Single-cell transcriptome profiling of buffelgrass (Cenchrus ciliaris) eggs unveils apomictic parthenogenesis signatures

Apomixis, a type of asexual reproduction in angiosperms, results in progenies that are genetically identical to the mother plant. It is a highly desirable trait in agriculture due to its potential to preserve heterosis of F1 hybrids through subsequent generations. However, no major crops are apomictic. Deciphering mechanisms underlying apomixis becomes one of the alternatives to engineer self-reproducing capability into major crops. Parthenogenesis, a major component of apomixis, commonly described as the ability to initiate embryo formation from the egg cell without fertilization, also can be valuable in plant breeding for doubled haploid production. A deeper understanding of transcriptional differences between parthenogenetic and sexual or non-parthenogenetic eggs can assist with pathway engineering. By conducting laser capture microdissection-based RNA-seq on sexual and parthenogenetic egg cells on the day of anthesis, a de novo transcriptome for the Cenchrus ciliaris egg cells was created, transcriptional profiles that distinguish the parthenogenetic egg from its sexual counterpart were identified, and functional roles for a few transcription factors in promoting natural parthenogenesis were suggested. These transcriptome data expand upon previous gene expression studies and will be a resource for future research on the transcriptome of egg cells in parthenogenetic and sexual genotypes.

Irradiation and Heat Affect Peach Pollen Germination and Fertility

Pollen from the doubled haploid peach [Prunus persica (L.) Batsch] `Hall-D' was irradiated with 0, 290, 530, 820, 1000, 5000, or 9000 Gray (Gy) of gamma radiation, 113 μW·cm-2 of ultraviolet (UV) radiation, or exposed to 100 °C for 2 h. In vitro pollen germination percentages were recorded and pollen was used to pollinate more than 10,000 emasculated or male-sterile peach flowers. Although pollen germination in vitro was stimulated by <1000 Gy of gamma irradiation, seed set following pollination was greatly reduced in all treatments. These results suggest that low levels of irradiation are sufficient to render pollen infertile while still maintaining germination capacity. Such results may be useful for pollination-induced parthenogenetic egg division for the production of maternally derived haploids and for the production of interspecific hybrids.