| Summary: | <p>Abstract</p> <p>Background</p> <p>Throughout their lives plants produce new organs from groups of pluripotent cells called meristems, located at the tips of the shoot and the root. The size of the shoot meristem is tightly controlled by a feedback loop, which involves the homeodomain transcription factor WUSCHEL (WUS) and the CLAVATA (CLV) proteins. This regulatory circuit is further fine-tuned by morphogenic signals such as hormones and sugars.</p> <p>Results</p> <p>Here we show that a family of four plant-specific proteins, encoded by the <it>FANTASTIC FOUR </it>(<it>FAF</it>) genes, has the potential to regulate shoot meristem size in <it>Arabidopsis thaliana</it>. <it>FAF2 </it>and <it>FAF4 </it>are expressed in the centre of the shoot meristem, overlapping with the site of <it>WUS </it>expression. Consistent with a regulatory interaction between the <it>FAF </it>gene family and <it>WUS</it>, our experiments indicate that the FAFs can repress <it>WUS</it>, which ultimately leads to an arrest of meristem activity in <it>FAF </it>overexpressing lines. The finding that meristematic expression of <it>FAF2 </it>and <it>FAF4 </it>is under negative control by CLV3 further supports the hypothesis that the FAFs are modulators of the genetic circuit that regulates the meristem.</p> <p>Conclusion</p> <p>This study reports the initial characterization of the <it>Arabidopsis thaliana FAF </it>gene family. Our data indicate that the <it>FAF </it>genes form a plant specific gene family, the members of which have the potential to regulate the size of the shoot meristem by modulating the CLV3-WUS feedback loop.</p>
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