Tripsacum dactyloides (Poaceae): a natural model system to study parthenogenesis

Area of Science:

• Plant reproductive biology
• Genetics and genomics
• Evolutionary biology

Background:

• Gametophytic apomixis, characterized by unreduced embryo sacs and parthenogenetic embryo development, is a mode of asexual reproduction in plants.
• Tripsacum dactyloides (Eastern gamagrass) is a close relative of maize and serves as a natural model for studying apomixis due to its similar genetic background.
• Understanding the genetic mechanisms of apomixis in Tripsacum can provide insights into reproductive strategies and potential applications in crop improvement.

Purpose of the Study:

• To investigate the mechanisms of gametophytic apomixis in Tripsacum dactyloides, focusing on parthenogenesis and pseudogamy.
• To characterize the genome size of sexual and apomictic Tripsacum dactyloides using flow cytometry.
• To establish protocols for studying gene expression in apomictic embryos and embryo sacs of Tripsacum dactyloides.

Main Methods:

• Flow cytometry was used to estimate the genome size of diploid sexual and polyploid apomictic Tripsacum dactyloides.
• The flow cytometric seed screen (FCSS) was employed to quantify the rate of apomixis in tetraploid accessions.
• A transgenic maize line with an actin::β-glucuronidase (GUS) reporter construct was used to investigate fertilization-dependent endosperm formation.

Main Results:

• The diploid genome size of T. dactyloides was found to be approximately 1.35 times larger than that of maize.
• A high rate of apomixis (92%) was observed in tetraploid T. dactyloides accessions, including twin embryos in 13% of seeds.
• Autonomous embryo development and fertilization-dependent endosperm formation were confirmed, with GUS expression detected only in the endosperm after pollination.

Conclusions:

• Tripsacum dactyloides exhibits a highly efficient apomictic pathway involving diplosporous apomeiosis, parthenogenesis, and pseudogamy.
• The established protocols for microdissection and gene expression analysis provide valuable tools for future research on apomixis.
• Comparative studies between sexual maize and apomictic/sexual Tripsacum dactyloides can elucidate the genetic basis of reproductive strategies.