Keep a distance to be different: axillary bud initiating at a distance to the shoot apical meristem are crucial for the perennial life style of Arabis alpina

Purpose: In higher plants, perennialism is achieved through axillary buds and side-shoots that stay vegetative. This work aims to analyze the pattern of axillary bud (AB) formation in the perennial model plant Arabis alpina and to study the role of LATERAL SUPPRESSOR (AaLAS) gene in this process. Methods: This study combines stereomicroscopic analysis with RNA sequencing to monitor how patterns of AB formation and gene expression correlate. The role of AaLAS was studied using an RNAi approach. Results: During vegetative development, ABs initiate at a distance to the SAM, whereas after induction of flowering ABs initiate adjacent to the SAM. Dormant buds are established before onset of vernalization. Transcript profiles of ABs initiated at a distance were different from that of the SAM, whereas transcript patterns of buds initiated in close proximity were similar to the corresponding SAM. Knock-down of AaLAS leads to loss of both dormant buds and vegetative side-shoots, strongly compromising perennial life style. Conclusions: AB formation is regulated differently during vegetative and reproductive development. New meristems that show gene expression profiles different from the SAM are established at a distance to the SAM. AaLAS plays an essential role in perennial life cycle modulating the establishment of dormant buds and vegetative side-shoots. Comparison of very young axillary bud soon after initiation with its corresponding shoot apical meristem harvested at different developmental stages using Illumina HiSeq3000