Expression of Melocactus glaucescens SERK1 sheds new light on the mechanism of areolar activation in cacti

Areolar activation is the most popular in vitro propagation method for cacti. Even though it is relatively simple, few established protocols exist. Acquisition of a competent state has been linked to the expression of SOMATIC EMBRYOGENESIS RECEPTOR KINASE (SERK) during plant organogenesis. Here, cell competence acquisition and areolar activation were investigated during Melocactus glaucescens shoot organogenesis. Degenerate PCR primers and transcriptome data enabled the characterization of MgSERK1, the first known Cactaceae SERK sequence. Phylogenetic analysis based on SERKs from 23 angiosperm species revealed elevated similarity to other SERK Dicot S1/2 sequences and identified the corresponding SERK1 orthologs. Treated explants had the areolar region punctured three times, and shoot organogenesis was induced by exposure to 17.76 µM 6-benzyladenine and 1.34 µM 1-naphthaleneacetic acid. Shoot organogenesis was analyzed by comparing treated and non-treated explants. Anatomical examination and in situ hybridization showed that shoot organogenesis occurred via areolar activation from procambial cells in the stem cortex. Wounding of the areola region activated the axillary bud and increased the number of shoots produced per explant. In situ expression revealed the association of MgSERK1 with M. glaucescens shoot organogenesis in the areola, its adjacent regions, and the roots. This is the first characterization of a SERK1 gene in cacti. Its expression during areolar activation is associated with shoot and root organogenesis in Melocactus glaucescens.