Project description:Perennial plants maintain their life span through several growth seasons. Arabis alpina serves as model Brassicaceae species to study perennial traits. A. alpina lateral stems have a proximal vegetative zone with a dormant bud zone, and a distal senescing seed-producing inflorescence zone. We addressed the questions of how this zonation is distinguished at the anatomical level, whether it is related to nutrient storage, and which signals affect the zonation. We found that the vegetative zone ehxibits secondary growth, which we termed the perennial growth zone (PZ). High-molecular weight carbon compounds accumulate there in cambium and cambium derivatives. Neither vernalization nor flowering were requirements for secondary growth and sequestration of storage compounds. The inflorescence zone with only primary growth, termed annual growth zone (AZ), or roots exhibited different storage characteristics. Following cytokinin application, cambium activity was enhanced and secondary phloem parenchyma was formed in the PZ and also in the AZ. In transcriptome analysis cytokinin-related genes represented enriched gene ontology terms and were expressed at higher level in PZ than AZ. Thus, A. alpina uses primarily the vegetative PZ for nutrient storage, coupled to cytokinin-promoted secondary growth. This finding lays a foundation for future studies addressing signals for perennial growth.
Project description:Flowering of perennial Arabis alpina, is differentially regulated on primary and axillary shoots. Although contributions of vernalization and aging pathways have been analyzed, those of photoperiodic flowering genes CONSTANS (CO), FLOWERING LOCUS T (FT), and TWIN-SISTER OF FT (TSF) remain unexplored. CRISPR-Cas9 mutations in AaCO and AaFT/TWIN SISTER OF FT-LIKE (TSFL) were recovered. Aaco and Aaft/tsfl mutants in pep1 background were scored for flowering time, inflorescence branching and floral phenotypes under long (LD) or short days (SD) and after vernalization. RNAseq data on primary and axillary branches were compared. AaCO activates AaFT/TSFL transcription in leaves, and Aaco and Aaft tsfl mutations delay flowering under LDs. Axillary branches flowered in Aaco mutants but not in Aaft tsfl mutants. Both lacked inflorescence branches and flowers on the primary shoot under LDs. However, Aaft tsfl mutants produced some flowers after vernalization, and Aaco a few in SDs. RNAseq identified genes responsive to AaFT, TSFL and AaCO on the primary shoot and in axillary branches. Therefore, AaCO-AaFT promote flowering of A. alpina under LDs, but with distinct roles in axillary branch flowering. Both genes are required for inflorescence branching and flower formation on the primary shoot. The complex role of the CO-FT module in inflorescence architecture may underlie the polycarpic, perennial life history of A. alpina.
Project description:Arctic alpine species experience extended periods of cold and unpredictable conditions during flowering. Thus, often, alpine plants use both sexual and asexual means of reproduction to maximise fitness and ensure reproductive success. We used the arctic alpine perennial Arabis alpina to explore the role of prolonged cold exposure on adventitious rooting. We exposed plants to 4 °C for different durations and scored the presence of adventitious roots on the main stem and axillary branches. Our physiological studies demonstrated the presence of adventitious roots after 21 weeks at 4 °C saturating the effect of cold on this process. Notably, adventitious roots on the main stem developingin specific internodes allowed us to identify the gene regulatory network involved in the formation of adventitious roots in cold using transcriptomics. These data and histological studies indicated that adventitious roots in A. alpina stems initiate during cold exposure and emerge after plants experience growth promoting conditions. While the initiation of adventitious root was not associated with changes of DR5 auxin response and free endogenous auxin level in the stems, the emergence of the adventitious root primordia was. Using the transcriptomic data, we discerned the sequential hormone responses occurring in various stages of adventitious root formation and identified supplementary pathways putatively involved in adventitious root emergence, such as glucosinolate metabolism. Together, our results highlight the role of low temperature during clonal growth in alpine plants and provide insights on the molecular mechanisms involved at distinct stages of adventitious rooting.
Project description: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.