Ovule development and apospory in Sorghum bicolor: Identification of molecular mechanisms controlling female gamete formation

Apomixis, or asexual reproduction through seeds, is common in nature but not in agricultural crops, and the genetic control of its onset has not been characterized. An understanding of these molecular mechanisms would greatly improve agriculture by locking in advantageous traits such as hybrid vigor, or those introduced through genetic modifications. While Sorghum bicolor does not reproduce apomictically, genotypes are available that do show apospory, an element of apomixis, in a certain percentage of their ovules. Gene expression microarray studies were done to better understand the molecular mechanisms controlling ovule development and apospory in S. bicolor, a model plant for the study of apospory. Many genes were identified that were differentially regulated during all phases of ovule development and between partially aposporic and completely sexual S. bicolor. Notable findings include: dhurrin synthesis genes were modulated during normal ovule development; chromosome pairing genes were up-regulated in developing aposporic ovules; and chromosome modifying and synthesis genes were down-regulated in aposporic ovules. Further characterization of these genes was attempted using barley stripe mosaic virus as a virus-induced gene silencing vector, however these efforts were unsuccessful. While the exact mechanisms controlling aposporic development in S. bicolor have not yet been identified, this research has provided a list of candidate apospory-causing genes that can be investigated further.