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 - gene or ten genes (- to -) resulted in a similar sensitivity to Cd and Cu toxicity. When subjected to Cu and Cd stress, the - and -- 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 - and -- mutants were significantly higher than those in the wild-type (WT) and --overexpressing line. However, Cu and Cd accumulation in the cell wall was the opposite. Furthermore, we determined lignin accumulation. The overexpressing-- line had a higher lignin accumulation in the shoot and root cell walls than those of the WT, -, and --. The expression of lignin synthesis genes in the --overexpressing line was significantly higher than that in the WT, -, and --. The SOD activity of -, Diaminobe-nzidine (DAB), propidium iodide (PI) staining, and Malondialdehyde (MDA) content determination suggested that - 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 may play a major role in the tandem repeat gene clusters of chromosome 8 under heavy metal stress conditions.