Vacuolar sucrose homeostasis is critical for development, seed properties and survival of dark phases of Arabidopsis

Abstract

Although we know that most of the cellular sucrose is present in the cytosol and vacuole, our knowledge on the impact of this sucrose compartmentation on plant properties is still fragmentary. Here we attempted to alter the intracellular sucrose compartmentation of Arabidopsis mesophyll cells by either, overexpression of the vacuolar sucrose loader BvTST2.1 or by generation of mutants with decreased vacuolar invertase activity (amiR vi1-2). Surprisingly, BvTST2.1 overexpression led to increased monosaccharide levels in leaves, while sucrose remained constant. Latter observation allows the conclusion, that vacuolar invertase activity in mesophyll vacuoles exceeds sucrose uptake in Arabidopsis, which gained independent support by analyses on tobacco leaves transiently overexpressing BvTST2.1 and the invertase inhibitor NbVIF. However, we observed strongly increased sucrose levels in leaf extracts from independent amiR vi1-2 lines and non-aqueous fractionations confirmed that sucrose accumulation in corresponding vacuoles. amiR vi1-2 lines exhibited impaired early development and decreased weight of seeds. When germinated in the dark, mutant seedlings showed problems to convert sucrose into monosaccharides. Cold temperatures induced marked downregulation of the expression of both VI genes, while frost tolerance of amiR vi1-2 mutants was similar to WT indicating that increased vacuolar sucrose levels fully compensate for low monosaccharide concentrations. HighlightVacuolar sucrose accumulation in Arabidopsis is limited by high invertase activity and disturbed vacuolar sucrose homeostasis impairs plant germination, development, seed properties and survival under darkness.