Roderick Scott

Double fertilization in Arabidopsis thaliana involves a polyspermy block on the egg but not the central cell

In animal reproduction, thousands of sperm may compete to fertilize a single egg, but polyspermy blocks prevent multiple fertilization that would otherwise lead to death of the embryo. In flowering plants, successful seed development requires that only two sperm are delivered to the embryo sac, where each must fertilize a female gamete (egg or central cell) to produce the embryo and endosperm. Therefore, polyspermy must be avoided, not only to prevent abnormalities in offspring, but to ensure double fertilization. It is not understood how each sperm fertilizes only one female gamete, nor has the existence of polyspermy barriers been directly tested in vivo. Here, we sought evidence for polyspermy blocks in angiosperms using the polyspermic tetraspore (tes) mutant of Arabidopsis, which allows in-vivo challenge of egg and central cell with multiple male gametes. We show that tes mutant pollen tubes can transmit more than one sperm pair to an embryo sac, and that sperm from more than one pair can participate in fertilization. We detected endosperms but not embryos with ploidies that could only result from multiple fertilization. Our results therefore demonstrate an in-vivo polyspermy block on the egg, but not the central cell of a flowering plant.

Seed colour loci, homoeology and linkage groups of the C genome chromosomes revealed in Brassica rapa–B. oleracea monosomic alien addition lines

BACKGROUND AND AIMS Brassica rapa and B. oleracea are the progenitors of oilseed rape B. napus. The addition of each chromosome of B. oleracea to the chromosome complement of B. rapa results in a series of monosomic alien addition lines (MAALs). Analysis of MAALs determines which B. oleracea chromosomes carry genes controlling specific phenotypic traits, such as seed colour. Yellow-seeded oilseed rape is a desirable breeding goal both for food and livestock feed end-uses that relate to oil, protein and fibre contents. The aims of this study included developing a missing MAAL to complement an available series, for studies on seed colour control, chromosome homoeology and assignment of linkage groups to B. oleracea chromosomes. METHODS A new batch of B. rapa-B. oleracea aneuploids was produced to generate the missing MAAL. Seed colour and other plant morphological features relevant to differentiation of MAALs were recorded. For chromosome characterization, Snows carmine, fluorescence in situ hybridization (FISH) and genomic in situ hybridization (GISH) were used. KEY RESULTS The final MAAL was developed. Morphological traits that differentiated the MAALs comprised cotyledon number, leaf morphology, flower colour and seed colour. Seed colour was controlled by major genes on two B. oleracea chromosomes and minor genes on five other chromosomes of this species. Homoeologous pairing was largely between chromosomes with similar centromeric positions. FISH, GISH and a parallel microsatellite marker analysis defined the chromosomes in terms of their linkage groups. Conclusions A complete set of MAALs is now available for genetic, genomic, evolutionary and breeding perspectives. Defining chromosomes that carry specific genes, physical localization of DNA markers and access to established genetic linkage maps contribute to the integration of these approaches, manifested in the confirmed correspondence of linkage groups with specific chromosomes. Applications include marker-assisted selection and breeding for yellow seeds.

Assigning Brassica microsatellite markers to the nine C-genome chromosomes using Brassica rapa var. trilocularis-B. oleracea var. alboglabra monosomic alien addition lines

Brassica rapa var. trilocularis–B. oleracea var. alboglabra monosomic alien addition lines (MAALs) were used to assign simple sequence repeat (SSR) markers to the nine C-genome chromosomes. A total of 64 SSR markers specific to single C-chromosomes were identified. The number of specific markers for each chromosome varied from two (C3) to ten (C4, C7 and C9), where the designation of the chromosomes was according to Cheng et al. (Genome 38:313–319, 1995). Seventeen additional SSRs, which were duplicated on 2–5 C-chromosomes, were also identified. Using the SSR markers assigned to the previously developed eight MAALs and recently obtained aneuploid plants, a new Brassica rapa–B. oleracea var. alboglabra MAAL carrying the alien chromosome C7 was identified and developed. The application of reported genetically mapped SSR markers on the nine MAALs contributed to the determination of the correspondence between numerical C-genome cytological (Cheng et al. in Genome 38:313–319, 1995) and linkage group designations. This correspondence facilitates the integration of C-genome genetic information that has been generated based on the two designation systems and accordingly increases our knowledge about each chromosome. The present study is a significant contribution to genetic linkage analysis of SSR markers and important agronomic traits in B. oleracea and to the potential use of the MAALs in plant breeding.

Optimizing the lipid profile, to produce either a palm oil or biodiesel substitute, by manipulation of the culture conditions for Rhodotorula glutinis.

Background: Lipids are an increasingly important chemical feedstock for the manufacture of biofuels, bioplastics, care products and as a food source. Developing sustainable sources of lipids, derived from oleaginous microbes, is therefore a key scientific challenge. Methodology: Design of Experiments was used to optimize the lipid production and lipid profile. Results: Here we successfully apply Design of Experiments to optimize the lipid profile in Rhodotorula glutinis to tailor the fatty acid profile. A high culture temperature and high nitrogen ratio yielded a mainly monounsaturated oil, while low temperatures and high glucose loadings gave a more saturated profile. Conclusions: On transesterification, the oil high in monounsaturated esters yielded biodiesel with fuel properties akin to rapeseed methyl ester, whereas the oil high in saturates was found to be suitable as a substitute for palm oil.

Apomeiotic pollen mother cell development in the apomictic Boechera species

Pollen mother cell (PMC) development in the apomictic Boechera species B. holboellii, B. gunnisoniana and B. divaricarpa were investigated by various cytological methods. In prophase I, in triploid species B. holboellii and B. gunnisoniana the individual chromosomes condensed into long strands within the nucleus. Then, in metaphase I, each PMC formed a restitutional nucleus thereby bypassing the rest of the first meiotic division. This is interpreted as representing apomeiosis. Subsequently, the restitution nuclei underwent a single cytokinesis as evidenced by the production of dyads. The cells within each dyad were separated by a callose wall. Most of the PMC in B. holboellii and B. gunnisoniana produced dyads, but a small proportion generated conspicuous tetrads. In contrast, diploid apomict B. divaricarpa produced only tetrads by simultaneous cytokinesis.

Liquid transport fuels from microbial yeasts – current and future perspectives

Global transportation is one of the major contributors to GHG emissions. It is essential, therefore, that renewable, carbon neutral fuels are developed to reduce the impact of this sector on the environment. Yeasts, especially Saccharomyces cerevisiae, are key to transforming renewable bioresources to fuels that can be used with little adaption to the current transport infrastructure. Yeasts demonstrate a large diversity that produces a great metabolic plasticity; as such, yeasts are able to produce a range of fuel-like molecules including alcohols, lipids and hydrocarbons. In this article the current and potential fuels produced through fermentation, the latest advances in metabolic engineering and the production of lipids suitable for biodiesel production are all reviewed.

Elevated production of the aromatic fragrance molecule, 2-phenylethanol, using Metschnikowia pulcherrima through both de novo and ex novo conversion in batch and continuous modes

Abstract BACKGROUND 2‐phenylethanol (2PE) is a fragrance molecule predominantly used in perfumes and the food industry. It can be made from petrochemicals inexpensively, however, this is unsuitable for most food applications. Currently, the main method of production for the bio‐derived compound is to extract the trace amounts found in rose petals, which is extremely costly. Potentially fermentation could provide an inexpensive, naturally sourced, alternative. RESULTS In this investigation, 2PE was produced from the yeast Metschnikowia pulcherrima, optimised in flasks before scaling to 2 L batch and continuous operation. 2PE can be produced in high titres under de novo process conditions with up to 1500 mg L−1 achieved in a 2 L stirred bioreactor. This is the highest reported de novo titre to date, and achieved through high sugar loadings coupled with low nitrogen conditions. The process successfully ran in continuous mode also, with a concentration of 650 mg L−1 of 2PE being maintained. The 2PE production was further increased by the ex novo conversion of phenylalanine and semi‐continuous solid phase extraction from the supernatant. Under optimal conditions 14 000 mg L−1 of 2PE was produced. CONCLUSIONS The work presented here offers a novel route to naturally sourced 2PE through a scalable fermentation with a robust yeast highly suited to industrial biotechnology.