Transcripts of Vp - 1 homeologues are misspliced in modern wheat and ancestral species

Abstract

The maize (Zea mays) Viviparous 1 (Vp1) transcription factor has been shown previously to be a major regulator of seed development, simultaneously activating embryo maturation and repressing germination. Hexaploid bread wheat (Triticum aestivum) caryopses are characterized by relatively weak embryo dormancy and are susceptible to preharvest sprouting (PHS), a phenomenon that is phenotypically similar to the maize vp1 mutation. Analysis of Vp-1 transcript structure in wheat embryos during grain development showed that each homeologue produces cytoplasmic mRNAs of different sizes. The majority of transcripts are spliced incorrectly, contain insertions of intron sequences or deletions of coding region, and do not have the capacity to encode full-length proteins. Several VP-1-related lower molecular weight protein species were present in wheat embryo nuclei. Embryos of a closely related tetraploid species (Triticum turgidum) and ancestral diploids also contained misspliced Vp-1 transcripts that were structurally similar or identical to those found in modern hexaploid wheat, which suggests that compromised structure and expression of Vp-1 transcripts in modern wheat are inherited from ancestral species. Developing embryos from transgenic wheat grains expressing the Avena fatua Vp1 gene showed enhanced responsiveness to applied abscisic acid compared with the control. In addition, ripening ears of transgenic plants were less susceptible to PHS. Our results suggest that missplicing of wheat Vp-1 genes contributes to susceptibility to PHS in modern hexaploid wheat varieties and identifies a possible route to increase resistance to this environmentally triggered disorder.T he Viviparous1 (Vp1) gene is a major regulator of late embryo development in maize. Inactivation of this locus leads to disruption of embryo maturation, resulting in the promotion of germination of embryos while still attached to the cob (vivipary). The phenotypes of vp1 mutants show that this locus performs two distinct functions: to promote embryo maturation and embryo dormancy and simultaneously to repress germination (1, 2). Specific genes and enzyme activities have been identified that are activated or repressed by Vp1 in vivo. Expression of several enzymes (3) and maturation-related genes (4) is reduced in the mutants including those encoding seed-storage proteins and diverse LEA (late embryogenesis-abundant) proteins (1). On the other hand, ␣-amylase activity increases in the same mutants during aleurone maturation (3). These observations indicate a bifunctional role for Vp1 in regulating the balance between the activation of embryo-maturation genes and the repression of germinative hydrolases during kernel development and maturation.Orthologues of Vp1 have been cloned from rice [Osvp1 (4)], wild oat [AfVp1 (5)], and several dicotyledonous species such as Arabidopsis [ABI3 (6)] and poplar [PtABI3 (7)]. Vp1 homeologues have been mapped in wheat to the long arms of the group 3 chromosomes at a location conserved relative to Vp1 in maize and Osvp1 ...

Alternative Splicing at the Intersection of Biological Timing, Development, and Stress Responses

“…Hexaploid wheat (Triticum aestivum) varieties show weak embryo dormancy and are susceptible to preharvest sprouting, similar to maize vp1 mutants. This has been attributed to missplicing of Vp-1 homoeologs (McKibbin et al, 2002).…”

Cloning and Characterization of a Critical Regulator for Preharvest Sprouting in Wheat

“…The difference in germination temperatures between the two studies may also contribute to difference in the gene regulation. Mis-splicing in Vp1 transcripts in wheat has been shown to cause reduction in Vp1 protein activity, thus compromising the gene function (McKibbin et al 2002). The mis-splicing at position +646 of TaPHS1 together with the mutation at +666 that forms a premature stop codon results in a nonfunctional transcript, which leads to a change from a PHS-resistant genotype to a susceptible genotype.…”

Expression of the aldehyde oxidase 3, ent-copalyl diphosphate synthase, and VIVIPAROUS 1 genes in wheat cultivars differing in their susceptibility to pre-harvest sprouting

“…In the present studies, the gene encoding the VP1 transcription factor was also analyzed. The results of many reported experiments showed that in wheat cultivars which are resistant / tolerant to PHS, the level of VP1 mRNA was higher than in susceptible cultivars (Nakamura & Toyama, 2001;McKibbin et al, 2002;Rikiishi & Maekawa, 2010;De Laethauwer et al, 2012). In turn, in sorghum, the expression level of the VP1 gene in the embryos of PHS-susceptible genotypes was higher than for PHS-resistant genotypes (Carrari et al, 2001).…”

“…The VP1 gene may also be important for dormancy maintenance in wheat; in dormant cultivars, the expression of VP1 is much stronger than in non-dormant ones (Nakamura & Toyama, 2001). In turn, McKibbin et al (2002) and Wilkinson et al (2005) reported that most of the VP1 transcripts were incorrectly spliced and consequently they did not encode the full-length protein. These alternatively spliced transcripts of the VP1 gene were identified in PHS-sensitive genotypes of wheat.…”