The microspore-derived embryo ofBrassica napus L. as a tool for studying embryo-specific lipid biogenesis and regulation of oil quality

Brassica napus Haploid and Double Haploid Production and Its Latest Applications

Rapeseed is one of the most important oil crops in the world. Increasing demand for oil and limited agronomic capabilities of present-day rapeseed result in the need for rapid development of new, superior cultivars. Double haploid (DH) technology is a fast and convenient approach in plant breeding as well as genetic research. Brassica napus is considered a model species for DH production based on microspore embryogenesis; however, the molecular mechanisms underlying microspore reprogramming are still vague. It is known that morphological changes are accompanied by gene and protein expression patterns, alongside carbohydrate and lipid metabolism. Novel, more efficient methods for DH rapeseed production have been reported. This review covers new findings and advances in Brassica napus DH production as well as the latest reports related to agronomically important traits in molecular studies employing the double haploid rapeseed lines.

Expression of the BnmNAP subfamily of napin genes coincides with the induction of Brassica microspore embryogenesis

Brassica napus cv. Topas microspores can be diverted from pollen development toward haploid embryo formation in culture by subjecting them to a heat stress treatment. We show that this switch in developmental pathways is accompanied by the induction of high levels of napin seed storage protein gene expression. Changes in the plant growth or microspore culture conditions were not by themselves sufficient to induce napin gene expression. Specific members of the napin multigene family were cloned from a cDNA library prepared from microspores that had been induced to undergo embryogenesis. The majority of napin clones represented three members (BnmNAP2, BnmNAP3 and BnmNAP4) that, along with a previously isolated napin genomic clone (BngNAP1), constitute the highly conserved BnmNAP subfamily of napin genes. Both RNA gel blot analysis, using a subfamily-specific probe, and histochemical analysis of transgenic plants expressing a BngNAP1 promoter-beta-glucuronidase gene fusion demonstrated that the BnmNAP subfamily is expressed in embryogenic microspores as well as during subsequent stages of microsporic embryo development.

Intertribal somatic hybrids between Brassica napus and Thlaspi perfoliatum with high content of the T. perfoliatum-specific nervonic acid

Protoplast fusions were performed between hypocotyl protoplasts of Brassica napus and mesophyll protoplasts of Thlaspi perfoliatum. The two species are members of the Lepidieae and Brassiceae tribes, respectively, in the family of Brassicaceae. Seeds of T. perfoliatum are rich in the fatty acid C24∶1 (nervonic acid), an oil valuable for technical purposes. In the search for renewable oils to replace the mineral oils, plant breeders have been trying to develop oil crops with a high content of long-chain fatty acids. After fusion of B. napus protoplasts with non-irradiated as well as irradiated protoplasts of T. perfoliatum selection was carried out by flow cytometry and cell sorting. Of the shoots regenerated from different calli 27 were verified as hybrids or partial hybrids using the isoenzyme phosphoglucose isomerase (PGI) as a marker. Another 6 plants were identified as partial hybrids using a T. perfoliatum-specific repetitive DNA sequence. Slot blot experiments were performed to estimate the copy number of the repetitive DNA sequence in the parental species and in the hybrids. In T. perfoliatum there were approximately 10(5) copies per haploid genome, and the range in the hybrids was 1-37% of the value in T. perfoliatum. When the nuclear DNA content of the regenerated shoots was analysed we found partial as well as symmetric hybrids. Even though the rooting and establishment of hybrid shoots in the greenhouse were difficult, resulting in the death of many plants, 19 plants were cultured to full maturity. Seeds obtained from 15 plants were analysed to determine whether they contained nervonic acid, and 5 of the hybrids were found to contain significantly greater amounts of nervonic acid than B. napus.