The Rab Geranylgeranyl Transferase Beta Subunit Is Essential for Embryo and Seed Development in Arabidopsis thaliana

Auxin is a key regulator of plant development affecting the formation and maturation of reproductive structures. The apoplastic route of auxin transport engages influx and efflux facilitators from the PIN, AUX and ABCB families. The polar localization of these proteins and constant recycling from the plasma membrane to endosomes is dependent on Rab-mediated vesicular traffic. Rab proteins are anchored to membranes via posttranslational addition of two geranylgeranyl moieties by the Rab Geranylgeranyl Transferase enzyme (RGT), which consists of RGTA, RGTB and REP subunits. Here, we present data showing that seed development in the rgtb1 mutant, with decreased vesicular transport capacity, is disturbed. Both pre- and post-fertilization events are affected, leading to a decrease in seed yield. Pollen tube recognition at the stigma and its guidance to the micropyle is compromised and the seed coat forms incorrectly. Excess auxin in the sporophytic tissues of the ovule in the rgtb1 plants leads to an increased tendency of autonomous endosperm formation in unfertilized ovules and influences embryo development in a maternal sporophytic manner. The results show the importance of vesicular traffic for sexual reproduction in flowering plants, and highlight RGTB1 as a key component of sporophytic-filial signaling.

CMS systems in rapeseed and their use in the breeding of domestic hybrids

Development of heterotic hybrids is the most efficient approach to solve the problem of increasing the yield of rapeseed (Brassica napus L.), a leading oilseed crop. The cytoplasmic male sterility (CMS), widely used in rapeseed hybrid seed production, makes it possible to control hybridization between female and male lines. A review of publications on the nature of CMS systems in rapeseed and their utilization in breeding is presented. In rapeseed there are more than 10 known CMS systems of alloplasmic and homoplasmic origin. The male sterility character proved to be determined by chimeric mitochondrial genes, characterized by the presence of novel transcribed open reading frames (orf). Mitochondrial CMS genes associated with nap, pol, ogu and Nsa sterility types as well as nuclear Rf genes for pollen fertility restoration were identified. Molecular marker systems for identification of CMS-inducing and male fertility restoring genes were developed. The ogu, pol, MSL and inap CMS systems are commonly used for producing industrial rapeseed hybrids. The State Register of the Russian Federation for 2019 contains rapeseed hybrids of only foreign origin. Main achievements in domestic rapeseed hybrid production are highlighted. Research and breeding institutions developed new source material for rapeseed hete rotic hybrid breeding in various regions of the country. The sterility and fertility restoration sources were received from Canadian and French institutions as well as from domestic working collections. The yield structure traits did not deteriorate after transferring hybrid maternal lines to the sterile cytoplasm, while the glucosinolate content increased when pollen fertility restoring genes were transferred into paternal lines. Dihaploid (androclinium) lines and in vitro culture of unfertilized ovules were used to accelerate the breeding process. Experimental hybrids were developed using pol and ogu CMS.

Histological Study of Expression of Seedlessness in Citrus kinokuni ‘Mukaku Kishu’ and Its Progenies

The factors of seedless expression in Citrus kinokuni hort. ex Tanaka ‘Mukaku Kishu’, ‘Southern Yellow’ {‘Tanikawa Buntan’ pummelo [an uncertain hybrid with C. maxima (Burm.) Merr.] × ‘Mukaku Kishu’}, and the hybrid seedling BSY lines of ‘Southern Yellow’ × Bu1-7 pummelo [chance seedling of ‘Suisho Buntan’ pummelo (C. maxima)] were investigated histologically. ‘Mukaku Kishu’, ‘Southern Yellow’, BSY18, and BSY21 are completely seedless, whereas others are seedy. The percentage of abnormal embryo sacs and fertilization in seedless cultivars and lines showed no differences from seedy ones, indicating that the seedlessness of ‘Mukaku Kishu’ and its progenies was not involved in abnormal embryo sacs and unfertilized ovules. In seedy cultivars and lines, embryos developed to the cotyledon stage by 14 weeks after pollination. In the seedless cultivars and lines, however, embryos only developed to the early stages of zygote or embryo development. These results indicate that the seedless expression of the seedless progenies of ‘Mukaku Kishu’ coincides with ‘Mukaku Kishu’ and is caused by an arrested seed development at the early stage.

Seed parasitism redirects ovule development in Douglas fir

Many parasitic species of insects complete their entire development in seeds. They feed off storage reserves within the ovule. These reserves only normally accumulate in fertilized ovules. Consequently, female insects that oviposit their eggs directly into the plant ovule need to be able to select correctly, as unfertilized ovules of conifers normally become so-called empty seed. We provide clear evidence that in conifers, seed-parasitizing insects do not need to discriminate between fertilized and unfertilized plant ovules when ovipositing their eggs. A host-specific insect, the chalcid Megastigmus spermotrophus Wachtl (Hymenoptera: Torymidae), lays its eggs in ovules of Douglas fir ( Pseudotsuga menziesii (Mirbel) Franco) before fertilization has taken place in the plant. Oviposition not only prevents the expected degeneration and death of unfertilized ovules, but it induces energy reserve accumulation. Ovules that would otherwise develop as empty seed are redirected in their development by the insect to provide food for the developing larvae. Instead of the insect exploiting normal events during seed development, the insect manipulates seed development for its own reproductive advantage.