Herbicide MCPA regulates photosynthesis by repressing gene expression in a cyanobacterium Nostoc muscorum MEG 1: A molecular interaction study

Abstract

The goal of this study was to determine how the herbicide MCPA interacts/binds to two vital proteins of the electron transport system of PS II and photosynthesis in the cyanobacterium Nostoc muscorum Meg 1, as well as how the MCPA affects and regulates the photosynthetic activity of the organism at the molecular level by examining the gene expression of some key proteins involved in the electron transport chain and carbohydrate production in the Calvin cycle. A molecular docking study revealed that MCPA forms hydrogen bonding with amino acid residues in both the proteins (RuBisCO and D1 protein). TEM study revealed that at 20 ppm MCPA exposure, no significant changes in cellular structure were observed. However, increasing concentrations of MCPA (40 and 80 ppm) caused damage to the cyanobacterium's ultrastructure. Seven days’ exposure to herbicide MCPA (20, 40, and 80 ppm) affects the photo-pigment contents, though at 20 and 40 ppm there was a slight increase in the concentration of carotenoid. It also negatively affects the water-splitting activity, PSII, RuBisCO content, and carbohydrate concentration, resulting in decreased organism biomass. The RT-PCR analysis of D1 protein and RuBisCO mRNA levels revealed a significant decrease in content due to herbicide MCPA exposure. Our finding indicates that up to 20 ppm exposure, the herbicide MCPA does not affect the organism dilapidated in all the parameters studied. However, above that dose (40 and 80 ppm), all the parameters studied experienced a substantial negative effect which may lead to the membrane distortion, cellular deterioration, and apoptosis of the cells as seen under the TEM.