Morphological and Transcriptional Analyses of Regeneration Events in Pepper Plants (Capsicum annuum)Expose Patterns of Shoot Apical Meristem Formation

Plant cells are endowed with a plastic nature that confers them the capacity to regenerate most plant organs or even an entire plant body from somatic cells. Plant tissue culture procedures take advantage of this asset to induce specific morphogenic responses using hormonal treatments. Still many plants, for example, peppers (Capsicum annuum), are considered recalcitrant because they respond poorly to exogenous hormone applications, which strongly limits transformation and genetic manipulations in this species. In this study, we exposed pepper cotyledon and hypocotyl explants to various cytokinins-containing media and characterized the morphological and gene-expression events that took place during adventitious shoot formation. Cellular organization events were observed and led to the formation of small protrusions, which in turn developed and expanded to form abundant rosette-leaf-like organs. Shoot formation was also obtained, although in rarer cases, and promoted the growth of elongated plantlets that at last rooted well. Moreover, gene-expression analyses of pepper cotyledons exposed to cytokinins revealed the induction of shoot morphogenesis-related genes, reflecting the occurrence of events of shoot apical meristem formation. In addition, we identified an increase in the expression of genes related to carbon and primary metabolism, suggesting the need for energy in this process. Here, we developed a protocol for shoot regeneration in pepper and our results provide new insights into adventitious shoot formation in pepper plants.