APETALA2 regulates the stem cell niche in the Arabidopsis shoot meristem

Abstract

Postembryonic organ formation in higher plants relies on the activity of stem cell niches in shoot and root meristems where differentiation of the resident cells is repressed by signals from surrounding cells. We searched for mutations affecting stem cell maintenance and isolated the semidominant 128 mutant, which displays premature termination of the shoot meristem and differentiation of the stem cells. Allele competition experiments suggest that 128 is a dominant-negative allele of the APETALA2 (AP2) gene, which previously has been implicated in floral patterning and seed development. Expression of both WUSCHEL (WUS) and CLAVATA3 (CLV3) genes, which regulate stem cell maintenance in the wild type, were disrupted in 128 shoot apices from early stages on. Unlike in floral patterning, AP2 mRNA is active in the center of the shoot meristem and acts via a mechanism independent of AGAMOUS, which is a repressor of WUS and stem cell maintenance in the floral meristem. Genetic analysis shows that termination of the primary shoot meristem in 128 mutants requires an active CLV signaling pathway, indicating that AP2 functions in stem cell maintenance by modifying the WUS-CLV3 feedback loop. © 2005 American Society of Plant Biologists.