Apomixis, asexual seed formation in flowering plants, produces progeny identical to the female genotype through the avoidance of meiosis and fertilization. This trait could be used as an advanced breeding tool and the ability to manipulate apomixis will have potential agronomic benefit. So far, there is no major crop that is apomictic. Therefore, discovery of the genetic mechanisms underlying apomixis would be a big step towards the long-term goal of introducing apomixis into important crops. We are working on a type of gametophytic apomixis, apospory, in Pennisetum, a member of Poaceae family. In apospory, one or more unreduced embryo sacs develop from the nucellar cells in the ovule.
This project was designed to identify expressed cDNA sequences involved in the initiation of aposporous embryo sac development in P. squamulatum. Comparative analysis of transcriptomes from microdissected nucellar tissue in P. squamulatum (PS26) and an apomictic backcross line (BC8) at early developmental stages, the point at which aposporous initials are being formed was conducted.
P. squamulatum is an apomictic species related to pearl millet (P. glaucum). An apospory-specific genomic region (ASGR) in P. squamulatum has been identified. Apomictic BC8 is a backcross line between pearl millet and PS26 with pearl millet as the recurrent parent. The ASGR-carrier chromosome is the only chromosome distinction between BC8 and pearl millet. Previous research in our lab has shown that the presence of the ASGR-carrier chromosome alone was sufficient to transfer apospory from PS26 to sexual pearl millet. Since both PS26 and BC8are aposporous and have the ASGR-carrier chromosome, it is assumed that the gene(s) controlling the initiation of apospory will have the same expression pattern at the similar developmental stage in both genotypes.
Transcript data was generated by 454-sequencing and a comparison of the two genotypes was conducted to identify expressed genes mapping to the ASGR-carrier chromosome (Zeng et al. 2011).
This work was supported by National Science Foundation award 0115911.