Grasslands account for almost one quarter of the world’s cover of vegetation. Almost three quarter of the world’s milk, beef and veal are produced from temperate grasslands. In New Zealand, ryegrass (Lolium perenne) is the main pasture constituent with more than half of the total export revenue coming from grass-related products. Much of ryegrass production and quality depends on the timing of flowering through seasonal progression. In many plants, day length is the critical environmental parameter that controls when plants begin to flower. In Arabidopsis the CONSTANS (CO) gene mediates day length response. Upstream of CO is the GIGANTEA (GI) gene which is associated with the circadian clock mechanism and is required to promote CO expression. The FT gene is the immediate downstream genetic target of CO and is a direct promoter of flowering. In this study, cDNA libraries, sequence alignment and genome walking were used to sequence and describe three putative orthologues from the ryegrass photoperiod pathway: LpGI, LpCOL1, and LpFT3. All three behaved in a true photoperiod manner characterised by cycling expression patterns under continuous light conditions and differential expression patterns in LD and SD conditions. Different photoperiods brought about differences in expression of these genes measured either by the phase shift change (LpGI and LpCOL1) or by the change of the transcript level (LpFT3). Gene expression changes over a vernalisaton time course were also analysed and results indicated that LpFT3 acts as the flowering integrator. The role of LpGI, LpCOL1, and LpFT3 as putative photoperiod genes was further confirmed by genetic mapping, which placed them on linkage groups 3, 6, and 7, respectively. The syntenic positions in rice contain major heading date quantitative trait loci. The function of LpFT3 was examined by over-expressing the gene in Arabidopsis under control of the cauliflower mosiac virus (CaMV) 35S promoter. Substantially higher expression of the endogenous Arabidopsis AtFT transcript was observed in the mutated ft-1 line overexpressing LpFT3, suggesting a positive feedback loop either directly or through upstream intermediaries. Overexpression of the LpGI and LpFT3 genes restored rapid flowering to the respective gi-3 and ft-1 Arabidopsis mutants while overexpression of LpCOL1 did not accelerate flowering either in co-2 or wild type Arabidopsis plants. However, overexpression of LpCOL1 completely restored the late flowering phenotype of the gi-3 mutant indicating the existence of another important link outside the well established hierarchy of GI-CO-FT in the photoperiod pathway. This study revealed that the ryegrass photoperiod pathway genes show high similarity to their wheat, rice and Arabidopsis counterparts. Exploring ways to modulate flowering time in ryegrass could provide major benefits to the agricultural industry by increasing forage quality, controlling seed and pollen production, and addressing potential problems linked with climate change.
| Identifer | oai:union.ndltd.org:ADTP/247333 |
| Date | January 2007 |
| Creators | Gagic, Milan, 1971- |
| Publisher | ResearchSpace@Auckland |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Items in ResearchSpace are protected by copyright, with all rights reserved, unless otherwise indicated., http://researchspace.auckland.ac.nz/docs/uoa-docs/rights.htm, Copyright: The author |
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