ABA-Insensitive3/Viviparous1 ( ABI3/VP1 ) genes encode transcription factors are involved in ABA signal transduction. The viviparous-1 (vp1) gene in maize controls multiple developmental responses associated with the maturation phase of seed formation. Null alleles of ABI3 and VP1 result in loss of ABA sensitivity, leading to non-dormancy or vivipary in Arabidopsis and maize, respectively. In Arabidopsis plants, ABI3 is the regulator of a large number of ABA responsive genes. In abi3 mutants, seed development and germination is disturbed due to reduced sensitivity to ABA . In rice, OsVP1 is theortholog of the maize VIVIPAROUS 1 ( VP1 ) and arabidopsis ABI3 . OsVP1 gene expression is increased significantly by drought stress and abscisic acid. The objective of this research is the functional analysis of OsVP1 gene in rice through studying related mutant lines. Therefore, characteristics of the mutants (T-DNA inserted lines in the promoter or coding region of OsVP1 gene) and wild type rice plants were comparedin vegetative and reproductive stages to clarify the role of this gene. As well, the comparative analysis of the wild and mutant lines (T-DNA inserted in the promoter of OsVP1 gene) response to abscisic acid treatment and abiotic stresses were done, in addition to the expression analysis of OsVP1 gene and the candidate downstream genes in 12 day seedling using real time PCR. Mutant plants in OsVP1 coding region were pale, subtle and short compared to the wild type, in both vegetative and reproductive growth stages. No yield was achieved by the mutant plants, as the florets contained poor, crouch and colorless anthers. Second Leaf and panicle length as well as plant height of mutants in OsVP1 promoter region were less than the wild type. Panicle emergence and grain filling were also delayed compared to the wild type. Abiotic stress induced growth reduction was observed in seedlings of both wild type and mutant plants. Gene expression analysis were revealed that OsVP1 transcripts levels have been increased under drought, salinity, cold and ABA treatments compared to the control condition. Also, OsVP1 has up regulated considerably in mutant plant in OsVP1 promoter region, which were expected because the T-DNA inserion carries several enhancers from 35S promoter of cauliflower mosaic virus.
