Involved in the coordination between cell elongation and cellulose synthesis by promoting the expression of genes involved in cell elongation and cellulose synthesis (PubMed:15010620, PubMed:10859181, PubMed:12215501, PubMed:24995569). Acts as a regulator of plasmodesmatal permeability (PubMed:22457425). Mediates abscisic acid (ABA) and sugar responses essential for growth (e.g. seed germination, stomatal regulation and ABA-regulated gene expression) (PubMed:14742875). Required for normal organogenesis by promoting cell elongation, regulating cell differentiation in vascular tissues and maintaining root meristem identity (PubMed:15010620, PubMed:10859181). Regulates crystalline cellulose microfibrils deposition and parallel organization during the elongation phase of the cell (PubMed:12215501). Maybe a glycosyltransferase (PubMed:22457425). Negative factor in light inhibition of hypocotyl elongation through modulating cellulose biosynthesis (PubMed:24995569). The cell membrane subcellular localization first observed (PubMed:12215501) and the punctate pattern within the cytoplasm (PubMed:14742875) could not be confirmed (PubMed:15010620). Expressed at low levels in both light- and dark-grown plants (PubMed:15010620, PubMed:12215501, PubMed:14742875). Accumulates especially in the elongation zone of roots (at protein level) (PubMed:14742875). Expressed in the roots regardless of the light treatment, high levels in the uppermost regions of hypocotyls in darkness, but low levels in light-grown hypocotyls (PubMed:24995569). Down-regulated by light in a phytochrome A-dependent manner, via protein destabilization and subsequent degradation by the 26S proteasome (at protein level). Reduced transcription in light conditions in a HY5-dependent manner. Increased plasmodesmatal permeability leading to an increase in intercellular protein trafficking (PubMed:22457425). Growth-defective due to cellulose deficiency, impaired cell elongation and altered cell division in root meristems, thus leading to stunted plants (PubMed:15010620, PubMed:10859181, PubMed:12215501). When light-grown, dwarf, with very short root and lateral organs (e.g. leaves) extremely reduced in size, as well as abnormal vascular tissues, characterized by twisted vascular bundle and the presence of undifferentiated vascular cells (PubMed:15010620, PubMed:24995569). Accumulation of ectopic lignin, especially in the mature part of the root, of ectopic callose accumulation in hypocotyls, and of ectopic suberin around the vascular bundles in roots and hypocotyls (PubMed:15010620, PubMed:10859181, PubMed:12215501). Photomorphogenesis in the dark, absence of etiolated phenotype, with extremely short hypocotyls, shoot development, and inflorescences and flowers production (PubMed:15010620, PubMed:24995569). Inability to grow in soil (PubMed:15010620, PubMed:14742875). The cell wall is constituted by abnormally randomized microfibrils occluded by a layer of pectins probably due to a defect in the synthesis of crystalline cellulose during the elongation phase of the cell (PubMed:15010620, PubMed:24995569). Abscisic acid- (ABA-) resistant germination associated with defective stomatal regulation, altered ABA-responsive gene expression, delayed flowering, and male sterility (PubMed:14742875). Glucose- (Glc-) dependent growth with impaired Glc sensitivity that normaly induces seedling developmental arrest; Glc reverses partially disruption phenotypes (PubMed:14742875). 'Kobito' means 'dwarf' in Japanese. Belongs to the glycosyltransferase 92 family.