Abstract
The vernalization gene 2 (VRN2), is a major flowering repressor in temperate cereals that is regulated by low temperature and photoperiod. Here we show that the gene from Triticum aestivum (TaVRN2) is also regulated by salt, heat shock, dehydration, wounding and abscissic acid. Promoter analysis indicates that TaVRN2 regulatory region possesses all the specific responsive elements to these stresses. This suggests pleiotropic effects of TaVRN2 in wheat development and adaptability to the environment. To test if TaVRN2 can act as a flowering repressor in species different from the temperate cereals, the gene was ectopically expressed in the model plant Arabidopsis. Transgenic plants showed no alteration in morphology, but their flowering time was significantly delayed compared to controls plants, indicating that TaVRN2, although having no ortholog in Brassicaceae, can act as a flowering repressor in these species. To identify the possible mechanism by which TaVRN2 gene delays flowering in Arabidopsis, the expression level of several genes involved in flowering time regulation was determined. The analysis indicates that the late flowering of the 35S::TaVRN2 plants was associated with a complex pattern of expression of the major flowering control genes, FCA, FLC, FT, FVE and SOC1. This suggests that heterologous expression of TaVRN2 in Arabidopsis can delay flowering by modulating several floral inductive pathways. Furthermore, transgenic plants showed higher freezing tolerance, likely due to the accumulation of CBF2, CBF3 and the COR genes. Overall, our data suggests that TaVRN2 gene could modulate a common regulator of the two interacting pathways that regulate flowering time and the induction of cold tolerance. The results also demonstrate that TaVRN2 could be used to manipulate flowering time and improve cold tolerance in other species.
Highlights
In temperate regions, low temperature (LT) constitutes a major factor that regulates flowering time and many developmental transitions such as germination, bud dormancy and bursting [1]
7 days old wheat plants were treated as follows: for cold, seedlings were cold treated for one day at 4uC (CA); for heat shock, they were exposed at 40uC for 1 and 3 h; wounding stress was induced by cutting seedlings into 1 cm segments and placing them in water at 20uC for 3 and 14 h; saltstressed plants were obtained by incubating seedlings for 18 h with 300 or 500 mM NaCl; water stress was induced by removing seedlings from vermiculite and leaving them at 20uC without water for different time periods, after which the relative water content (RWC) was evaluated; for ABA treatment, 100 mM ABA in 0.02% (v/v) Tween-20 for 18 h were sprayed on seedlings
A homology search shows that the 621 bp sequence has 99% identity with the A genome of TdVRN2 (AY485979.1) indicating that the 621 bp could be assigned as the copy A of TaVRN2
Summary
Low temperature (LT) constitutes a major factor that regulates flowering time and many developmental transitions such as germination, bud dormancy and bursting [1]. In response to LT-conditions, plants cold acclimate and vernalize to prevent the sensitive floral meristem from freezing damages during the winter by postponing flowering [2]. The ability of plants to switch from vegetative to reproductive phase after a long period of cold, a process known as vernalization [3], allows plants to promote flowering early in the spring. During this cold exposure period, LT-responsive genes CBFs (C-repeat binding factor) and COR (Cold Regulated) are activated, allowing plants to increase their tolerance to cold and survive the winter ([4]). Understanding the genetic/molecular basis of both LTresponsive pathways (cold acclimation and vernalization), can help to better manipulate, the two important agronomical traits flowering and freezing tolerance
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