NARROW SHEATH1 functions from two meristematic foci during founder-cell recruitment in maize leaf development

The narrow sheath duplicate genes (ns1 and ns2) perform redundant functions during maize leaf development. Plants homozygous for mutations in both ns genes fail to develop wild-type leaf tissue in a lateral domain that includes the leaf margin. Previous studies indicated that the NS gene product(s) functions during recruitment of leaf founder-cells in a lateral, meristematic domain that contributes to leaf margin development. A mosaic analysis was performed in which the ns1-O mutation was exposed in hemizygous, clonal sectors in a genetic background already homozygous for ns2-O. Analyses of mutant, sectored plants demonstrate that NS1 function is required in L2-derived tissue layers for development of the narrow sheath leaf domain. NS1 function is not required for development of the central region of maize leaves. Furthermore, the presence of the non-mutant ns1 gene outside the narrow sheath domain cannot compensate for the absence of the non-mutant gene within the narrow sheath domain. NS1 acts non-cell autonomously within the narrow sheath-margin domain and directs recruitment of marginal, leaf founder cells from two discrete foci in the maize meristem. Loss of NS1 function during later stages of leaf development results in no phenotypic consequences. These data support our model for NS function during founder-cell recruitment in the maize meristem.