WAP1, a Wheat APETALA1 Homolog, Plays a Central Role in the Phase Transition from Vegetative to Reproductive Growth

Abstract

Heading time in bread wheat (Triticum aestivum L.) is determined by three characters: vernalization requirement, photoperiodic sensitivity and narrow-sense earliness, which are involved in the phase transition from vegetative to reproductive growth. We identified and characterized the APETALA1 (AP1)-like MADS box gene in wheat (WAP1) as an activator of phase transition. Its expression starts just before the phase transition and is maintained during the reproductive phase. Inhibition of WAP1 expression in the transgenic plants by co-suppression affected neither vernalization requirement nor photoperiodic sensitivity, but resulted in delayed narrow-sense earliness, indicating that WAP1 accelerates autonomous phase transition. Analyses of the WAP1 expression in the near-isogenic lines (NILs) for spring habit genes (Vrn) revealed that WAP1 transcripts were induced by vernalization strongly in the NILs with Vrn dominant alleles and weakly with the recessive alleles. Furthermore, WAP1 expression was up-regulated by a long photoperiod in both NILs with and those without a photoperiod-insensitive gene (Ppd). These results suggest that WAP1 is a key gene in the regulatory pathway controlling the phase transition from vegetative to reproductive growth in wheat.

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

“…The VERNALIZATION1 gene (VRN1) encodes a MADS box transcription factor that is a central regulator of vernalizationinduced flowering in cereals [3][4][5][6] . VRN1 is expressed at low levels before vernalization and this limits the rate of progression towards flowering [3][4][5][6] .…”

“…VRN1 is expressed at low levels before vernalization and this limits the rate of progression towards flowering [3][4][5][6] . Prolonged exposure to low temperatures induces the transcription of VRN1 (refs [3][4][5][6].…”

“…VRN1 is expressed at low levels before vernalization and this limits the rate of progression towards flowering [3][4][5][6] . 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] .…”

“…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 .…”

“…Some alleles of VRN1 are actively expressed without prior cold treatment [3][4][5][6] . These alleles have mutations in the proximal promoter or deletions/insertions in the first intron of VRN1, regions that appear to be required to maintain low levels of VRN1 transcription before vernalization 5,13 .…”