Functional Analysis of OsVP1 Using Rice Mutant Lines

ABA-Insensitive3/Viviparous1 (ABI3/VP1) genes encode transcription factors involved in ABA signal transduction. The objective of this research is the functional analysis of OsVP1 gene - ortholog of the maize VP1 and Arabidopsis ABI3 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 compared in the 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 seedlings 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 with no yield. 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 in seedlings of both wild type and mutant plants. Gene expression analysis was 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 at OsVP1 promoter region, which were expected because the T-DNA insertion carries several enhancers from 35S promoter of cauliflower mosaic virus. Therefore, it seems OsVP1 encodes a transcription factor which can play a role in ABA signal transduction pathway and stress induced growth arrest.