Submitted to: Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/2004
Publication Date: 8/1/2004
Citation: Carles, C.C., Lertpiriyapong, K., Reville, K., Fletcher, J.C. 2004. The ULTRAPETALA gene functions early in Arabidopsis development to restrict shoot apical meristem activity and acts through WUSCHEL to regulate floral meristem determinacy. Genetics, 167:1893-1903. Interpretive Summary: This article reports an advance in our understanding of how the Arabidopsis ULTRAPETALA (ULT) gene product controls plant growth. Based on its mutant phenotypes, ULT has been shown to limit the number of stem cells that are produced by Arabidopsis shoot and floral meristems. We performed a genetic analysis of the interactions between ULT mutants and two previously-characterized mutants that reduce the activity of shoot and floral meristems, by generating double mutants and analyzing their phenotypes. Our results demonstrate that the ULT gene functions throughout Arabidopsis development, and that its presence is necessary for the normal timing of gene activity during flower formation.
Technical Abstract: Shoot and floral meristem activity in higher plants is controlled by complex signaling networks consisting of positive and negative regulators. The Arabidopsis ULTRAPETALA1 (ULT1) gene has been shown to act as a negative regulator of meristem cell accumulation in inflorescence and floral meristems, as loss-of-function ult1 mutations cause inflorescence meristem enlargement, the production of extra flowers and floral organs, and a decrease in floral meristem determinacy. To investigate whether ULT1 functions in known meristem regulatory pathways, we generated double mutants between ult1 alleles and null alleles of the meristem-promoting genes SHOOTMERISTEMLESS (STM) and WUSCHEL (WUS). We found that, although the ult1 alleles have no detectable embryonic or vegetative phenotypes, ult1 mutations restored extensive organ-forming capability to stm null mutants after germination and increased leaf and floral organ production in stm partial loss-of-function mutants. Mutations in ULT1 also partially suppressed the wus shoot and floral meristem phenotypes. However, wus was epistatic to ult1 in the center of the flower, and WUS transcriptional repression was delayed in ult1 floral meristems. Our results show that during the majority of the Arabidopsis life cycle ULT1 acts oppositely to STM and WUS in maintaining meristem activity, and functions in a separate genetic pathway. However, ULT1 negatively regulates WUS to establish floral meristem determinacy, acting through the WUS-AG temporal feedback loop.