BABY BOOM regulates early embryo and endosperm development

Abstract

The BABY BOOM (BBM) AINTEGUMENTA-LIKE (AIL) AP2/ERF domain transcription factor is a major regulator of plant cell totipotency, as it induces asexual embryo formation when ectopically expressed. Surprisingly, only limited information is available on the role of <i>BBM</i> during zygotic embryogenesis. Here we reexamined <i>BBM</i> expression and function in the model plant <i>Arabidopsis thaliana</i> (<i>Arabidopsis</i>) using reporter analysis and newly developed CRISPR mutants. <i>BBM</i> was expressed in the embryo from the zygote stage and also in the maternal (nucellus) and filial (endosperm) seed tissues. Analysis of CRISPR mutant alleles for <i>BBM</i> (<i>bbm-cr</i>) and the redundantly acting <i>AIL</i> gene <i>PLETHORA2</i> (<i>PLT2</i>) (<i>plt2-cr</i>) uncovered individual roles for these genes in the timing of embryo progression. We also identified redundant roles for <i>BBM</i> and <i>PLT2</i> in endosperm proliferation and cellularization and the maintenance of zygotic embryo development. Finally, we show that ectopic <i>BBM</i> expression in the egg cell of <i>Arabidopsis</i> and the dicot crops <i>Brassica napus</i> and <i>Solanum lycopersicon</i> is sufficient to bypass the fertilization requirement for embryo development. Together these results highlight roles for <i>BBM</i> and <i>PLT2</i> in seed development and demonstrate the utility of <i>BBM</i> genes for engineering asexual embryo development in dicot species.