Posttranslational Elevation of Cell Wall Invertase Activity by Silencing Its Inhibitor in Tomato Delays Leaf Senescence and Increases Seed Weight and Fruit Hexose Level  

Abstract

Invertase plays multiple pivotal roles in plant development. Thus, its activity must be tightly regulated in vivo. Emerging evidence suggests that a group of small proteins that inhibit invertase activity in vitro appears to exist in a wide variety of plants. However, little is known regarding their roles in planta. Here, we examined the function of INVINH1, a putative invertase inhibitor, in tomato (Solanum lycopersicum). Expression of a INVINH1:green fluorescent protein fusion revealed its apoplasmic localization. Ectopic overexpression of INVINH1 in Arabidopsis thaliana specifically reduced cell wall invertase activity. By contrast, silencing its expression in tomato significantly increased the activity of cell wall invertase without altering activities of cytoplasmic and vacuolar invertases. Elevation of cell wall invertase activity in RNA interference transgenic tomato led to (1) a prolonged leaf life span involving in a blockage of abscisic acid-induced senescence and (2) an increase in seed weight and fruit hexose level, which is likely achieved through enhanced sucrose hydrolysis in the apoplasm of the fruit vasculature. This assertion is based on (1) coexpression of INVINH1 and a fruit-specific cell wall invertase Lin5 in phloem parenchyma cells of young fruit, including the placenta regions connecting developing seeds; (2) a physical interaction between INVINH1 and Lin5 in vivo; and (3) a symplasmic discontinuity at the interface between placenta and seeds. Together, the results demonstrate that INVINH1 encodes a protein that specifically inhibits the activity of cell wall invertase and regulates leaf senescence and seed and fruit development in tomato by limiting the invertase activity in planta.

New Insights into Roles of Cell Wall Invertase in Early Seed Development Revealed by Comprehensive Spatial and Temporal Expression Patterns of GhCWIN1 in Cotton

“…Consistently, high CWIN activities correlate with high Glc level and mitotic activity in faba bean embryo (Weber et al, 1996(Weber et al, , 1997 and maize endosperm (Cheng et al, 1996;Vilhar et al, 2002). Loss of CWIN expression reduces seed filling in maize (Cheng et al, 1996) and rice , whereas elevation of CWIN activity by silencing its inhibitor increases seed size in tomato (Jin et al, 2009), demonstrating the critical role of CWIN in seed development.…”

“…Extensive studies have shown essential roles of CWIN in seed filling, probably through regulating Suc unloading and the establishment and maintenance of sink strength (Cheng et al, 1996;Weber et al, 1996;Wang et al, 2008;Jin et al, 2009;Zanor et al, 2009). However, it remains largely unknown how CWIN exerts its regulation early in seed development .…”

“…In planta CWIN activity is capped by its inhibitory protein (Jin et al, 2009 Fig. S3), GhINH1 was constantly but weakly expressed in 5-DAA seed and 10-to 15-DAA filial tissues, suggesting that CWIN activity may be limited by GhINH1 during seed development.…”

Role of cis-12-Oxo-Phytodienoic Acid in Tomato Embryo Development

“…In tomato flowers the LIN5-dependent generation of hexoses (Zanor et al, 2009) is regulated posttranslationally by a LIN5-specific inhibitor protein INVINH1, which gene is coexpressed with LIN5 within the gynoecia (Jin et al, 2009). Silencing of INVINH1 allowed extra invertase activity that led to more hexoses being available for developing seeds and was followed by an increase in seed weight and size (Jin et al, 2009).…”

“…Silencing of INVINH1 allowed extra invertase activity that led to more hexoses being available for developing seeds and was followed by an increase in seed weight and size (Jin et al, 2009). Interestingly, such invertase inhibitors are downregulated by OPDA (Taki et al, 2005).…”