The influence of vernalization and daylength on expression of flowering-time genes in the shoot apex and leaves of barley (Hordeum vulgare).

Abstract

Responses to prolonged low-temperature treatment of imbibed seeds (vernalization) were examined in barley (Hordeum vulgare). These occurred in two phases: the perception of prolonged cold, which occurred gradually at low temperatures, and the acceleration of reproductive development, which occurred after vernalization. Expression of the VERNALIZATION1 gene (HvVRN1) increased gradually in germinating seedlings during vernalization, both at the shoot apex and in the developing leaves. This occurred in darkness, independently of VERNALIZATION2 (HvVRN2), consistent with the hypothesis that expression of HvVRN1 is induced by prolonged cold independently of daylength flowering-response pathways. After vernalization, expression of HvVRN1 was maintained in the shoot apex and leaves. This was associated with accelerated inflorescence initiation and with down-regulation of HvVRN2 in the leaves. The largest determinant of HvVRN1 expression levels in vernalized plants was the length of seed vernalization treatment. Daylength did not influence HvVRN1 expression levels in shoot apices and typically did not affect expression in leaves. In the leaves of plants that had experienced a saturating seed vernalization treatment, expression of HvVRN1 was higher in long days, however. HvFT1 was expressed in the leaves of these plants in long days, which might account for the elevated HvVRN1 expression. Long-day up-regulation of HvVRN1 was not required for inflorescence initiation, but might accelerate subsequent stages of inflorescence development. Similar responses to seed vernalization were also observed in wheat (Triticum aestivum). These data support the hypothesis that VRN1 is induced by cold during winter to promote spring flowering in vernalization-responsive cereals.

Direct links between the vernalization response and other key traits of cereal crops

“…Among the overlap between the two methods of analysis were 321 genes that were upregulated and 78 downregulated by twofold or more (Po0.05, adjusted P value, DEseq or EdgeR). The upregulated genes include a number of genes that potentially promote floral development including VRN1 and VRN1-like genes (Barley MADS 3,8), and also four other MADS box genes including a PANICLE ARCHI-TECTURE2-like gene. In addition, FT1 and FT2 showed elevated transcript levels in the VRN1-HA positive line.…”

“…Prolonged exposure to low temperatures induces the transcription of VRN1 (refs [3][4][5][6]. Induction of VRN1 begins rapidly with the onset of cold but the initial expression is low and several weeks at low temperatures are required for VRN1 transcripts to accumulate to a level that will promote rapid flowering [3][4][5][6][7][8] . After vernalization, VRN1 transcript levels remain elevated in leaves and at the shoot apex 5,8 .…”

“…Induction of VRN1 begins rapidly with the onset of cold but the initial expression is low and several weeks at low temperatures are required for VRN1 transcripts to accumulate to a level that will promote rapid flowering [3][4][5][6][7][8] . After vernalization, VRN1 transcript levels remain elevated in leaves and at the shoot apex 5,8 . The expression of VRN1 at the shoot apex is likely to promote inflorescence meristem identity, whereas the expression of VRN1 in leaves is required for the long-day flowering response [8][9][10][11][12] .…”

“…After vernalization, VRN1 transcript levels remain elevated in leaves and at the shoot apex 5,8 . The expression of VRN1 at the shoot apex is likely to promote inflorescence meristem identity, whereas the expression of VRN1 in leaves is required for the long-day flowering response [8][9][10][11][12] .…”

Evolution of VRN2/Ghd7-Like Genes in Vernalization-Mediated Repression of Grass Flowering

“…The current molecular model of vernalization responsiveness in wheat and barley involves a leaf-specific regulatory loop among VERNALIZATION1 (VRN1), VRN2, and VRN3 Distelfeld et al, 2009a;Greenup et al, 2009;Sasani et al, 2009), the latter of which is homologous to Arabidopsis (Arabidopsis thaliana) FT, which encodes a small protein that moves from leaves to the shoot apical meristem to promote flowering (Yan et al, 2006;Turck et al, 2008). During growth of vernalization-requiring cereals in the fall season, the CONSTANS-like gene VRN2 represses FT to prevent flowering, and the FRUITFULL-like gene VRN1 is transcribed at very low levels (Yan et al, 2004a(Yan et al, , 2006Hemming et al, 2008;Sasani et al, 2009).…”