Genetic Transformation of Micro-Tom Tomato with a Citrus Calcium Signal Modifier Gene (CSM-1)

Candidatus Liberibacter (Ca. L.) spp. infects citrus and several members of the Solanaceae family, including tomatoes and causes reduction of productivity. In citrus, Ca. liberibacter asiaticus, causal agent of citrus greening or HLB, has been devastating the Florida citrus industry and the bacterium is already spread to several states. Ca. L. solanacearum (Lso) infects tomatoes, potatoes and other solanaceous crops. Transgenic citrus plants transformed with a calcium signal modifier (CSM-1) gene showed resistance to a bacterial and two fungal pathogens in preliminary detached leaf assays and are going to be tested for resistance to HLB. Citrus has a long juvenile period, and any unintended consequences of the overexpression of a gene will take long time to be detected. A tomato variety called Micro-Tom (MT) was used in this research as model organism to evaluate the expression of CSM-1 gene, in attempt to determine if this gene, without being codon optimized for tomato, would deliver any resistance to Lso bacterium and to evaluate any possible “side effects” of CSM-1 expression. Agrobacterium-mediate- genetic transformation was performed and 18 transgenic lines were produced and expression of CSM-1 gene was verified by RT-PCR. Some transgenic MT lines produced seedless fruit; other lines produced low to moderate seeds giving a mean of 2.12 seeds per fruit and a 60% germination rate. Pollen viability was determined by germination on semi-solid medium for seedless lines and observed every 3h. Wild type MT pollen germination was 37.94% while it was 2.19% in one of the transgenic lines. Offspring of transgenic MT tomato plants were infected with Lso via tomato/potato psyllid (Bactericera cockerelli) feeding and infected plants were confirmed by quantitative PCR (qPCR). CSM-1 gene copy number was determined through qPCR and verified by Southern blots for shoots excised from transgenic calli (T0 plants). Additional information will be presented.