and productivity of this crop. Reverse genetics strategies such as artificial mutagenesis and next-generation sequencing approaches build the perfect tandem for increasing knowledge on functional annotation of tomato genes. This work reports the phenotypic characterization of a tomato mutant collection generated from an EMS chemical mutagenesis program aimed to identify interesting agronomic mutants and novel gene functions. Tomato mutants were grouped into fourteen phenotypic classes, including vegetative and reproductive development traits, and the inheritance pattern of the identified mutations was studied. In addition, causal mutation of a selected mutant line was isolated through a mapping-by-sequencing approach as a proof of concept of this strategy’s successful implementation. Results support tomato mutagenesis as an essential tool for functional genomics in this fleshy-fruited model species and a highly valuable resource for future breeding programs of this crop species aimed at the development of more productive and resilient new varieties under challenging climatic and production scenarios.