LARP6C regulates selective mRNA translation to promote pollen tube guidance in Arabidopsis thaliana.

In angiosperms, non-motile sperm cells are delivered to the ovules for fertilization via a guided growth of the pollen tube. RNA binding proteins are key regulators that control mRNA fate post-transcriptionally and thus essential for normal cell function. But very little is known on the mechanistic bases of mRNA regulations and trans-acting factors governing male-female signalling. Here we demonstrate that the evolutionarily conserved RNA binding protein LARP6C is necessary for pollen tube guidance and fertilization. larp6c loss-of-function mutants exhibit male induced fertility defects as mutant pollen tubes frequently are unable to find ovules for fertilization. In mature pollen, LARP6C localises with a pollen specific poly(A) binding protein to cytoplasmic foci likely containing mRNPs. With RNA immunoprecipitation and sequencing, we demonstrate that LARP6C is associated in vivo with mRNAs required for pollen tube guidance or polarized cell growth. We further demonstrate using in vitro and in planta transient assays that LARP6C binds 5-UTR box motifs to orchestrate the balance between translation, decay and storage of its mRNA targets. We propose a model where LARP6C maintains its mRNA target in translationally silent state likely to promote localized translation and guided pollen tube growth upon paracrine signalling.