Overexpression of KNAT1 in lettuce shifts leaf determinate growth to a shoot-like indeterminate growth associated with an accumulation of isopentenyl-type cytokinins

Leaves are specialized organs characterized by defined developmental destin y and determinate growth. The overexpression of Knotted1-like homeobox gene s in different species has been shown to alter leaf shape and development, but a definite role for this class of genes remains to be established. Tran sgenics that overexpress Knotted1-like genes present some traits that are c haracteristic of altered cytokinin physiology. Here we show that lettuce (L actuca sativa) leaves that overexpress KNAT1, an Arabidopsis kn1-like gene, acquire characteristics of indeterminate growth typical of the shoot and t hat this cell fate change is associated with the accumulation of specific t ypes of cytokinins. The possibility that the phenotypic effects of KNAT1 ov erexpression may arise primarily from the modulation of local ratios of dif ferent cytokinins is discussed.