Tuning growth cycles of Brassica crops via natural antisense transcripts of BrFLC

Abstract

SummarySeveral oilseed and vegetable crops of Brassica are biennials that require a prolonged winter cold for flowering, a process called vernalization. FLOWERING LOCUS C (FLC) is a central repressor of flowering. Here, we report that the overexpression of natural antisense transcripts (NATs) of Brassica rapa FLC (BrFLC) greatly shortens plant growth cycles. In rapid-, medium-and slowcycling crop types, there are four copies of the BrFLC genes, which show extensive variation in sequences and expression levels. In Bre, a biennial crop type that requires vernalization, five NATs derived from the BrFLC2 locus are rapidly induced under cold conditions, while all four BrFLC genes are gradually down-regulated. The transgenic Bre lines overexpressing a long NAT of BrFLC2 do not require vernalization, resulting in a gradient of shortened growth cycles. Among them, a subset of lines both flower and set seeds as early as Yellow sarson, an annual crop type in which all four BrFLC genes have non-sense mutations and are nonfunctional in flowering repression. Our results demonstrate that the growth cycles of biennial crops of Brassica can be altered by changing the expression levels of BrFLC2 NATs. Thus, BrFLC2 NATs and their transgenic lines are useful for the genetic manipulation of crop growth cycles.

Nucleotide polymorphism affecting FLC expression underpins heading date variation in horticultural brassicas

“…There are therefore parallels between this molecular variation and the natural variation in vernalization response in A. thaliana (Coustham et al ., ). The conservation of COOLAIR (Swiezewski et al ., ), the AtFLC antisense RNA in Arabis alpina (Castaings et al ., ) and in B. rapa (Li et al ., ), also points to strong commonality in the regulation of FLC across the Brassicaceae. Non‐coding sequence polymorphism has recently been shown to define a small number of major AtFLC haplotype groups varying in AtFLC expression and degree of epigenetic silencing (Li et al ., ).…”

Genetic and Epigenetic Regulation of Vernalization in Brassicaceae

“…By contrast, COOLAIR-like transcripts were detected only from BrFLC2, and these transcripts were induced by cold treatment. The plant growth cycle was shortened by the over-expression of FLC natural antisense transcripts (NATs) (COOLAIR-like) resulting in decreased flowering time and FLC expression, suggesting that the activity of the BrFLC2 gene was suppressed by BrFLC NATs during cold condition [88]. BoFLC2 was shown to be a major determinant of heading date variation and vernalization response through allelic variation, and sequence polymorphisms in BoFLC2 alter the sensitivity and silencing dynamics of its expression [73].…”

“…In A. thaliana, it has been revealed that lncRNAs such as COOLAIR, COLDAIR, and COLDWRAP are involved in vernalization [49,54,56]. Currently, COOLAIR-like transcripts were detected only from BrFLC2, and these transcripts were involved in the suppression of BrFLC2 and maybe other BrFLCs [88]. However, in B. rapa, there is no report about the transcripts of COLDAIR or COLDWRAP, and regions sharing sequence similarity to the COLDAIR found in A. thaliana were not detected in the first intron of any of the B. rapa paralogs [69].…”

Differential Expression of Flowering Genes between Rapid- and Slow-Cycling Brassica rapa

“…A genetic-genomics approach revealed that BrFLC2 is a major regulator of flowering time in B. rapa (Wu et al 2012;Xiao et al 2013;2014). Recently, Li et al (2016) reported that early flowering phenotypes of B. rapa is related to be nonfunctional BrFLCs which are truncated form by premature termination, but slow or late flowering types contain functional or intact forms of BrFLC1, BrFLC2, and BrFLC3. In addition, Song et al (2015) found out that expression of only one or some of paralogues is closely related to photoperiodic flowering in B. rapa.…”

“…A genetic-genomics approach revealed that BrFLC2 is a major regulator of flowering time in B. rapa (Xiao et al 2013;2014). Recently, Li et al (2016) reported that mutation in FLC1 and FLC2 leading to production of truncated proteins was associated with shortness of flowering time in B. rapa. In photoperiodic flowering pathway, CONSTAS (CO) induces the day-length specific expression of FT in leaves (Putterill et al 1995;Samach et al 2000).…”