Intercellular signaling processes in plants depend on two basic types of mechanisms: a combination of small ligands, capable of moving through the cell wall, and their receptors and intercellular movement of molecules passing through plasmodesmata. Cell surface receptor-like kinases naturally belong to the former class and are involved in many short-range intercellular signaling processes. The Arabidopsis genome encodes more than 600 RLK genes. This large number may relate to the salient role RLKs play in plant immunity. Several RLKs are known to be important for the Temozolomide control of organ size and shape. Well-characterized examples include the brassinosteroid hormone receptor BRASSINOSTEROID INSENSITIVE 1, the organ shape regulator ERECTA, the stem cell regulator CLAVATA1, and ARABIDOPSIS CRINKLY 4 which is involved in epidermal differentiation. ACR4 is the Arabidopsis homolog of maize CRINKLY 4. Except for ACR4 and CR4 these RLKs carry leucinerich repeats in their extracellular domains and thus encode members of the large LRR-RLK subfamily of RLKs. ACR4 and CR4 feature TNFR-like cysteine-rich repeats and fall into a different family of RLKs. STRUBBELIG is another LRR-RLK gene with a role in tissue morphogenesis of many plant organs. Originally identified in a screen for ovule mutants SUB was shown to be important not just for the initiation and outgrowth of ovule integuments but also for floral organ shape, stem height and shape, leaf shape and root hair patterning. SUB is a member of the small STRUBBELIG RECEPTOR FAMILY /LRRV gene family. Another member, SRF4, affects leaf size while SRF3 plays a role in plant pathogen response and potentially in speciation. For other SRF genes, such as SRF4 or SRF7, a role in cell wall biology was proposed. At the cellular level an important function of SUB relates to the control of cell division planes. Integument initiation relies on oriented cell divisions. Furthermore, division planes of L1 and L2 cells are frequently misoriented in floral meristems of sub mutants. To some extent SUB is also involved in the regulation of cell proliferation, as reduced cell numbers are observed in integuments and stems of sub mutants. SUB signaling appears to be important for the coordination of such cellular behavior across histogenic cell layers. Although SUB is expressed in a broad fashion in floral meristems and young ovules, expression of a functional SUB:EGFP fusion protein to the L1 layer is sufficient to rescue the L2 division plane defects in floral meristems. In addition, SUB:EGFP expression in the distal nucellus of ovule primordia can rescue to a large extent defects in the integuments, tissue that originates from the central chalaza. Thus, it was proposed that SUB acts in a non cellautonomous fashion and mediates inter-cell-layer signaling during floral development. In this respect SUB may relate to BRI1.