Sugars and the SnRKI complex

Sugars are hypothesized to be involved in responses mediated by ABA in seed maturation, dormancy and germination (Rock, 2000). Rook et al. (2001) proposed that interactions between ABA and sugar-signalling pathways shift a storage mode associated with seed development to a mobilization mode associated with germination. The sucrose non-fermenting 1 (SNF1)-related protein kinase (SnRK1) com plex is hypothesized to be a mechanism in the 'cross-talk' between sugar, hormones and the environment during seed development and germination (Bradford et al., 2003). In tomato (Lycopersicon esculentum Mill.), conditions that block germination such as dormancy, ABA, far-red light and low water potential maintain expression of SNF4. It is hypothesized that SNF1 kinase is modulated by expression of SNF4 (Bradford et al., 2003). In cereals, SnRKl was expressed with AMY1 and 2 in wheat embryos during grain development from 25 days post anthesis. SnRKl was able to inhibit the AMY promoter activity (Laurie et al., 2003). It is evident that sugar signalling interacts with ABI3 (Vpl), ABI4, ABI5 and ABI1/2. For example, ABI4 and ABI5 interact genetically in controlling several aspects of seed maturation and germination, as well as sugar metabolism and sensitivity to sugar (Brocard-Gifford et al., 2003).

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