Evolution ofCONSTANSRegulation and Function after Gene Duplication Produced a Photoperiodic Flowering Switch in the Brassicaceae

Abstract

Environmental control of flowering allows plant reproduction to occur under optimal conditions and facilitates adaptation to different locations. At high latitude, flowering of many plants is controlled by seasonal changes in day length. The photoperiodic flowering pathway confers this response in the Brassicaceae, which colonized temperate latitudes after divergence from the Cleomaceae, their subtropical sister family. The CONSTANS (CO) transcription factor of Arabidopsis thaliana, a member of the Brassicaceae, is central to the photoperiodic flowering response and shows characteristic patterns of transcription required for day-length sensing. CO is believed to be widely conserved among flowering plants; however, we show that it arose after gene duplication at the root of the Brassicaceae followed by divergence of transcriptional regulation and protein function. CO has two close homologs, CONSTANS-LIKE1 (COL1) and COL2, which are related to CO by tandem duplication and whole-genome duplication, respectively. The single CO homolog present in the Cleomaceae shows transcriptional and functional features similar to those of COL1 and COL2, suggesting that these were ancestral. We detect cis-regulatory and codon changes characteristic of CO and use transgenic assays to demonstrate their significance in the day-length-dependent activation of the CO target gene FLOWERING LOCUS T. Thus, the function of CO as a potent photoperiodic flowering switch evolved in the Brassicaceae after gene duplication. The origin of CO may have contributed to the range expansion of the Brassicaceae and suggests that in other families CO genes involved in photoperiodic flowering arose by convergent evolution.

Transcriptional and Post-transcriptional Mechanisms Limit Heading Date 1 (Hd1) Function to Adapt Rice to High Latitudes

“…Simon et al, proposed that a CO function has evolved in the Brassicaceae family only after the most recent genome duplication that occurred within the family and that is not shared by its sister family [33]. Evolution of such function created a flexible switch to trigger flowering under LD.…”

“…Comparisons between rice and Arabidopsis can help to derive and test hypotheses concerning protein function, albeit these two species diverged ~150M years ago and the extent of conservation of the Hd1 - Hd3a / CO - FT modules is debated [32,33]. In Arabidopsis, CO can interact with several AtNF-YB and AtNF-YC subunits [34,35].…”

Developmental Control and Plasticity of Fruit and Seed Dimorphism in Aethionema arabicum

“…Heteromorphism in this lineage has been reported for six species (Solms-Laubach, 1901;Hedge, 1965), including Aethionema arabicum, a small diploid, annual, herbaceous plant whose genome sequence was published recently (Haudry et al, 2013). Analysis of the genome has shown that the genus Aethionema shares the ancient whole-genome duplication "At-alpha" with the crown-group Brassicaceae (Schranz et al, 2012); thus, it has been used for comparative molecular evolutionary analyses for several gene families (Hofberger et al, 2015;Mohammadin et al, 2015;Simon et al, 2015). The species has been described as forming two distinct fruit and seed morphs that may influence their propagation strategy (Solms-Laubach, 1901).…”

Editorial: Recent Advances in Flowering Time Control

“…CO -like sequences seem to exist in all plants. Recent evidence indicates that CO of Arabidopsis arose from a family-specific duplication and similar events might have occurred independently in many plant families (Simon et al, 2015). In contrast, plants from the Amaranthaceae family are lacking a true CO ortholog (Dally et al, 2014).…”