OsGLP8-7 interacts with OsPRX111 to detoxify excess copper in rice.

Lignin is a phenolic biopolymer generated from phenylpropanoid pathway in the secondary cell wall and is required for defense of plants against various stress. Although the fact of stress-induced lignin deposition has been clearly demonstrated, it remains largely elusive how the formation of lignin is promoted under Cu stress. The present study showed that OsGLP8-7, an extracellular glycoprotein of rice (Oryza sativa L.), plays an important function against Cu stress. The loss function of OsGLP8-7 results in Cu sensitivity whereas overexpression of OsGLP8-7 scavenges Cu-induced superoxide anion (O2•-). OsGLP8-7 interacts with apoplastic peroxidase111 (OsPRX111) and elevates OsPRX111 stability when exposed to excess Cu. In OsGLP8-7 overexpressing (OE) lines, the retention of Cu within cell wall limiting Cu uptake into cytoplasm is attributed to the enhanced lignification required for Cu tolerance. Exogenous application of a lignin inhibitor can impair the Cu tolerance of transgenic Arabidopsis lines overexpressing OsGLP8-7. In addition, co-expression of OsGLP8-7 and OsPRX111 genes in tobacco leaves leads to an improved lignin deposition compared to leaves expressing each gene individually or the empty vector. Taken together, our findings provided the convincing evidences that the interaction between OsGLP8-7 and OsPRX111 facilitates effectively lignin polymerization, thereby contributing to Cu tolerance in rice.

OsGLP participates in the regulation of lignin synthesis and deposition in rice against copper and cadmium toxicity.

Copper (Cu) and cadmium (Cd) are common heavy metal pollutants. When Cd and excessive Cu accumulate in plants, plant growth is reduced. Our previous study showed that Germin-like proteins (GLPs), which exist in tandem on chromosomes, are a class of soluble glycoproteins that respond to Cu stress. In this study, hydroponic cultures were carried out to investigate the effect of GLP on Cd and Cu tolerance and accumulation in rice. The results showed that knockout of a single OsGLP8-2 gene or ten OsGLP genes (OsGLP8-2 to OsGLP8-11) resulted in a similar sensitivity to Cd and Cu toxicity. When subjected to Cu and Cd stress, the glp8-2 and glp8-(2-11) mutants displayed a more sensitive phenotype based on the plant height, root length, and dry biomass of the rice seedlings. Correspondingly, Cu and Cd concentrations in the glp8-2 and glp8-(2-11) mutants were significantly higher than those in the wild-type (WT) and OsGLP8-2-overexpressing line. However, Cu and Cd accumulation in the cell wall was the opposite. Furthermore, we determined lignin accumulation. The overexpressing-OsGLP8-2 line had a higher lignin accumulation in the shoot and root cell walls than those of the WT, glp8-2, and glp8-(2-11). The expression of lignin synthesis genes in the OsGLP8-2-overexpressing line was significantly higher than that in the WT, glp8-2, and glp8-(2-11). The SOD activity of OsGLP8-2, Diaminobe-nzidine (DAB), propidium iodide (PI) staining, and Malondialdehyde (MDA) content determination suggested that OsGLP8-2 is involved in heavy metal-induced antioxidant defense in rice. Our findings clearly suggest that OsGLPs participate in responses to heavy metal stress by lignin deposition and antioxidant defense capacity in rice, and OsGLP8-2 may play a major role in the tandem repeat gene clusters of chromosome 8 under heavy metal stress conditions.