An Essential Role For MicroRNA 167 Genes In Maternal Control Of Embryonic And Seed Development

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 very difficult to identify because the maternal effects need to be determined or confirmed by several genetic crosses.Here we completely deleted the four MicroRNA 167(MIR167)genes in Arabidopsis using CRISPR/Cas9 genome-editing technology.We found that plants with a deletion of MIR167A phenocopied plants overexpressing miRNA167-resistant versions of ARF6 or ARF8,two miRNA167 targets.Both the mir167a mutant and the ARF overexpression lines were defective in anther dehiscence and ovule development.Serendipitously,we found that the mir167a(?)x WT(?)crosses failed to develop normal embryos and endosperms,despite that embryos with either mir167a+/-or mirl67a-/-genotypes developed normally when mir167a+/-plants were self-pollinated,revealing a central role of MIR167A in maternal control of seed development.The mir167a mutant is a great genetic tool for studying the roles of miRNAs and auxin in maternal control.Moreover,we found that mir167a mutants flowered significantly later than wild type(WT)plants,a phenotype that was not observed in the ARF overexpression lines.We show that the reproductive defects of mir167a were suppressed by a decrease of activities of ARF6,ARF8,or both.Different from the mir167a plants,mirl67bcd mutants did not display any obvious developmental defects.However,mir167bcd can enhance the defects of mirl67a in ovule and seeds development.Our results clearly demonstrate that MIR167A is the predominant MIR167 member in regulating Arabidopsis reproduction and that MIR167A acts as a maternal gene and functions largely through ARF6 and ARF8.