A Tonoplast P3B-ATPase Mediates Fusion of Two Types of Vacuoles in Petal Cells

Abstract

Summary: It is known that plant cells can contain multiple distinct vacuoles; however, the abundance of multivacuolar cells and the mechanisms underlying vacuolar differentiation and communication among different types of vacuoles remain unknown. PH1 and PH5 are tonoplast P-ATPases that form a heteromeric pump that hyper-acidifies the central vacuole (CV) of epidermal cells in petunia petals. Here, we show that the sorting of this pump and other vacuolar proteins to the CV involves transit through small vacuoles: vacuolinos. Vacuolino formation is controlled by transcription factors regulating pigment synthesis and transcription of PH1 and PH5. Trafficking of proteins from vacuolinos to the central vacuole is impaired by misexpression of vacuolar SNAREs as well as mutants for the PH1 component of the PH1-PH5 pump. The finding that PH1-PH5 and these SNAREs interact strongly suggests that structural tonoplast proteins can act as tethering factors in the recognition of different vacuolar types. : Faraco et al. describe vacuolinos, small vacuoles coexisting with the CV in petal epidermal cells. Vacuolino formation is co-regulated with pigmentation and vacuolar acidification. Vacuolar proteins traffic through vacuolinos, and their delivery to the CV requires balanced expression of vacuolar SNAREs and P-ATPases interacting on the tonoplast. Keywords: multiple vacuoles, membrane fusion, SNARE complex, membrane recognition, tethering factors