Chitosan enhances rice seedling growth via gene expression network between nucleus and chloroplast

Chitosan, a partially deacetylated form of the natural and biodegradable biopolymer chitin, has been used as plant growth promoter in agriculture. The aim of this work was to investigate the growth promoting responses induced by chitosan at the physiological and molecular level in rice (Oryza sativa L.) seedlings. The combination of the degree of deacetylation (DD), molecular weight and concentration of chitosan had differing effects on the rice seedling growth. For the best enhancement, oligomeric chitosan with an 80 % DD applied at 40 mg/L significantly enhanced the vegetative growth, in terms of the leaf and root fresh weights and dry weights of rice seedlings compared to the control. At the proteomics level, of the 352 rice leaf proteins that could be resolved using the Multi Experiment Viewer software, 105 showed a significantly different expression level in rice leaves treated with chitosan compared to the control. Co-expression network analysis revealed nine of these proteins had significant coexpression with other genes from the three main biochemical network systems of photosynthesis, carbohydrate metabolism and cell redox homeostasis. More than 90 % of the genes positively co-expressed with these nine chitosan-responsive proteins were localized in chloroplasts, suggesting that chitosan enhanced the plant growth of rice seedlings via multiple and complex networks between the nucleus and chloroplast.