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Published on March 21, 2008; 10.1104/pp.108.116418

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Received January 17, 2008
Accepted March 13, 2008

Low temperature and daylength cues are integrated to regulate FLOWERING LOCUS T in barley

Megan N. Hemming , W. James Peacock , Elizabeth S. Dennis , and Ben Trevaskis *

Commonwealth Scientific and Industrial Research Organisation, Division of Plant Industry, GPO Box 1600, Canberra ACT 2601, Australia

* Corresponding author; email: ben.trevaskis{at}csiro.au.

Interactions between flowering time genes were examined in a doubled haploid barley (Hordeum vulgare) population segregating for VERNALIZATION1 (HvVRN1), VERNALIZATION2 (HvVRN2) and PHOTOPERIOD1 (PPD-H1). A deletion allele of HvVRN2 was associated with rapid inflorescence initiation and early flowering, but only in lines with an active allele of PPD-H1. In these lines, the floral promoter FLOWERING LOCUS T (HvFT1) was expressed at high levels without vernalization, and this preceded induction of HvVRN1. Lines with the deletion allele of HvVRN2 and the inactive ppd-H1 allele did not undergo rapid inflorescence initiation and were late flowering. These data suggest that HvVRN2 counteracts PPD-H1 to prevent flowering prior to vernalization. An allele of HvVRN1 that is expressed at high basal levels (HvVRN1-1) was associated with rapid inflorescence initiation regardless of HvVRN2 or PPD-H1 genotype. HvFT1 was expressed without vernalization in lines with the HvVRN1-1 allele and HvFT1 transcript levels were highest in lines with the active PPD-H1 allele; this correlated with rapid apex development post-inflorescence initiation. Thus, expression of HvVRN1 promotes inflorescence initiation and up-regulates HvFT1. Analysis of HvVRN1 expression in different genetic backgrounds post-vernalization showed that HvVRN2, HvFT1 and PPD-H1 are unlikely to play a role in low-temperature induction of HvVRN1. In a vernalization responsive barley, HvFT1 is not induced by low-temperatures alone, but can be induced by long days following prolonged low-temperature treatment. We conclude that low-temperature and daylength flowering-response pathways are integrated to control expression of HvFT1 in barley, and that this might occur through regulation of HvVRN2 activity.






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