The mRNA decapping machinery targetsLBD3/ASL9to mediate apical hook and lateral root development inArabidopsis

Multicellular organisms perceive and transduce multiple cues to optimize development. Key transcription factors drive developmental changes, but RNA processing also contributes to tissue development. Here, we report that multiple decapping deficient mutants share developmental defects in apical hook, primary and lateral root growth. More specifically,LATERAL ORGAN BOUNDARIES DOMAIN 3(LBD3)/ASYMMETRIC LEAVES 2-LIKE 9(ASL9) transcripts accumulate in decapping deficient plants and can be found in complexes with decapping components. Accumulation ofASL9inhibits apical hook, primary root growth and lateral root formation. Interestingly, exogenous auxin application restores lateral roots formation in bothASL9over-expressors and mRNA decay-deficient mutants. Likewise, mutations in the cytokinin transcription factors type-B ARABIDOPSIS RESPONSE REGULATORS (B-ARRs)ARR10andARR12restore the developmental defects caused by over-accumulation of cappedASL9transcript uponASL9overexpression. Most importantly, loss-of-function ofasl9partially restores apical hook and lateral root formation in decapping deficient mutants. Thus, the mRNA decay machinery directly targetsASL9transcripts for decay, possibly to interfere with cytokinin/auxin responses, during development.