Bioenergetic Activity is Correlated with Apomeiosis in Sorghum Ovules

Apomixis in angiosperms terminates sexual reproduction and produces a clonal egg (apomeiosis), which undergoes parthenogenesis, and an embryo sac, which produces endosperm with or without fertilization. Progeny of apomictic plants are maternal, a property viewed by seed producers as a potential tool for producing hybrid seed. Apomixis does not occur in major crops, but sexual termination and apomeiosis (aposporous embryo sac formation) do occur in certain sorghum lines at low frequencies. We identified in sorghum differentially expressed genes (DEG) and significant gene ontology (GO) categories that differentiated ovules of an aposporous (13.6 %) F2 sib from those of a sexual F2 sib at the megasporocyte to early embryo sac formation stages. GO terms indicated that ovules of the aposporous sib experienced elevated glucose levels. These induced ethylene and glucose signaling cascades that appeared to activate the growth modulator TORC1 by silencing the energy sensor SnRK1 and by producing reactive oxygen species scavengers that silenced the stress sensor SnRK2. Saturated loop design: two sibs from an F2 population, 151 and 264, with 13.6 and 0.0 % aposporous embryo sac formation, respectively (BMC Plant Biol 11, 9. doi: 10.1186/1471-2229-11-9) were selected for gene expression profiling of ovule tissues. Twenty tiller-propagated clones of each were grown. Three germline stages were chosen for profiling: early MMC, early meiocyte, and mid ES stages. Ovules were excised from pistils, and 30 samples (90-150 ovules each), five for each sib by stage combination, were collected for a total of 601, 699 and 499 ovules and 508, 604 and 499 ovules for the MMC, meiocyte and early ES stages of sexual sib 264 and aposporous sib 151, respectively. A saturated loop design was used to distribute the 30 sib/stage/replication samples (2:3:5) evenly among the 15 arrays. both channels of the array were used for data collection.