Lilliputian mutant of maize lacks cell elongation and shows defects in organization of actin cytoskeleton

The maize mutant lilliputian is characterized by miniature seedling stature, reduced cell elongation, and aberrant root anatomy. Here, we document that root cells of this mutant show several defects in the organization of actin filaments (AFs). Specifically, cells within the meristem lack dense perinuclear AF baskets and fail to redistribute AFs during mitosis. In contrast, mitotic cells of wild-type roots accumulate AFs at plasma membrane-associated domains that face the mitotic spindle poles. Both mitotic and early postmitotic mutant cells fail to assemble transverse arrays of cortical AFs, which are characteristic for wild-type root cells. In addition, early postmitotic cells show aberrant distribution of endoplasmic AF bundles that are normally organized through anchorage sites at cross-walls and nuclear surfaces. In wild-type root apices, these latter AF bundles are organized in the form of symmetrically arranged conical arrays and appear to be essential for the onset of rapid cell elongation. Exposure of wild-type and cv. Alarik maize root apices to the F-actin drugs cytochalasin D and latrunculin B mimics the phenotype of lilliputian root apices. In contrast to AFs, microtubules are more or less normally organized in root cells of lilliputian mutant. Collectively, these data suggest that the LILLIPUTIAN protein, the nature of which is still unknown, impinges on plant development via its action on the actin cytoskeleton.