Submitted to: Development
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/25/2004
Publication Date: 2/1/2005
Citation: Carles, C.C., Choffnes-Inada, D., Reville, K., Lertpiriyapong, K., Fletcher, J.C. 2005. ULTRAPETALA1 encodes a SAND domain putative transcriptional regulator that controls shoot and floral meristem activity in Arabidopsis. Development, 132:897-911. Interpretive Summary: This article reports the cloning, expression pattern and function of the Arabidopsis ULTRAPETALA1 (ULT1) gene in regulating shoot and flower development. The ULT1 gene has previously been shown to limit the number of stem cells that are produced by Arabidopsis shoot and floral meristems. We cloned the ULT1 gene and found that it is a member of a small gene family in plants that have the characteristics of transcriptional gene regulators. We find that ULT1 and its sister gene ULT2 are expressed throughout developing embryos, but become restricted to shoot and floral meristem cells. In developing flowers, ULT1 and ULT2 are found in the male and female reproductive organs, and in ovules. ULT1 is also expressed in vegetative meristems, and ULT2 in root meristems. Our results demonstrate that ULT1 and ULT2 have overlapping expression patterns and functions during plant development, and may regulate a number of common target genes.
Technical Abstract: The higher-plant shoot apical meristem is a dynamic structure continuously producing cells that become incorporated into new leaves, stems and flowers. The maintenance of a constant flow of cells through the meristem depends on coordination of two antagonistic processes, self-renewal of the stem cell population and initiation of the lateral organs. This coordination is stringently controlled by gene networks that contain both positive and negative components. We have previously defined the ULTRAPETALA1 (ULT1) gene as a key negative regulator of cell accumulation in Arabidopsis shoot and floral meristems, because mutations in ULT1 cause the enlargement of inflorescence and floral meristems, the production of supernumerary flowers and floral organs, and a delay in floral meristem termination. Here we show that ULT1 negatively regulates the size of the WUSCHEL (WUS)-expressing organizing center in inflorescence meristems. We have cloned the ULT1 gene and find that it encodes a small protein containing a B-box-like motif and a SAND domain, a DNA binding motif previously reported only in animal transcription factors. ULT1 and its Arabidopsis paralogue ULT2 define a novel small gene family in plants. ULT1 and ULT2 are expressed coordinately in embryonic shoot apical meristems, in inflorescence and floral meristems, and in developing stamens, carpels and ovules. Additionally, ULT1 is expressed in vegetative meristem and leaf primordia. ULT2 protein can compensate for mutant ULT1 protein when overexpressed in an ult1 background, indicating that the two genes may regulate a common set of targets during plant development. The most severe ult1 allele, ult1-1, acts in a semi-dominant fashion, and the mutant protein may interfere with the function of both ULT1 and ULT2.