Abstract
Safflower (Carthamus tinctorius) is a member of the Asteraceae family that is grown in temperate climates as an oil seed crop. Most commercially grown safflower varieties can be sown in late winter or early spring and flower rapidly in the absence of overwintering. There are winter-hardy safflower accessions that can be sown in autumn and survive over-wintering. Here, we show that a winter-hardy safflower possesses a vernalization response, whereby flowering is accelerated by exposing germinating seeds to prolonged cold. The impact of vernalization was quantitative, such that increasing the duration of cold treatment accelerated flowering to a greater extent, until the response was saturated after 2 weeks exposure to low-temperatures. To investigate the molecular-basis of the vernalization-response in safflower, transcriptome activity was compared and contrasted between vernalized versus non-vernalized plants, in both ‘winter hardy’ and ‘spring’ cultivars. These genome-wide expression analyses identified a small set of transcripts that are both differentially expressed following vernalization and that also have different expression levels in the spring versus winter safflowers. Four of these transcripts were quantitatively induced by vernalization in a winter hardy safflower but show high basal levels in spring safflower. Phylogenetic analyses confidently assigned that the nucleotide sequences of the four differentially expressed transcripts are related to FLOWERING LOCUS T (FT), FRUITFUL (FUL), and two genes within the MADS-like clade genes. Gene models were built for each of these sequences by assembling an improved safflower reference genome using PacBio-based long-read sequencing, covering 85% of the genome, with N50 at 594,000 bp in 3000 contigs. Possible evolutionary relationships between the vernalization response of safflower and those of other plants are discussed.
Highlights
Vernalization is the acceleration of flowering by exposure to the prolonged cold of winter (Chouard, 1960)
There was no significant relationship between cold treatment and flowering time for the spring safflower S317 (p = 0.229, slope coefficient −0.070, R2 0.095)
Temperatures between 0◦C and 12◦C degrees were effective for vernalization of safflower, treatment with 16◦C was less effective for hastening heading date
Summary
Vernalization is the acceleration of flowering by exposure to the prolonged cold of winter (Chouard, 1960). The vernalization response of Arabidopsis is mediated by the FLOWERING LOCUS C (FLC) gene, which encodes a MADS (MCM1/AGAMOUS/DEFICIENS/SRF) box transcription factor protein (Michaels and Amasino, 1999; Sheldon et al, 1999). FLC delays flowering before winter by repressing transcription of genes that would otherwise promote flowering, including FLOWERING LOCUS T (FT), which accelerates flowering in long days (Michaels et al, 2005; Helliwell et al, 2006). Plants retain a molecular memory of winter and flower rapidly when exposed to normal growth temperatures and long days after vernalization. FLC-like genes mediate vernalization-induced flowering in other Brassicaceae, including oilseed rape (Tadege et al, 2001; Irwin et al, 2016; O’Neill et al, 2019; Tudor et al, 2020; Yin et al, 2020). The molecular basis of vernalization has been resolved to varying extents in plants outside the Brassicaceae
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
