Structural and functional properties of Viviparous1 genes in dormant wheat

Abstract

Viviparous 1 (Vp1) of maize is known to encode a transcription factor VP1 that controls seed germination. Hexaploid wheat possesses three Vp1 homoeologues (TaVp1): TaVp-A1, . In this study, we attempted to characterize the molecular properties of TaVp1 in a highly dormant wheat cultivar, Minamino-komugi (Minamino). The seeds of Minamino showed much higher sensitivity to the inhibitory effect of ABA on germination than those of non-dormant cultivars, Sanin-1 and Tozan-18. The sequence analyses of cDNAs also revealed that some of TaVp-A1 transcripts and TaVp-D1 transcripts were spliced incorrectly, presumably resulting in production of truncated or deleted proteins. Most TaVp-B1 transcripts were spliced correctly, but some had an additional 3-bp (AAG) insertion in the B3 domain, which may not affect their function. RT-PCR analyses showed that TaVp1 was highly expressed in Minamino embryos in maturing seeds but much less in roots and leaves of seedlings. The level of TaVp1 mRNA was high when the embryos were treated with ABA but markedly decreased in water-imbibed mature embryos whose dormancy had been broken. Expression analyses of the individual homoeologues showed that the level of TaVp-A1 transcripts was highest in embryos of DAP 20 but much lower in the matured embryos. TaVp-B1 was highly expressed in developing and maturing seed embryos, while TaVp-D1 mRNA existed at lower levels in developing embryos but increased as the seeds were matured. These results suggest that the majority of TaVp1, especially TaVp-B1, are properly spliced and may function as a transcription factor playing an important role on dormancy in Minamino. By employing an efficient transient expression system using diploid wheat seeds, we confirmed the dual function of TaVP-B1: the activation of Em expression and the repression of α-amylase expression.

Expression of the aldehyde oxidase 3, ent-copalyl diphosphate synthase, and VIVIPAROUS 1 genes in wheat cultivars differing in their susceptibility to pre-harvest sprouting

“…For both cultivars, in non-sprouting grains we found a higher expression level of the VP1 gene in comparison to sprouting grain but only in Piko this difference was significant. A similar correlation was found by Utsugi et al (2008) for isolated wheat embryos of dormant and dormancy-broken grains. In our research, the VP1 transcript was more abundant in non-sprouting grains of Piko (PHS-susceptible) than in non-sprouting grains of Sława (PHS-tolerant).…”

“…Several studies described the correlation between susceptibility to PHS and response of wheat grains to ABA treatment. Cultivars that are resistant / tolerant to PHS are more sensitive to ABA than susceptible cultivars (Walker-Simmons, 1987;Corbineau et al, 2000;Utsugi et al, 2008). In our studies, the grains tested after a 5-week storage showed weaker dormancy when compared to grains examined directly after harvest (45 DAP).…”

“…The expression of this gene may occur already during early stages of grain development. In wheat, the highest expression level of the VP1 gene is observed at about 50 DAP, later on -in the ripening stage (60 DAP)-it drops down (Utsugi et al, 2008). However, Wilson et al (2005) found that the expression of the VP1 gene peaked about 21 DAP, and at further stages, until 40 DAP, decreased.…”

Haplotype analysis of Viviparous-1 gene in CIMMYT elite bread wheat germplasm

“…PHS resistance has been shown to be associated not with higher ABA levels in dry seeds, but with higher ABA sensitivity during embryo maturation and during seed germination in some cultivars (Walker-Simmons 1987;Morris et al 1989). Wheat varieties showing higher seed dormancy are much more sensitive to the germination inhibitory action of exogenously applied ABA than non-dormant varieties (Walker-Simmons 1987; Morris et al 1989;Corbineau et al 2000;Utsugi et al 2008). The seeds of one Japanese wheat cultivar Minamino showed much higher sensitivity to the inhibitory effect of ABA on germination than those of nondormant cultivars, Sanin-1 and Tozan-18, and the expression of Vp-1 gene played an important role in controlling dormancy in Minamino (Utsugi et al 2008).…”

“…Wheat varieties showing higher seed dormancy are much more sensitive to the germination inhibitory action of exogenously applied ABA than non-dormant varieties (Walker-Simmons 1987; Morris et al 1989;Corbineau et al 2000;Utsugi et al 2008). The seeds of one Japanese wheat cultivar Minamino showed much higher sensitivity to the inhibitory effect of ABA on germination than those of nondormant cultivars, Sanin-1 and Tozan-18, and the expression of Vp-1 gene played an important role in controlling dormancy in Minamino (Utsugi et al 2008). In this study, we determined the GI and ABA sensitivity of eight accessions, each representing one Vp-1A haplotype.…”