MpmiR319 promotes gemma/gemma cup formation in the LiverwortMarchantia polymorpha

Abstract

AbstractEvolutionally conserved miRNA-target mRNA modules have been identified as a core set of functionally and biologically important gene regulation circuits in land plants. Whether the miR159/319 family could maintain such a common biologically fundamental function remains unknown. In this study, we applied the CRISPR-Cas9 system to knock out two MpMIR319loci,MIR319aand/orMIR319b, in the liverwortMarchantia polymorphato observe phenotypic changes during development. TheMIR319bknockout line developed fewer gemma cups, while there was a decrease in the number of gemma produced per gemma cup in theMIR319aknockout line. It was predicted that miR319 targets MpRKDand MpR2R3-MYB21mRNA and suppresses their expression. To verify this, we constructed miR319-resistant MpRKD(mMpRKD) and MpR2R3-MYB21 (mMpR2R3-MYB21) genes and introduced these genes into wild-type liverwort plants to monitor phenotypic changes. We found that mMpRKDinduced gemma/gemma cup-less liverworts but mMpR2R3-MYB21 did not. These results indicate that miR319 mainly targets and represses RKD expression rather than that of R2R3-MYB21. Additionally, negative regulation of RKD expression by miR319 controls the placement and number of gemma/gemma cups produced in thalli.