RESEARCH PAPER |
Short, direct repeats (SDRs)-mediated post-transcriptional processing of a transcription factor gene OsVP1 in rice (Oryza sativa)
1Ministry of Education Key Laboratory for Bio-resource and Eco-environment, College of Life Science, Sichuan University, Chengdu 610064, China
2Ministry of Education Key Laboratory for Biodiversity Science and Ecological Engineering, Institute of Biodiversity Science, Fudan University, Shanghai 200433, China
3Institute of Crop Research, Sichuan Academy of Agricultural Sciences, Chengdu 610066, China
4State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University, Chengdu 610064, China
To whom correspondence should be addressed. E-mail: liuyongsheng1122{at}yahoo.com.cn
The various degrees of preharvest sprouting occurring in hybrid rice is a limiting factor in the propagation and production of hybrid rice seeds. The phenotype of sprouted rice is very similar to that of the maize (Zea mays) seed-specific mutation viviparous 1. VP1 has been shown to be a transcription factor essential for seed maturation and dormancy induction. In this study, numerous truncated transcripts of OsVP1 resulting from an unusual post-transcriptional processing, were detected in four rice (Oryza sativa) cultivars. The observed events took place at a region spanning exons 1 to 5, and led to a variety of deletions that resulted in the loss of functional domain and frame-shifts with premature termination by introducing a stop codon. Various proportions of the transcripts expressed in both immature and mature embryos were observed to be incorrectly processed and associated with the genetic variation of preharvest sprouting rates among various rice varieties. In sprouting-susceptible rice cultivars, G46B and HeiB, many more incorrectly processed OsVP1 transcripts were expressed in immature than in mature embryos, indicating that the unusual post-transcriptional processing of the OsVP1 gene was developmentally regulated. In addition, comprehensive sequence analyses demonstrated the presence of paired short direct repeats (SDRs) at the junctions of the unusual excision sites in exons of OsVP1 gene. Site selection for the deletion of exon materials was altered along with the genotypes and developmental stages.
Key words: Alternative splicing, Oryza sativa, preharvest sprouting, short direct repeats, vivipary 1
* These authors contributed equally to this work.
Received 2 June 2007; Revised 2 September 2007 Accepted 3 September 2007