An Essential Role for miRNA167 in Maternal Control of Embryonic and Seed Development

Abstract

Maternal cells play a critical role in ensuring the normal development of embryos, endosperms, and seeds. Mutations that disrupt the maternal control of embryogenesis and seed development are difficult to identify. Here, we completely deleted four <i>MICRORNA167</i> (<i>MIR167</i>) genes in Arabidopsis (<i>Arabidopsis thaliana</i>) using a clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein9 (Cas9) genome-editing technology. We found that plants with a deletion of <i>MIR167A</i> phenocopied plants overexpressing miRNA167-resistant versions of <i>Auxin Response Factor6</i> (<i>ARF6</i>) or <i>ARF8</i>, two miRNA167 targets. Both the <i>mir167a</i> mutant and the <i>ARF</i> overexpression lines were defective in anther dehiscence and ovule development. Serendipitously, we found that the <i>mir167a</i> (♀) × wild type (♂) crosses failed to produce normal embryos and endosperms, despite the findings that embryos with either <i>mir167a^+/-</i> or <i>mir167a^-/-</i> genotypes developed normally when <i>mir167a^+/-</i> plants were self-pollinated, revealing a central role of <i>MIR167A</i> in maternal control of seed development. The <i>mir167a</i> phenotype is 100% penetrant, providing a great genetic tool for studying the roles of miRNAs and auxin in maternal control. Moreover, we found that <i>mir167a</i> mutants flowered significantly later than wild-type plants, a phenotype that was not observed in the <i>ARF</i> overexpression lines. We show that the reproductive defects of <i>mir167a</i> mutants were suppressed by a decrease of activities of <i>ARF6</i>, <i>ARF8</i>, or both. Our results clearly demonstrate that <i>MIR167A</i> is the predominant <i>MIR167</i> member in regulating Arabidopsis reproduction and that <i>MIR167A</i> acts as a maternal gene that functions largely through <i>ARF6</i> and <i>ARF8</i>.