The phytolongin AtPhyl2.1 is involved in cell plate formation and root development

SNAREs are critical elements of the membrane trafficking machinery with a wide variety of functionality across this family of proteins. Phytolongins are a recently identified subfamily of longins which possess the typical longin domain but lack a SNARE motif. Phytolongins have an ubiquitous tissue expression in Arabidopsis and are distributed throughout the secretory pathway. We focused on Phytolongin 2.1 (PHYL2.1) which localizes to the endoplasmic reticulum, and observed a strong root growth phenotype in the loss-of-function Atphyl2 . 1-1 mutant. We demonstrate that whilst cell elongation efficiency was not affected in the mutant, cell division was significantly reduced. The resulting decrease in root length in the Atphyl2 . 1-1 mutant is explained by a smaller number of cells which then elongate to enable root growth. Root apical meristem architecture of Atphyl2 . 1-1 and another mutant Atphyl2 . 1-2 was disturbed and distances from the root quiescent center to the transition zone and the first areas of mis-organized cells were affected in both mutants. Investigation of the SNARE AtKNOLLE revealed significant perturbation of Atphyl2 . 1-1 cell plate formation in the mis-organised areas. Our results provide a first characterization of the phytolongin AtPHYL2.1 which appears involved in root cell plate formation, root cell division and therefore root development. Highlight The phytolongin AtPHYL2.1 significantly affects the efficiency of cell plate formation and root development in Arabidopsis thaliana .