Genetic and Environmental Factors Contributing to Reproductive Success and Failure in Potato

The foundation of potato (Solanum tuberosum) breeding and the development of new potato varieties is the crossing of parents to produce seeds that contain new combinations of alleles that may be superior to those in either parent. In this review, we begin by highlighting a signature problem of potato breeding, the widespread lack of fertility observed in many lines. We summarize normal development of male and female reproductive structures, fertilization and embryo growth. Various manifestations of male and female sterility are then described. These include defects of meiosis and mitosis, bud abscission, competition between reproductive structures and tubers for resources, and cytoplasmic male sterility. Effects of environmental determinants, such as temperature and light intensity, on fertility are discussed. Finally, suggested best practices that promote fertility are provided as a guide for those conducting breeding and genetics work with potato.

Simultaneous TALEN-mediated knockout of chrysanthemum DMC1 genes confers male and female sterility

Genome editing has become one of the key technologies for plant breeding. However, in polyploid species such as chrysanthemum, knockout of all loci of multiple genes is needed to eliminate functional redundancies. We identified six cDNAs for the CmDMC1 genes involved in meiotic homologous recombination in chrysanthemum. Since all six cDNAs harbored a homologous core region, simultaneous knockout via TALEN-mediated genome editing should be possible. We isolated the CmDMC1 loci corresponding to the six cDNAs and constructed a TALEN-expression vector bearing a CmDMC1 target site containing the homologous core region. After transforming two chrysanthemum cultivars with the TALEN-expression vector, seven lines exhibited disruption of all six CmDMC1 loci at the target site as well as stable male and female sterility at 10–30 °C. This strategy to produce completely sterile plants could be widely applicable to prevent the risk of transgene flow from transgenic plants to their wild relatives.

Evolution of multiple postzygotic barriers between species of the Mimulus tilingii complex

ABSTRACTSpecies are often defined by their ability to interbreed (i.e., Biological Species Concept), but determining how and why reproductive isolation arises between new species can be challenging. In the Mimulus tilingii species complex, three species (M. caespitosa, M. minor, and M. tilingii) are largely allopatric and grow exclusively at high elevations (>2000m). The extent to which geographic separation has shaped patterns of divergence among the species is not well understood. In this study, we determined that the three species are morphologically and genetically distinct, yet recently diverged (<400kya). Additionally, we performed reciprocal crosses within and between the species and identified several strong postzygotic reproductive barriers, including hybrid seed inviability, F1 hybrid necrosis, and F1 hybrid male and female sterility. In this study, such postzygotic barriers are so strong that a cross between any species pair in the M. tilingii complex would cause nearly complete reproductive isolation. We consider how geographical and topographical patterns may have facilitated the evolution of several postzygotic barriers and contributed to speciation of closely related members within the M. tilingii species complex.

ZmMTOPVIB is essential for double-strand break formation and bipolar spindle assembly during maize meiosis

The programmed formation of DNA double-strand breaks (DSBs) during early meiosis is catalyzed by SPO11, a conserved ortholog to the A subunit of an archaeal topoisomerase VI (TopoVI) which functions as a hetero-tetramer comprising two A and two B subunits. An essential role of the meiotic TopoVI B subunit (TopVIB) in DSB formation has been reported in mouse, Arabidopsis and rice. Very recently, rice MTopVIB was revealed to have an unexpected role in meiotic bipolar spindle assembly, highlighting multiple functions of MTopVIB during rice meiosis. In this work, the meiotic TopVIB in maize (ZmMTOPVIB) was characterized. The ZmmtopVIB mutant plants exhibited normal vegetative growth but male and female sterility. DSB formation is abolished in mutant meiocytes. Despite normal assembly of axial elements, synapsis was severely affected and homologous pairing was disrupted in mutants. Importantly, we showed that bipolar spindle assembly was also affected in ZmmtopVIB, resulting in triad and polyad formation. Overall, our results demonstrate that ZmMTOPVIB plays critical roles in DSB formation and homologous recombination. In addition, the newly-discovered function of MTOPVIB in bipolar spindle assembly is likely conserved across different monocots.One-sentence summaryThe dual roles of MTOPVIB in regulating meiotic DSB formation and bipolar spindle assembly are evolutionarily conserved in monocot plants.

Increased Flower Longevity in Petunia with Male Sterility

Flower longevity is an important character in many ornamental crops. The processes of pollination and fertilization can cause senescence of the petals through the action of ethylene or its precursors. Preventing the production of pollen and therefore pollination could delay the senescence of petals. We tested whether male-sterility would increase flower longevity in petunia. The gene consisted of a stamen-specific promoter isolated from a Lycopersicon esculentum gene driving the expression of a barnase. Barnase is a RNase that is cytotoxic. The gene was introduced into `Lavender Storm' and `Purple Wave' petunia by Agrobacterium- mediated gene transfer. Five independent transgenic lines of both cultivars were regenerated, rooted, and grown in a greenhouse. All lines showed complete male-sterility as measured by the lack of detectable pollen. Two transgenic lines and a non-transformed control of each cultivar were propagated vegetatively and the flower longevity of each genotype was determined in a greenhouse experiment. There were two treatments: no pollination or pollination with cross-compatible pollen. All sterile genotypes that were not pollinated had increased flower longevity relative to pollinated sterile flowers or either treatment of male fertile (non-transformed) genotypes. These results indicate an application for sterility in the production of petunia flowers with increased longevity. Male and female sterility may be applicable in other ornamental crops where pollination or fertilization is a trigger to petal senescence.