Cloning and expression of a sorghum gene with homology to maize vp1. Its potential involvement in pre-harvest sprouting resistance

Pre-harvest sprouting (PHS) in sorghum is related to the lack of a normal d ormancy level during seed development and maturation. Based on previous evi dence that seed dormancy in maize is controlled by the vp1 gene, we used a PCR-based approach to isolate two Sorghum bicolor genomic and cDNA clones f rom two genotypes exhibiting different PHS behaviour and sensitivity to abs cisic acid (ABA). The two 699 amino acid predicted protein sequences differ in two residues at positions 341 (Gly or Cys within the repression domain) and 448 (Pro or Ser) and show over 80, 70 and 60% homology to maize, rice and oat VP1 proteins respectively. Expression analysis of the sorghum vp1 gene in the two lines shows a slight ly higher level of vp1 mRNA in the embryos susceptible to PHS than in those resistant to PHS during embryogenesis. However, timing of expression was d ifferent between these genotypes during this developmental process. Whereas for the former the main peak of expression was observed at 20 days after p ollination (DAP), the peak in the latter was found at later developmental s tages when seed maturation was almost complete. Under favourable germination conditions and in the presence of fluridone (a n inhibitor of ABA biosynthesis), sorghum vp1 mRNA showed to be consistentl y correlated with sensitivity to ABA but not with ABA content and dormancy.