Evidence That High Activity of Vacuolar Invertase Is Required for Cotton Fiber and Arabidopsis Root Elongation through Osmotic Dependent and Independent Pathways, Respectively      

Abstract

Vacuolar invertase (VIN) has long been considered as a major player in cell expansion. However, direct evidence for this view is lacking due, in part, to the complexity of multicellular plant tissues. Here, we used cotton (Gossypium spp.) fibers, fast-growing single-celled seed trichomes, to address this issue. VIN activity in elongating fibers was approximately 4-6-fold higher than that in leaves, stems, and roots. It was undetectable in fiberless cotton seed epidermis but became evident in initiating fibers and remained high during their fast elongation and dropped when elongation slowed. Furthermore, a genotype with faster fiber elongation had significantly higher fiber VIN activity and hexose levels than a slow-elongating genotype. By contrast, cell wall or cytoplasmic invertase activities did not show correlation with fiber elongation. To unravel the molecular basis of VIN-mediated fiber elongation, we cloned GhVIN1, which displayed VIN sequence features and localized to the vacuole. Once introduced to Arabidopsis (Arabidopsis thaliana), GhVIN1 complemented the short-root phenotype of a VIN T-DNA mutant and enhanced the elongation of root cells in the wild type. This demonstrates that GhVIN1 functions as VIN in vivo. In cotton fiber, GhVIN1 expression level matched closely with VIN activity and fiber elongation rate. Indeed, transformation of cotton fiber with GhVIN1 RNA interference or overexpression constructs reduced or enhanced fiber elongation, respectively. Together, these analyses provide evidence on the role of VIN in cotton fiber elongation mediated by GhVIN1. Based on the relative contributions of sugars to sap osmolality in cotton fiber and Arabidopsis root, we conclude that VIN regulates their elongation in an osmotic dependent and independent manner, respectively.

Increase in Invaginated Vacuolar Membrane Structure Caused by Plant Cell Expansion by Genotoxic Stress Induced by DNA Double-Strand Breaks

“…Cells in the elongation zone do not divide but expand with endoreduplication, which refers to multiple DNA replication without chromosome segregation . The cell expansion in the elongation zone mainly depends on the relaxation of the cell wall matrix and the expansion of vacuoles (Wang et al 2010). Plant cell expansion largely depends on vacuole development.…”

Unraveling mechanisms of cell expansion linking solute transport, metabolism, plasmodesmtal gating and cell wall dynamics

“…13 In elongating fibers, of sucrose. 12 While collective expression level of GhSus gene members appears to be strong throughout the fiber elongation period 15 ( Fig. 1), GhVIN1, a major vacuolar invertase in cotton fiber, shows evidently higher expression level early in fiber elongation (0-10 DAA) matching high VIN activity observed in this stage.…”

“…1), GhVIN1, a major vacuolar invertase in cotton fiber, shows evidently higher expression level early in fiber elongation (0-10 DAA) matching high VIN activity observed in this stage. 12 Transgenic analyses revealed that suppression of GhSus expression reduced fiber length and cellulose content 10 and silencing GhVIN1 decreases fiber elongation. 12 These findings indicate that (1) GhSus play roles in both fiber elongation and cellulose biosynthesis through osmotic regulation and supplying UDPglucose as substrate for cellulose production and hexoses for generation of ATP as an energy source for a variety of transport and metabolic processes (2) GhVIN1 appears to be more specifically required for the formation and enlargement of the central vacuole, pivotal for early fiber elongation (see below).…”

“…Once taken up into the fiber cells, sucrose could be degraded into UDPglucose and fructose by sucrose synthesis (GhSus) in the cytoplasm 10 or hydrolyzed by acid invertase into glucose and fructose in the vacuole, thus doubling the osmotic contribution GhSUT1, GhKT1, GhEXP1 are genes encoding sucrose and K + transporter and expansin, respectively; 5 GhSus: sucrose synthase genes; 10,19 GhVIN1: vacuolar invertase gene; 12 GhPIPs and TIPs encode plasma membrane and tonoplast intrinsic proteins, respectively (Ashley J, Patrick Jw, Ruan YL, unpublished data); GhPEPC 1 and 2, and GhGluc1 are genes encoding phosphoenolpyruvate carboxylase 11 and β1, 3-glucanase, 9 respectively. PD: plasmodesmata.…”

“…10,11 However, little is known how osmotically active solutes are accumulated in the vacuole driving the influx of water for cell expansion. In this context, the recent discovery on the important role of vacuolar invertase (VIN) in cotton fiber and Arabidopsis root elongation 12 represents a major advance in our understanding of mechanisms controlling plant cell expansion. Here, we provide an assessment on our current understanding on the coordinated action of multiple pathways regulating fiber elongation and discuss the underlying implications and future directions in our effort to elucidate the molecular and cellular basis of cell expansion, a key component for plant cell development and realization of crop yield.…”