The maize CRINKLY4 receptor kinase controls a cell-autonomous differentiation response

The maize (Zea mays) CRINKLY4 (cr4) gene encodes a receptor-like kinase that controls a variety of cell differentiation responses, particularly in the leaf epidermis and in the aleurone of the endosperm. In situ hybridization indicated that the cr4 transcript is present throughout the shoot apical meristem and young leaf primordia. A genetic mosaic analysis was conducted to test whether CR4 signal transduction directly regulated the cellular processes associated with differentiation or whether differentiation was controlled through the production of a secondary signal. Genetic mosaics were created using gamma-rays to induce chromosome breakage in a cr4/Cr4+ heterozygote. The mutant cr4 allele was marked with the albino mutation, Oy-700. Breakage and loss of the chromosome arm carrying the wild-type alleles created a sector of albino, cr4 mutant tissue in an otherwise normal leaf. Analysis of such sectors indicated that cr4 functions cell autonomously to regulate cell morphogenesis, implying that CR4 signal transduction regulates cell differentiation through strictly intracellular functions and not the production of secondary intercellular signals. However, several sectors altered cell patterning in wild-type tissue adjacent to the sectors, suggesting that cr4 mutant cells are defective in the production of other lateral signals.