Plant hormones regulate inducible asexual reproduction in Kalanchoë pinnata

Abstract Many Kalanchoë species reproduce asexually by forming plantlets in the leaf margins. Plant hormones are involved in meristem and embryogenesis pathways, yet the exact role of hormones in Kalanchoë plantlet formation is elusive. Here, we show that auxin and cytokinin-mediated pathways facilitate the establishment of leaf crenulations and, in turn, plantlet primordia in Kalanchoë pinnata. Antisense transgenic lines with lower expression of the auxin transporter, K. pinnata PIN-FORMED1 (KpPIN1) and the cytokinin signalling inhibitor, K. pinnata ARABIDOPSIS HISTIDINE-CONTAINING PHOSPHOTRANSFER PROTEIN (KpAHP), generated fewer plantlets. GREEN FLUORESCENT PROTEIN (GFP) reporter lines visualising the activity of auxin and cytokinin also revealed the accumulation of these hormones in the plantlet primordia. Furthermore, gibberellic acid (GA3) in the leaves prevents plantlet emergence, suggesting that its depletion activates plantlet formation in detached leaves. Our findings emphasise the implication of hormonal regulation in the inducible plantlet formation system, which facilitates the formation of plantlet primordia and exerts precise control over dormancy processes in detached leaves. This work provides insight into the role of hormones in the novel reproductive system in the genus Kalanchoë.