The shady side of leaf development: the role of the REVOLUTA/KANADI1 module in leaf patterning and auxin-mediated growth promotion

- HD-ZIPIIIs and KANs are pivotal in leaf ad-/abaxial patterning and shade growth.
- REV and KAN1 act antagonistically on common target genes and genetic pathways.
- HD-ZIPIIs (REV/KAN1 targets) control shade avoidance and leaf patterning.
- Auxin plays a core role in shade-induced growth and leaf development.

Leaves are present in all land plants and are specialized organs for light harvesting. They arise at the flanks of the shoot apical meristem (SAM), and develop into lamina structures that exhibit adaxial/abaxial (upper/lower side of the leaf) polarity. At the molecular level, an intricate regulatory network determines ad-/abaxial polarity in Arabidopsis thaliana leaves, where the Class III Homeodomain Leucine Zipper (HD-ZIPIII) and KANADI (KAN) proteins are key mediators. The HD-ZIPIII REVOLUTA (REV) is expressed in the adaxial domain of lateral organs, whereas KAN1 is involved in abaxial differentiation. The REV/KAN1 module directly and antagonistically regulates the expression of several genes involved in shade-induced growth and auxin biosynthetic enzymes.