The CLAVATA2 ( CLV2 ) gene regulates both meristem and organ development in Arabidopsis. We isolated the CLV2 gene and found that it encodes a receptor-like protein (RLP), with a presumed extracellular domain composed of leucine-rich repeats similar to those found in plant and animal receptors, but with a very short predicted cytoplasmic tail. RLPs lacking cytoplasmic signaling domains have not been previously shown to regulate development in plants. Our prior work has demonstrated that the CLV1 receptor-like kinase (RLK) is present as a disulfide-linked multimer in vivo. We report that CLV2 is required for the normal accumulation of CLV1 protein and its assembly into protein complexes, indicating that CLV2 may form a heterodimer with CLV1 to transduce extracellular signals. Sequence analysis suggests that the charged residue in the predicted transmembrane domain of CLV2 may be a common feature of plant RLPs and RLKs. In addition, the chromosomal region in which CLV2 is located contains an extremely high rate of polymorphism, with 50 nucleotide and 15 amino acid differences between Landsberg erecta and Columbia ecotypes within the CLV2 coding sequence. INTRODUCTIONThe shoot meristem is responsible for the formation of all above-ground organs in higher plants. This task is accomplished by balancing two processes: the maintenance of a population of undifferentiated cells at the center of the shoot meristem and the direction of progeny cells on the flanks of the meristem toward organ formation and eventual differentiation. Mutations in several genes in Arabidopsis have been shown to disrupt this balance (reviewed in Clark, 1997), including SHOOT MERISTEMLESS ( STM ), WUSCHEL ( WUS ), and the genes comprising the CLAVATA loci ( CLV1 , CLV2 , and CLV3 ) (Leyser and Furner, 1992;Barton and Poethig, 1993;Clark et al., 1993Clark et al., , 1995Laux et al., 1996;Kayes and Clark, 1998). Plants carrying mutations at the CLV loci accumulate undifferentiated cells in the shoot and flower meristems, and it has therefore been proposed that the CLV genes either inhibit the division of these cells or promote their transition toward a differentiated state (reviewed in Clark, 1997).The phenotypes of clv1 and clv3 mutants are identical, and these two genes function in the same pathway to regulate meristem development. In addition, the phenotypes of the clv1 and clv3 mutants and the gene expression patterns for CLV1 and CLV3 appear to be specific to the shoot and flower meristems (Clark et al., 1993(Clark et al., , 1995Fletcher et al., 1999). Compared with clv1 and clv3 mutants, all clv2 mutant alleles display weak phenotypes at the shoot and flower meristems (Kayes and Clark, 1998). clv2 mutations also affect the development of several organ types. These include the pedicel, which is elongated in clv2 mutants, and the anthers and valves of the flower, both of which are reduced in clv2 mutants. Genetic analysis indicates that CLV2 functions in the same pathway as CLV1 and CLV3 in the regulation of meristem development but in a separa...

Intercellular signaling plays an important role in controlling cellular behavior in apical meristems and developing organs in plants. One prominent example in Arabidopsis is the regulation of floral organ shape, ovule integument morphogenesis, the cell division plane, and root hair patterning by the leucine-rich repeat receptor-like kinase STRUBBELIG (SUB). Interestingly, kinase activity of SUB is not essential for its in vivo function, indicating that SUB may be an atypical or inactive receptor-like kinase. Since little is known about signaling by atypical receptor-like kinases, we used forward genetics to identify genes that potentially function in SUB-dependent processes and found recessive mutations in three genes that result in a sub-like phenotype. Plants with a defect in DETORQEO (DOQ), QUIRKY (QKY), and ZERZAUST (ZET) show corresponding defects in outer integument development, floral organ shape, and stem twisting. The mutants also show sub-like cellular defects in the floral meristem and in root hair patterning. Thus, SUB, DOQ, QKY, and ZET define the STRUBBELIG-LIKE MUTANT (SLM) class of genes. Molecular cloning of QKY identified a putative transmembrane protein carrying four C2 domains, suggesting that QKY may function in membrane trafficking in a Ca2+-dependent fashion. Morphological analysis of single and all pair-wise double-mutant combinations indicated that SLM genes have overlapping, but also distinct, functions in plant organogenesis. This notion was supported by a systematic comparison of whole-genome transcript profiles during floral development, which molecularly defined common and distinct sets of affected processes in slm mutants. Further analysis indicated that many SLM-responsive genes have functions in cell wall biology, hormone signaling, and various stress responses. Taken together, our data suggest that DOQ, QKY, and ZET contribute to SUB-dependent organogenesis and shed light on the mechanisms, which are dependent on signaling through the atypical receptor-like kinase SUB.

MicroRNAs (miRNAs) are released from cells in association with proteins or microvesicles. We previously reported that malignant transformation changes the assortment of released miRNAs by affecting whether a particular miRNA species is released or retained by the cell. How this selectivity occurs is unclear. Here we report that selectively exported miRNAs, whose release is increased in malignant cells, are packaged in structures that are different from those that carry neutrally released miRNAs (n-miRNAs), whose release is not affected by malignancy. By separating breast cancer cell microvesicles, we find that selectively released miRNAs associate with exosomes and nucleosomes. However, n-miRNAs of breast cancer cells associate with unconventional exosomes, which are larger than conventional exosomes and enriched in CD44, a protein relevant to breast cancer metastasis. Based on their large size, we call these vesicles L-exosomes. Contrary to the distribution of miRNAs among different microvesicles of breast cancer cells, normal cells release all measured miRNAs in a single type of vesicle. Our results suggest that malignant transformation alters the pathways through which specific miRNAs are exported from cells. These changes in the particles and their miRNA cargo could be used to detect the presence of malignant cells in the body.