The filifolium1 mutation perturbs shoot architecture in Zea mays (Poaceae)

Plant architecture is elaborated through the activity of shoot apical meristems (SAMs), which produce repeating units known as phytomers, that are comprised of leaf, node, internode, and axillary bud. Insight into how SAMs function and how individual phytomer components are related to each other can been obtained through characterization of recessive mutants with perturbed shoot development. In this study, we characterized a new mutant to further understand mechanisms underlying shoot development in maize. The filifolium1-0 (ffm1-0) mutants develop narrow leaves on dwarfed shoots. Shoot growth often terminates at the seedling stage from depletion of the SAM, but if plants survive to maturity they are invariably bushy. KN1-like homeobox (KNOX) proteins are inappropriately regulated in mutant apices, adaxial identity is not specified in mutant leaves, and axillary meristems develop precociously. We propose that FFM1 acts to demarcate zones within the SAM so that appropriate fates can be conferred on cells within those zones by other factors. On the basis of the mutant phenotype, we also speculate about different relationships between phytomer components in maize and Arabidopsis.