Development of a novel recessive genetic male sterility system for hybrid seed production in maize and other cross-pollinating crops.

We have developed a novel hybridization platform that utilizes nuclear male sterility to produce hybrids in maize and other cross-pollinating crops. A key component of this platform is a process termed Seed Production Technology (SPT). This process incorporates a transgenic SPT maintainer line capable of propagating nontransgenic nuclear male-sterile lines for use as female parents in hybrid production. The maize SPT maintainer line is a homozygous recessive male sterile transformed with a SPT construct containing (i) a complementary wild-type male fertility gene to restore fertility, (ii) an α-amylase gene to disrupt pollination and (iii) a seed colour marker gene. The sporophytic wild-type allele complements the recessive mutation, enabling the development of pollen grains, all of which carry the recessive allele but with only half carrying the SPT transgenes. Pollen grains with the SPT transgenes exhibit starch depletion resulting from expression of α-amylase and are unable to germinate. Pollen grains that do not carry the SPT transgenes are nontransgenic and are able to fertilize homozygous mutant plants, resulting in nontransgenic male-sterile progeny for use as female parents. Because transgenic SPT maintainer seeds express a red fluorescent protein, they can be detected and efficiently separated from seeds that do not contain the SPT transgenes by mechanical colour sorting. The SPT process has the potential to replace current approaches to pollen control in commercial maize hybrid seed production. It also has important applications for other cross-pollinating crops where it can unlock the potential for greater hybrid productivity through expanding the parental germplasm pool.

The transformation of anthers in the msca1 mutant of maize.

In normal anther development in maize (Zea mays L), large hypodermal cells in anther primordia undergo a series of proscribed cell divisions to form an anther containing microsporogenous cells and three distinctive anther wall layers: the tapetum, the middle layer and the endothecium. In homozygous msca1 mutants of maize, stamen primordia are initiated normally and large hypodermal cells can be detected in developing anthers. However, the normal series of cell division and differentiation events does not occur in msca1 mutant plants. Rather, structures containing parenchymal cells and ectopic, nonfunctional vascular strands are formed. The epidermal surfaces of these structures contain stomata, which are normally absent in maize anthers. Thus, all of the cell layers of the "anther" have been transformed in mutant plants. The filaments of the mutant structures are normal, and all other flower parts are normal. The msca1 mutation does not affect female fertility, but transformed "stamen" structures remain associated with mature ovules rather than aborting as in normal ear development. The msca1 mutation is distinctive in that only one part of a single (male) reproductive organ is transformed. The resulting structure has general vegetative features, but cannot be conclusively identified as a particular vegetative organ.