Plant & Animal Genomes XVII Conference

January 10-14, 2009
Town & Country Convention Center
San Diego, CA

The Apospory Program In Sorghum Accelerates Initiation Of The Sexual Processes Of Megasporogenesis And Embryo Sac Formation

John G. Carman^{1, 2} , Michelle Jamison² , Estella Elliott² , Becky Kowallis² , Tamara Naumova³

¹  Department of Plants, Soils and Climate, Utah State University, Logan, Utah 84322-4820 USA

²  Caisson Laboratories, Inc., North Logan, Utah 84341 USA

³  Nalichnaja Street 14 ap. 59, 199406 St. Petersburg, Russia

Gametophytic apomixis in plants tends to accelerate the production of the next sporophytic generation through parthenogenesis of precociously formed unreduced eggs. In a sorghum mapping population, we noticed that megasporogenesis and embryo sac (ES) formation was accelerated, relative to ovule maturity, in aposporous compared to non aposporous segregates. To determine if this is a general characteristic of apospory in sorghum, we cytologically quantified onset timing of megasporogenesis and ES formation, relative to ovule maturity, in three sets of sorghum germplasm: i) 57 accessions, included members of all five S. bicolor subspecies, ii) an F2 mapping population (300 plants), and iii) a RIL population (117 F9). Areas of meiocytes or ES, nucelli, and integuments were obtained from optical sections of cleared sagittally oriented pistils at the meiocyte stage and the 1- and early 8-nucleate ES stages. Ovule maturity was determined by measuring ovule curvature. Area and maturity measurements were taken from 15,369 correctly staged pistils. Frequency data for aposporous initials (AI) and aposporous ES (AES) per plant were obtained from a total of 80,136 correctly staged pistils. Many plants produced AI without producing AES, which caused low R² values, 0.58, 0.25 and 0.26, for the three germplasm sets, respectively, when analyzed by linear regression. In each population, plants with high AES frequencies initiated sexual megasporogenesis and ES formation at a significantly earlier ovule maturity stage than plants with low AES frequencies. These data suggest that the apospory program in sorghum assumes control of sexual processes prior to AI and AES formation.