Natural Variation in the Control of Flowering and Shoot Architecture in Diploid Fragaria Species.

Guangxun Fan,Javier Andrés,Klaus Olbricht,Timo Hytönen,Elli Koskela

doi:10.3389/fpls.2022.832795

Abstract

In perennial fruit and berry crops of the Rosaceae family, flower initiation occurs in late summer or autumn after downregulation of a strong repressor TERMINAL FLOWER1 (TFL1), and flowering and fruiting takes place the following growing season. Rosaceous fruit trees typically form two types of axillary shoots, short flower-bearing shoots called spurs and long shoots that are, respectively, analogous to branch crowns and stolons in strawberry. However, regulation of flowering and shoot architecture differs between species, and environmental and endogenous controlling mechanisms have just started to emerge. In woodland strawberry (Fragaria vesca L.), long days maintain vegetative meristems and promote stolon formation by activating TFL1 and GIBBERELLIN 20-OXIDASE4 (GA20ox4), respectively, while silencing of these factors by short days and cool temperatures induces flowering and branch crown formation. We characterized flowering responses of 14 accessions of seven diploid Fragaria species native to diverse habitats in the northern hemisphere and selected two species with contrasting environmental responses, Fragaria bucharica Losinsk. and Fragaria nilgerrensis Schlecht. ex J. Gay for detailed studies together with Fragaria vesca. Similar to F. vesca, short days at 18°C promoted flowering in F. bucharica, and the species was induced to flower regardless of photoperiod at 11°C after silencing of TFL1. F. nilgerrensis maintained higher TFL1 expression level and likely required cooler temperatures or longer exposure to inductive treatments to flower. We also found that high expression of GA20ox4 was associated with stolon formation in all three species, and its downregulation by short days and cool temperature coincided with branch crown formation in F. vesca and F. nilgerrensis, although the latter did not flower. F. bucharica, in contrast, rarely formed branch crowns, regardless of flowering or GA20ox4 expression level. Our findings highlighted diploid Fragaria species as rich sources of genetic variation controlling flowering and plant architecture, with potential applications in breeding of Rosaceous crops.

Highlights

The Rosaceae family contains economically important perennial crops, ranging from herbaceous species, such as strawberries (Fragaria spp.) to fruit trees like apples (Malus × domestica Borkh.) or peaches [Prunus persica (L.) Batsch; Kurokura et al, 2013]
Opposite photoperiodic response was found in two accessions of F. nilgerrensis, in which short days (SD) resulted in a higher percentage of flowering plants
We provide the first phenotype and gene expression level analyses on the control of flowering and axillary meristem fates in several wild diploid Fragaria species under controlled environmental conditions

Summary

Introduction

The Rosaceae family contains economically important perennial crops, ranging from herbaceous species, such as strawberries (Fragaria spp.) to fruit trees like apples (Malus × domestica Borkh.) or peaches [Prunus persica (L.) Batsch; Kurokura et al, 2013]. In the perennial herbaceous model species F. vesca, floral induction is highly dependent on the interaction of temperature and photoperiod, and natural populations exhibit differences in their responses to these environmental cues. A population sampled from the North of Norway shows a strikingly altered yearly growth cycle with an obligatory requirement for vernalization (Heide and Sønsteby, 2007; Koskela et al, 2017). Given that such variation in environmental responses exists within a single species, it is imaginable that extending these studies to other related diploid strawberry species could reveal further adaptations to local environments. Characterizing the available diversity within the Fragaria genus may prove useful for researchers and for breeders looking for novel breeding targets to improve climatic adaptation of Rosaceous crops

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