ZmHO-1, a maize haem oxygenase-1 gene, plays a role in determining lateral root development.

Previous results revealed that haem oxygenase-1 (HO-1)/carbon monoxide (CO) system is involved in auxin-induced adventitious root formation. In this report, a cDNA for the gene ZmHO-1, encoding an HO-1 protein, was cloned from Zea mays seedlings. ZmHO-1 has a conserved HO signature sequence and shares highest homology with rice SE5 (OsHO-1) protein. We further discovered that N-1-naphthylacetic acid (NAA), haemin, and CO aqueous solution, led to the induction of ZmHO-1 expression as well as the thereafter promotion of lateral root development. These effects were specific for ZmHO-1 since the potent HO-1 inhibitor zinc protoporphyrin IX (ZnPPIX) differentially blocked the above actions. The addition of haemin and CO were able to reverse the auxin depletion-triggered inhibition of lateral root formation as well as the decreased ZmHO-1 transcripts. Molecular evidence showed that the haemin- or CO-mediated the modulation of target genes responsible for lateral root formation, including ZmCDK and ZmCKI2, could be blocked by ZnPPIX. Overexpression of ZmHO-1 in transgenic Arabidopsis plants resulted in promotion of lateral root development as well as the modulation of cell cycle regulatory gene expressions. Overall, our results suggested that a maize HO-1 gene is required for the lateral root formation.