TESTING EFFECTIVE PLOIDY IN RNA-DIRECTED DNA-METHYLATION IN THE GENUS CAPSELLA

Abstract

In plants, hybridization is an important breeding technique; however, reproductive barriers can hinder viable hybrid seed production. Interploidy and interspecific crosses are common hybridization conflicts caused by improper endosperm development, leading to embryo arrest and seed abortion. This endosperm hybridization barrier is mediated by effective ploidy as it considers both the absolute ploidy (n) and the genomic strength, determined by the mating system. The RNA-directed DNA Methylation (RdDM) pathway plays an important role in plant reproduction and seed development. The loss of RdDM reduces interploidy seed lethality in diploid by tetraploid crosses in Arabidopsis thaliana. However, this has not been studied in Capsella interspecific crosses. To test the effective ploidy of RdDM mutants in Capsella, I performed intraspecific and interspecific crosses with Capsella grandiflora and Capsella rubella, where either one or both of the parents were RdDM mutants. I observed that loss of RdDM in C. grandiflora WT x C. rubella WT resulted in slightly increased normal seed production. However, there was no change in normal seed production when C. rubella RdDM mutant was crossed with C. grandiflora. This suggests that loss of RdDM plays a greater role in seed production in C. grandiflora than C. rubella, therefore, has a greater impact on the effective ploidy of C. grandiflora.