Vivipary as a tool to analyze late embryogenic events in maize

Abstract

In maize vivipary, the precocious germination of the seed while still attached to the ear, is the diagnostic phenotype of mutants, which are impaired in the biosynthesis or response to abscisic acid (ABA). Of the 15 genes so far described, 12 control specific steps in ABA biosynthesis, two mediate hormone response and one still has an undefined role. We have analyzed a collection of 25 independent vp isolates with the aim of determining the degree of mutational saturation that has so far been reached. Of the 25 viviparous mutants complementation tested, 22 correspond to known loci: six are allelic to vp1, another six to vp5, one to vp7, two to vp9, six to vp10 and one to w3. The remaining three represent genes not previously identified. All mutants so far tested except rea show a decrease in ABA content. As to the only two mutants (vp1 and rea) whose endogenous ABA content is not impaired, the reduction in sensitivity of the double mutant compared to the single ones suggests that the two genes control separate pathways in the ABA signal transduction. Some of the mutants in this collection have a characteristic incomplete germination that allows the embryo of the mature dry seed to resume germination. By exploiting this feature it is possible to infer, through a germination test, whether the mutant has been impaired in the acquisition of desiccation tolerance. This information provides the starting point for the dissection of the genetic basis of desiccation tolerance.

Desiccation tolerance: From genomics to the field

“…For example, in Arabidopsis, seeds of the fus3-3 mutant are desiccation sensitive whereas seeds bearing the fus3-T mutation are desiccation-tolerant but exhibit reduced seed longevity in open storage [99]. In maize, the screening of 25 vp mutant seeds impaired in the synthesis of ABA to various degrees also showed a range of desiccation sensitivities [98].…”

“…ABI3, LEC2 and FUS3 are B3 transcription factors interacting with each other to regulate many developmental processes such as accumulation of storage reserves and anthocyans, precocious germination, dormancy and desiccation tolerance (for references see [26,95,96]. The severe alleles must be rescued before the loss of water during maturation kills the seeds [97,98]. Recent studies reported on mutants that exhibit a range of desiccation sensitivities, thereby providing a valuable tool for the dissection of the genetic basis of desiccation tolerance by "omics" approaches.…”

A viviparous mutant of maize exhibiting permanent water stress symptoms

“…Of the six alleles of vp10 detected in a previous screen (Durantini et al 2008), only one (vp10-108) exhibits the green shoot tip phenotype characteristic of vp10-105 in its native background. However no efforts have been made so far to assay how the genetic background affects the expression of this trait.…”

“…The only translocation uncovering the mutant was T-B10L, thus allowing the assignment of the mutant to the long arm of chromosome 10. Its complementation test with all known vp mutants with green seedlings of Class 3 (Durantini et al 2008) indicates that it is allelic to vp10, a gene encoding CNX1, a multifunctional protein which catalyzes the last step of the MoCo biosynthesis (Porch et al 2006).…”

“…The preparation of immature embryos and seedling tissues and the determination of their physiologically active ABA were performed as described in Durantini et al (2008).…”