TRANSPARENT TESTA 2 allele confers major reduction in pennycress (Thlaspi arvense L.) seed dormancy

Efforts are underway to domesticate the winter annual oilseed cover crop, pennycress (Thlaspi arvense L.), to aid in overcoming global food security and ecosystem challenges. Several key alleles for domestication have already been introgressed; however, the weedy trait of seed dormancy remains. To make pennycress attractive for growers, any traits that could contribute to weed pressure on their fields must be removed. In this study, we have performed multi-faceted experiments to understand and dissect challenges associated with seed dormancy and germination in wild pennycress. Lines were derived by chemical mutagenesis to provide a possible genetic solution. Laboratory and field-based experiments were performed to understand the role of light, seed priming, and gibberellic acid in the wild-type pennycress. These experiments were followed by incorporation of a genotype with a mutation in the TRANSPARENT TESTA 2 gene that could potentially overcome problem of seed dormancy in wild-type pennycress. Subsequent laboratory and field-based comparison of the wild-type and tt2 mutant over three seasons suggested that the tt2 line can germinate at a faster rate than wild-type and is comparable to the germination of wild-type treated with gibberellic acid. These experiments validated the hypothesis of using transparent testa mutants to solve seed dormancy and germination challenges. Further characterization of the transparent testa mutant indicated that this genotype can be susceptible to abiotic stress conditions such as NaCl, polyethylene glycol, coarse growth medium (sand), and abscisic acid. Future work is required to understand the issues related to the abiotic stress response in these lines.