PERPETUAL FLOWERING2 coordinates the vernalization response and perennial flowering in Arabis alpina.

Ana Lazaro,Kashif Nawaz,Yanhao Zhou,George Coupland,Ales Pecinka,Miriam Giesguth,Sara Bergonzi,Maria C Albani

doi:10.1093/jxb/ery423

Abstract

The floral repressor APETALA2 (AP2) in Arabidopsis regulates flowering through the age pathway. The AP2 ortholog in the alpine perennial Arabis alpina, PERPETUAL FLOWERING 2 (PEP2), was previously reported to control flowering through the vernalization pathway via enhancing the expression of another floral repressor PERPETUAL FLOWERING 1 (PEP1), the ortholog of Arabidopsis FLOWERING LOCUS C (FLC). However, PEP2 also regulates flowering independently of PEP1. To characterize the function of PEP2, we analyzed the transcriptomes of pep2 and pep1 mutants. The majority of differentially expressed genes were detected between pep2 and the wild type or between pep2 and pep1, highlighting the importance of the PEP2 role that is independent of PEP1. Here, we demonstrate that PEP2 activity prevents the up-regulation of the A. alpina floral meristem identity genes FRUITFUL (AaFUL), LEAFY (AaLFY), and APETALA1 (AaAP1), ensuring floral commitment during vernalization. Young pep2 seedlings respond to vernalization, suggesting that PEP2 regulates the age-dependent response to vernalization independently of PEP1. The major role of PEP2 through the PEP1-dependent pathway takes place after vernalization, when it facilitates PEP1 activation both in the main shoot apex and in axillary branches. These multiple roles of PEP2 in the vernalization response contribute to the A. alpina life cycle.

Highlights

Plant adaptation to the environment requires the modification of developmental traits, among which flowering time is key to ensure successful production of offspring
Only 47 genes were up-regulated and 98 genes were downregulated in pep1-1 compared with the wild type (Fig. 1A, B; Supplementary Dataset S2).The genes differentially expressed between pep1-1 and the wild type are influenced by PERPETUAL FLOWERING 1 (PEP1), whereas those differentially expressed between pep2-1 and the wild type are affected by PERPETUAL FLOWERING 2 (PEP2) through both the PEP1dependent and PEP1-independent pathway
Gene Ontology (GO) analysis demonstrated that the most enriched category for the up-regulated genes in pep2-1 compared with the wild type and in pep2-1 compared with pep1-1 was the biosynthesis of glucosinolates, which are involved in defense against herbivore attack and pathogens (Supplementary Fig. S1) (Keith and Mitchell-Olds, 2017)

Summary

Introduction

Plant adaptation to the environment requires the modification of developmental traits, among which flowering time is key to ensure successful production of offspring. Alpine habitats in which juvenile survival is very low are mainly dominated by perennial species (Billings and Mooney, 1968). The perennial growth habit relies on the differential behavior of meristems on the same plant so that some will stay vegetative whereas others will initiate flowering (Amasino, 2009; Lazaro et al, 2018).The main environmental cue that promotes flowering in alpine species is the exposure to prolonged cold, a process called vernalization. Alpine environments are characterized by short growing seasons and long periods of snow. This is especially true for perennial species, as most of them have a prolonged juvenile phase and are not competent to flower at a young age (Bergonzi and Albani, 2011)

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Discussion

Conclusion