The three-domain model

Blade outgrowth and region-specific cell differentiation are crucial events during the early development of plant leaves, and the progression of both of these events requires a normal adaxial-abaxial pattern. In a recent study, we had demonstrated that two WUSCHEL-RELATED HOMEOBOX (WOX) family genes, i.e., PRESSED FLOWER (PRS) and WOX1, act redundantly in blade outgrowth and adaxial-abaxial patterning. During leaf development, the two genes are expressed in the domain between the adaxial and abaxial domains, designated "the middle domain." Together with additional data, we recently proposed "the three-domain model" in which the middle domain is distinct from the adaxial and abaxial domains and plays a key role in blade outgrowth and the pattern formation of the three domains through the function of two WOX genes. In this report, we provide three additional results that reinforce our model: (1) an expanded pattern of abaxial-specific MIR165A expression in prs wox1, (2) a genetic interaction between the two WOX genes and adaxial-specific REVOLUTA gene in adaxial-abaxial patterning and (3) an altered expression pattern of the middle domain-specific marker, consistent with disruption of the adaxial-abaxial pattern.