Flowering Times of Wild Arabidopsis Accessions From Across Norway Correlate With Expression Levels of FT, CO, and FLC Genes.

Hannah Kinmonth-Schultz,Joy K Ward,Takato Imaizumi,Odd Arne Rognli,Anna Lewandowska-Sabat,Siri Fjellheim

doi:10.3389/fpls.2021.747740

Hannah Kinmonth-Schultz, Joy K Ward + Show 4 more

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https://doi.org/10.3389/fpls.2021.747740

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Abstract

Temperate species often require or flower most rapidly in the long daylengths, or photoperiods, experienced in summer or after prolonged periods of cold temperatures, referred to as vernalization. Yet, even within species, plants vary in the degree of responsiveness to these cues. In Arabidopsis thaliana, CONSTANS (CO) and FLOWERING LOCUS C (FLC) genes are key to photoperiod and vernalization perception and antagonistically regulate FLOWERING LOCUS T (FT) to influence the flowering time of the plants. However, it is still an open question as to how these genes vary in their interactions among wild accessions with different flowering behaviors and adapted to different microclimates, yet this knowledge could improve our ability to predict plant responses in variable natural conditions. To assess the relationships among these genes and to flowering time, we exposed 10 winter-annual Arabidopsis accessions from throughout Norway, ranging from early to late flowering, along with two summer-annual accessions to 14 weeks of vernalization and either 8- or 19-h photoperiods to mimic Norwegian climate conditions, then assessed gene expression levels 3-, 5-, and 8-days post vernalization. CO and FLC explained both FT levels and flowering time (days) but not rosette leaf number at flowering. The correlation between FT and flowering time increased over time. Although vernalization suppresses FLC, FLC was high in the late-flowering accessions. Across accessions, FT was expressed only at low FLC levels and did not respond to CO in the late-flowering accessions. We proposed that FT may only be expressed below a threshold value of FLC and demonstrated that these three genes correlated to flowering times across genetically distinct accessions of Arabidopsis.

Highlights

Plants vary both within and across species when it comes to their degree of responsiveness to seasonal changes in daylength and their complete or facultative requirement for prolonged cold exposure before becoming competent to flower
We focused on the long photoperiod as the original seeds were collected well after photoperiods exceeded 16 h and plants from these accessions likely flowered in the wild when days were long (Supplementary Table 1)
The relationships among FLOWERING LOCUS T (FT), FLOWERING LOCUS C (FLC), and CO have been extensively explored such that we have a solid understanding of how flowering is regulated by photoperiod and vernalization in Arabidopsis and this has translated to our understanding in other species (e.g., Brown et al, 2013; Berry and Dean, 2015; Song et al, 2015; Leijten et al, 2018)

Summary

Introduction

Plants vary both within and across species when it comes to their degree of responsiveness to seasonal changes in daylength (photoperiod) and their complete or facultative requirement for prolonged cold exposure (vernalization) before becoming competent to flower. The model Arabidopsis thaliana is a facultative long-day species, which means it flowers most quickly in the long photoperiods during spring and early summer, and can display either a summer- or winter-annual flowering phenotype (e.g., Lee et al, 1993; Gazzani et al, 2003) Those in the former group complete their lifecycle from germination to seed set in a single growing season (spring to summer) and do not require vernalization to flower. While we well-understand the mechanisms governing photoperiod and vernalization response in Arabidopsis, which has translated to our understanding of photoperiod and vernalization response both in Brassicaceae and other species (e.g., Brown et al, 2013; Berry and Dean, 2015; Song et al, 2015; Leijten et al, 2018), we do not yet fully understand the mechanisms governing both intraand interspecific variation in photoperiod and vernalization responses Such knowledge is necessary if we are to predict plant responses in dynamic, and changing, natural conditions

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