We explore environmental and genetic regulation of growth cycle in a perennial model species woodland strawberry (Fragaria vesca).
Wood­land straw­berry model sys­tem

Woodland strawberry is a small perennial rosette plant. It's an excellent perennial model because of its short life cycle (<4 months from seed to seed) compared to many other perennials, and its abundant runners enable easy production of clones. Woodland strawberry is a simple model for genetic research because it is self-compatible, it has a small diploid genome of ~206Mb, and an efficient genetic transformation method is available. Finally, its broad distribution accross the Europe between latitudes 37-70ºN makes it an excellent model for climate adaptation studies.

Perennial climate adaptation

Association of phenotypic variation with environmental clines is considered as a sign of local adaptation. We use population genomics to study climate adaptation in woodland strawberry that has colonized almost whole Europe after the last glaciation and that exhibits latitudinal phenotypic clines. Using a large plant collection covering latitudinal range of the species in Europe and whole genome resequencing data, we explore population history, signatures of natural selection, and the association of genotypes with phenotypic variation and environmental parameters. Based on these approaches, we try to find genes that contributed to climate adaptation in past, and are thus potential targets for breeding new crop cultivars better adapted to future changing climate. We confirm the function of the most promising candidate regulators using various molecular and physiological analyses.

Genetic control of perennial growth cycle in woodland strawberry

A perpetual flowering mutant of woodland strawberry has been instrumental in the understanding of the perennial growth cycle. We have demonstrated that a mutation in the woodland strawberry homolog of TERMINAL FLOWER1 (FvTFL1) causes continuous flowering in the mutant, whereas the functional allele causes typical seasonal flowering habit. FvTFL1 is a strong floral repressor that is highly expressed in the shoot apical meristem in summer. Flower buds are formed by the apical meristems of leaf rosettes after the down-regulation of FvTFL1 mRNA expression in autumn, and overwintering buds produce flowers and fruits next summer. In the spring, FvTFL1 is highly activated in the meristems of new axillary leaf rosettes which remain vegetative until next autumn. We carry out QTL mapping and genome wide association studies to identify new regulators of perennial growth cycle and characterize their functions.

Integration of photoperiodic and temperature signals

Role of photoperiod as a seasonal cue controlling developmental phase shifts in plants has been extensively studied, but the effect of temperature is less clear. Woodland strawberry, as well as many other perennials, show strong response to ambient temperature. Woodland strawberry exhibits obligatory short-day requirement for flower induction only at a narrow temperature range between 13-20 ºC. At this temperature range, photoperiod shorter than ~14 h is needed to down-regulate FvTFL1 and to induce flowering. At cooler temperatures, FvTFL1 mRNA expression is low allowing flower induction to occur independently of the photoperiod, whereas high temperatures above 20 ºC highly activate FvTFL1 that maintain plants in vegetative stage. In order to understand these temperature responses, we are searching for new genes that are involved in the temparature regulation of FvTFL1.

Early fruit development

In strawberry a commercial fleshy fruit is receptacle, a modified flower part. A true fruit, achene, is a dried up ovary containing a single seed located on the surface of receptacle. In fruit development, plant hormones interact to control and synchronize signals between developing seed and surrounding tissues. Studies in model plants identified several genes regulating auxin and GA metabolism that are related to fruit development. Furthermore, exogenous hormone application can induce parthenocarpic fruits. Likewise in other plants, the hormones play a critical role in fruit development of Fragaria. However, details about their biosynthesis, distribution and activity in fruit tissues are not well understood. The project focuses on understanding the spatial and temporal distribution of hormones and the molecular basis of fruit set and development in F. vesca.