Submitted to: Development
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/13/2005
Publication Date: 7/20/2005
Citation: Williams, L., Grigg, S.P., Xie, M., Christensen, S., Fletcher, J.C. 2005. Regulation of Arabidopsis shoot apical meristem and lateral organ formation by microRNA miR166g and its AtHD-ZIP target genes. Development. 132:3657-3668. Interpretive Summary: Small regulatory RNAs called microRNAs have recently been discovered to be critical for the proper development of both animals and plants. Our work has shown that a microRNA named miR166g is necessary for correct shoot development in the model plant Arabidopsis thaliana. We analyzed plants that make an excess of miR166g and found that they had greatly altered architecture, including massively enlarged and split shoots, narrow leaves and reduced female reproductive structures. We showed that excess miR166g affected the activity of a genetic regulatory hierarchy that controls the accumulation of stem cells in the Arabidopsis shoot tip. Our work is the first demonstration of a key role for small regulatory RNAs in plant stem cell maintenance.
Technical Abstract: Plant development is characterized by precise control of gene regulation, leading to the correct spatial and temporal tissue patterning. We have characterized the Arabidopsis jabba-1D (jba-1D) mutant, which displays multiple enlarged shoot meristems, radialized leaves, reduced gynoecia and vascular defects. The jba-1D meristem phenotypes require WUSCHEL (WUS) activity, and correlate with a dramatic increase in WUS expression levels. We demonstrate that the jba-1D phenotypes are caused by over-expression of miR166g, and require the activity of the RNase III helicase DCL1. miR166g over-expression in jba-1D plants affects the transcripts of several class III homeodomain-leucine zipper (AtHD-ZIP) family target genes. The expression of PHABULOSA (PHB), PHAVOLUTA (PHV) and CORONA (CNA) is significantly reduced in a jba-1D background, while REVOLUTA (REV) expression is elevated and ATHB8 is unchanged. In addition, we show that miR166 has a dynamic expression pattern in wild-type and jba-1D embryos. Our analysis demonstrates an indirect role for miRNAs in controlling meristem formation via regulation of WUS expression, and reveals complex regulation of the class III AtHD-ZIP gene family.