The Quest for a Key Gene Controlling Acquisition of Cell Competence During In Vitro Organogenesis in Tomato

Abstract

Plants show a remarkable capacity for vegetative propagation through de novo organogenesis. Unlike their wild relatives, most commercially important crop species lack this ability, which is largely attributed to their inability to acquire regeneration competence by dedifferentiation of somatic cells. In vitro micropropagation relies heavily on overcoming such regeneration recalcitrance for its success in biotechnology and clonal propagation in agriculture. Here, we investigate a key locus (Regeneration1) responsible for acquisition of competence that confers high rates of de novo shoot and root organogenesis in tomato. In vitro shoot regeneration assay was performed in several Solanum pennellii introgression lines into S. lycopersicum cv. Micro-Tom (MT) to help identify 29 candidate RG1 genes from a genomic region that originally occupied 6.16 Mbps with 293 genes. We used recalcitrant genotype MT as well as the highly regenerant S. pennellii and its introgression line MT-Rg3C in a subsequent in vitro shoot regeneration assay to characterize the expression of candidate genes using RT-qPCR. Two candidate genes were upregulated in both S. pennellii and MT-Rg3C in comparison to MT. Since the dominant recalcitrance trait may be conferred by mutations leading to lack of function in MT, sequence variations of the 29 candidates were compared between the S. pennellii and MT genomes. Ten genes were identified with mutations that may cause loss of function. Furthermore, 11 novel proteins with unknown functions were identified with polymorphisms for further investigation. Here we propose at least 10 candidate genes for functional characterization in other highly regenerant genotypes to ultimately end the quest for a key gene controlling organogenesis in tomato.