Plant-based vaccines: unique advantages.

Numerous studies have shown that viral epitopes and subunits of bacterial toxins can be expressed and correctly processed in transgenic plants. The recombinant proteins induce immune responses and have several benefits over current vaccine technologies, including increased safety, economy, stability, versatility and efficacy. Antigens expressed in corn are particularly advantageous since the seed can be produced in vast quantities and shipped over long distances at ambient temperature, potentially allowing global vaccination. We have expressed the B-subunit of Escherichia coli heat-labile enterotoxin and the spike protein of swine transmissible gastroenteritis virus at high levels in corn, and demonstrate that these antigens delivered in the seed elicit protective immune responses.

Targeted mapping of rye chromatin in wheat by representational difference analysis.

A targeted mapping strategy using representational difference analysis (RDA) was employed to isolate new restriction fragment length polymorphism probes for the long arm of chromosome 6 in rye (6RL), which carries a gene for resistance to Hessian fly larvae. Fragments from the 6RL arm were specifically isolated using a 'Chinese Spring' (CS) wheat - rye ditelosomic addition line (CSDT6RL) as tester, and CS and (or) CS4R as the driver for the genomic subtraction. Three RDA experiments were performed using BamHI amplicons, two of which were successful in producing low-copy clones. All low-copy clones were confirmed to have originated from 6RL, indicating substantial enrichment for target sequences. Two mapping populations, both of which are derived from a cross between two similar wheat-rye translocation lines, were used to map five RDA probes as well as five wheat probes. One of the populations was prescreened for recombinants by C-banding analysis. Fifteen loci, including seven new RDA markers, were placed on a map of the distal half of 6RL. The Hessian fly resistance gene was localized by mapping and C-banding analysis to approximately the terminal 1% of the arm. The utility of RDA as a method of targeted mapping in cereals and prospects for map-based cloning of the resistance gene are discussed.

Cytologically based physical maps of the group-2 chromosomes of wheat.

We have constructed cytologically based physical maps (CBPMs), depicting the chromosomal distribution of RFLP markers, of the group-2 chromosomes of common wheat (Triticum aestivum L. em Thell). Twenty-one homozygous deletion lines for 2A, 2B, and 2D were used to allocate RFLP loci to 19 deletion-interval regions. A consensus CBPM was colinearily aligned with a consensus genetic map of group-2 chromosomes. The comparison revealed greater frequency of recombination in the distal regions. Several molecularly tagged chromosome regions were identified which may be within the resolving power of pulsed-field gel electrophoresis. The CBPMs show that the available probes completely mark the group-2 chromosomes, and landmark loci for sub-arm regions were identified for targeted-mapping.

Cytologically based physical maps of the group 3 chromosomes of wheat.

Cytologically based physical maps for the group 3 chromosomes of wheat were constructed by mapping 25 Triticum aestivum deletion lines with 29 T. tauschii and T. aestivum RFLP probes. The deletion lines divide chromosomes 3A, 3B, and 3D into 31 discrete intervals, of which 18 were tagged by marker loci. The comparison of the consensus physical map with a consensus RFLP linkage map of the group 3 chromosomes of wheat revealed a fairly even distribution of marker loci on the long arm, and higher recombination in the distal region.

Selection for increased percentage phaseolin in common bean : 1. Comparison of selection for seed protein alleles and S1 family recurrent selection.

Two selection methods were compared to determine which was more efficient for increasing percentage phaseolin in the common bean (Phaseolus vulgaris L.). A base population consisting of families segregating for six seed protein alleles (Phas (S) , Phas (C) , Phas (T) , phas (-), lec(-), and Arcl (+)), all of which have measurable effects on percentage phaseolin, was subjected to either three cycles of S1 family recurrent selection for increased percentage phaseolin (PPS), or one cycle of selection for combinations of the protein alleles (PAS) known to have positive effects on phaseolin accumulation. One cycle of PAS resulted in an increase in percentage phaseolin that was equivalent to three cycles of PPS. Selection under both methods produced increases in several correlated traits including percentage total protein, phaseolin as a percent of total protein, mg protein/seed, and mg phaseolin/seed. The amount of nonphaseolin protein per seed decreased, while seed yield was unaffected by either selection procedure. By selecting for favorable seed protein alleles identified by electrophoresis, it was possible to rapidly increase percentage phaseolin without the need for field evaluation.

Selection for increased percentage phaseolin in common bean : 2. Changes in frequency of seed protein alleles with S1 family recurrent selection.

Recurrent selection methods are designed to increase the frequency of favorable alleles within a population(s) with each cycle of selection. Yet it is likely that different methods will change allele frequencies at different rates or may act on different alleles. To investigate the ability of S1 family selection to shift the frequencies of favorable alleles within a population of Phaseolus vulgaris (L.), we examined the changes in frequencies of six alleles (Phas (S) , Phas (C) , Phas (T) , phas (-), lec (-), and Arc1 (+)) that affect the amount of phaseolin accumulated in seeds, over three cycles of selection for increased percentage phaseolin (PPS). The frequency of alleles Phas (C) and lec (-), both of which have positive effects on percentage phaseolin, increased with selection while the frequencies of phas (-) and Arc1 (+), which have strong negative effects, decreased. The frequencies of the Phas (S) and Phas (T) alleles showed no linear trends with selection, indicating that the frequency changes may be due to random drift and not to the selection procedure. The proportion of the phenotypic variation (R (2)) for percentage phaseolin that was explained by each of the alleles, and by all the alleles combined, changed with each cycle of selection. In most cases the change resulted in a decrease in the R (2) value. In this population, S1 family selection was effective at increasing the frequencies of all favorable alleles except Phas (T) , and rapidly decreased the frequencies of deleterious alleles.