Maize ZmRPH1 Encodes a Microtubule-Associated Protein that Controls Plant and Ear Height.

Plant height is an important agronomic trait in maize since it can significantly affect planting density and lodging resistance and it is highly correlated with grain yield. Plant height of maize largely results from stem elongation driven by cell division and cell expansion within the internodes. Therefore, reduction of plant height can be achieved by appropriate control of cell elongation. The microtubule cytoskeleton plays essential roles in cellular organization, cell division and guiding plant cell polar growth, which is dependent on its organization and dynamics regulated by a suit of diverse microtubule-associated proteins (MAPs). In this study, we identified a novel MAP, Reducing Plant Height 1 (ZmRPH1), in maize. We found that ZmRPH1 bound to microtubules in vitro and in vivo and ZmRPH1 overexpression significantly led to randomly oriented cortical microtubules and considerably reduced the cell elongation in maize mesocotyl cells as well as in Arabidopsis hypocotyl cells. More importantly, we demonstrated that ZmRPH1 overexpression in maize effectively reduced plant and ear heights by repressing internode elongation, with no apparent effect on grain yield. Our work identified a valuable plant-height gene ZmRPH1 that will be useful for molecular breeding to improve plant height and lodging resistant traits in maize. This study also indicated that manipulation of cortical microtubule arrays could be a practical and efficient new strategy to optimize plant height, and will greatly benefit future maize breeding for increasing planting density.