Expression of a stress-responsive gene cluster for mycosporine-2-glycine confers oxidative stress tolerance in Synechococcus elongatus PCC7942

Abstract

Mycosporine-like amino acids (MAAs) are a class of well-documented UV-screening compounds produced by taxonomically diverse organisms. Extensive studies revealed that a rare MAA, mycosporine-2-glycine (M2G), possesses unique biological activities and functions. M2G is not only a potent antioxidant, but also suppresses protein glycation in vitro, and production of inflammatory mediators in RAW 264.7 macrophages. The present study evaluates vital functions of M2G in a heterologous expression system. The stress-sensitive fresh water cyanobacterium Synechococcus elongatus PCC7942, carrying a M2G biosynthetic gene cluster, was generated. The M2G-expressing cells were more tolerant to H2O2-induced oxidative stress than the wild type, with a half-maximal inhibitory concentration (IC50) value of 2.3 ± 0.06 mM. Transcriptional analysis revealed that all M2G biosynthetic genes were highly up-regulated under oxidative stress. Further, expression of vital genes in the cellular antioxidant defense system, including sodB, cat and tpxA were modulated and up-regulated. Elevated M2G was detected under oxidative stress as well as salt stress treatments. This study provides insight into the molecular and cellular effects of the M2G biosynthetic gene cluster, contributing to understanding of the mechanism behind physiological plasticity under this heterologous expression system.