Light modulated activity of root alkaline/neutral invertase involves the interaction with 14‐3‐3 proteins

Abstract

Summary Alkaline/neutral invertases (A/N‐Invs) are now recognized as essential proteins in plant life. They catalyze the irreversible breakdown of sucrose into glucose and fructose and thus supply the cells with energy as well as signaling molecules. In this study we report on a mechanism that affects the activity of the cytosolic invertase AtCINV1 (At‐A/N‐InvG or AT1G35580). We demonstrate that Ser547 at the extreme C‐terminus of the AtCINV1 protein is a substrate of calcium‐dependent kinases (CPK3 and 21) and that phosphorylation creates a high‐affinity binding site for 14‐3‐3 proteins. The invertase as such has basal activity, but we provide evidence that interaction with 14‐3‐3 proteins enhances its activity. The analysis of three quadruple 14‐3‐3 mutants generated from six T‐DNA insertion mutants of the non‐epsilon family shows both specificity as well as redundancy for this function of 14‐3‐3 proteins. The strong reduction in hexose levels in the roots of one 14‐3‐3 quadruple mutant plant is in line with the activating function of 14‐3‐3 proteins. The physiological relevance of this mechanism that affects A/N‐invertase activity is underscored by the light‐induced activation and is another example of the central role of 14‐3‐3 proteins in mediating dark/light signaling. The nature of the light‐induced signal that travels from the shoot to root and the question whether this signal is transmitted via cytosolic Ca++ changes that activate calcium‐dependent kinases, await further study.

A Member of the 14-3-3 Gene Family in Brachypodium distachyon, BdGF14d, Confers Salt Tolerance in Transgenic Tobacco Plants

“…Further, the expression profiles of the Bd14-3-3 gene family under abiotic stresses and ABA treatment showed isoform-specific up- or down-regulation ( Figure 4 ), thus implying their various roles in the abiotic stress responses of B. distachyon . The crucial roles of the 14-3-3 proteins in the light-signaling pathway have been clarified extensively in Arabidopsis (Sullivan et al, 2009; Gao et al, 2014) and rice (Taoka et al, 2011), and certain light-responsive elements were identified in promoters of the Bd14-3-3s (data not shown). Hence, when these are taken into consideration, up-regulation of the expression levels of the Bd14-3-3s following exposure to light was expected under controlled condition.…”

Comparative Transcriptional Analysis of Loquat Fruit Identifies Major Signal Networks Involved in Fruit Development and Ripening Process

“…For example, 14-3-3 proteins can directly or indirectly interact with SPS to mediate sucrose synthesis. The interaction protected SPS from the attack of proteinase [34]. …”

Properties and functions of calcium‐dependent protein kinases and their relatives inArabidopsis thaliana

“…In particular, the cytosolic invertase AtCINV1, which catabolizes sucrose into fructose and glucose for energy supply in the roots, is stimulated under light in vivo by 14‐3‐3 binding. It was demonstrated that 14‐3‐3 binding required phosphorylation on S547, which was targeted by AtCPK3 in vitro (Gao et al ., ). AtCPK3 also phosphorylates the bifunctional enzyme F2KP (6‐phosphofructo‐2‐kinase/fructose‐2,6‐bisphosphatase) on S220/S303 leading to 14‐3‐3 binding, although the molecular consequences remain unknown (Kulma et al ., ).…”