In many cereal crops, meiotic crossovers predominantly occur toward the ends of chromosomes and 30 to 50% of genes rarely recombine. This limits the exploitation of genetic variation by plant breeding. Previous reports demonstrate that chiasma frequency can be manipulated in plants by depletion of the synaptonemal complex protein ZIPPER1 (ZYP1) but conflict as to the direction of change, with fewer chiasmata reported in Arabidopsis thaliana and more crossovers reported for rice (Oryza sativa). Here, we use RNA interference (RNAi) to reduce the amount of ZYP1 in barley (Hordeum vulgare) to only 2 to 17% of normal zygotene levels. In the ZYP1 RNAi lines, fewer than half of the chromosome pairs formed bivalents at metaphase and many univalents were observed, leading to chromosome nondisjunction and semisterility. The number of chiasmata per cell was reduced from 14 in control plants to three to four in the ZYP1-depleted lines, although the localization of residual chiasmata was not affected. DNA double-strand break formation appeared normal, but the recombination pathway was defective at later stages. A meiotic time course revealed a 12-h delay in prophase I progression to the first labeled tetrads. Barley ZYP1 appears to function similarly to ZIP1/ZYP1 in yeast and Arabidopsis, with an opposite effect on crossover number to ZEP1 in rice, another member of the Poaceae.

Blackcurrant (Ribes nigrum L.) is a widely grown commercial crop valued for its high vitamin C (l-ascorbic acid, AsA) content. In the present study, a systematic analysis of the mechanism of fruit AsA accumulation was undertaken. AsA accumulation occurred during fruit expansion and was associated with high in situ biosynthetic capacity via the l-galactose pathway and low rates of turnover. Cessation of AsA accumulation was associated with reduced biosynthesis and increased turnover. Translocation of AsA from photosynthetic or vegetative tissues contributed little to fruit AsA accumulation. Manipulation of substrate availability by defoliation had no effect on fruit AsA concentration but significantly reduced fruit yields. Supply of the AsA precursor l-galactono-1,4-lactone to intact, attached fruit transiently increased fruit AsA concentration which rapidly returned to control levels after removal of the compound. These data suggest strong developmental, metabolic and genetic control of AsA accumulation in blackcurrant fruit and indicate the potential for breeding high AsA cultivars.

Despite conservation of the process of meiosis, recombination landscapes vary between species, with large genome grasses such as barley ( Hordeum vulgare L.) exhibiting a pattern of recombination that is very heavily skewed to the ends of chromosomes. We have been using a collection of semi-sterile desynaptic meiotic mutant lines to help elucidate how recombination is controlled in barley and the role of the corresponding wild-type (WT) meiotic genes within this process. Here we applied a combination of genetic segregation analysis, cytogenetics, and immunocytology to genetically map and characterize the meiotic mutant desynaptic5 ( des5 ). We identified an exonic insertion in the positional candidate ortholog of Disrupted Meiotic cDNA 1 ( HvDMC1 ) on chromosome 5H of des5 . des5 exhibits a severe meiotic phenotype with disturbed synapsis, reduced crossovers, and chromosome mis-segregation. The meiotic phenotype and reduced fertility of des5 is similarly observed in Hvdmc1 RNAi transgenic plants and HvDMC1 p:GusPlus reporter lines show DMC1 expression specifically in the developing inflorescence. The des5 mutation maintains the reading frame of the gene and exhibits semi-dominance with respect to recombination in the heterozygote indicating the value of non-knockout mutations for dissection of the control of recombination in the early stages of meiosis.