Misexpression of the Homologues of Bryophyte Gametophyte-to-Sporophyte Control Genes in Arabidopsis Results in Germline Reprogramming and Phenotypes that Mirror Apomictic Development

Abstract

Evidence from the model bryophytes Physcomitrium and Marchantia suggests that a BELL-KNOX genetic module acts as a master regulator controlling sporophyte identity. Investigating any conservation of this system in flowering plants has proved challenging, but studies of the Arabidopsis eostre mutant and naturally apomictic angiosperms point to ectopic activation of KNOX and BELL transcription factors mediating the switch from sexual to apomictic development. We show here that in Arabidopsis, ectopic expression, under a germline-specific promoter, of KNOX and BELL genes not normally expressed in the gametophytes both disrupts germ cell specification and causes defects in cell identity throughout gametophyte development - some mirroring events seen in naturally apomictic plants. A better understanding of this TALE-HD genetic module in flowering plants may thus help to unravel the molecular control of higher plant life cycles, while providing a route to engineering synthetic apomixis in crops. This study also highlights the utility of applying data from bryophytes, where the ontogeny transitions are spatio-temporally distinct, to apomixis research in angiosperms.