The differential partition of copper in cell wall and symplastic space contributes to the natural variation of copper toxicity tolerance in rice

Aims: Copper (Cu) is an essential microelement for plants but it's toxic at elevated concentration. The natural variation, physiological and genetic basis of rice in response to Cu toxicity was revealed herein. Methods: The genotypic variation of rice sensitivity to excess Cu was investigated by using a natural collection of 183 rice accessions, Cu deposition in the whole root tips and the cell fractions of Cu-tolerant DF82, DF93 and sensitive ZH11 was determined, the expression levels of the potential genes related to Cu transport and cell wall modeling were compared.Results: The sensitivity of rice in response to excessive Cu showed large variation with a relative root elongation at 18 ~ 107%. A slightly higher Cu concentrations in the root tips of DF93 than that of DF82 and ZH11 however, more Cu was deposited in the root cell wall and extremely lower Cu was accumulated in the symplastic space of the DF82 and DF93. The expression of OsCOPT1 was reduced in the root tips of DF93, while the transcriptions of OsCOPT7 and OsHMA5 were more abundant. In addition, the expression of several genes encoding the enzymes and receptor kinases potentially involved in cell wall remodeling was regulated by excessive level of Cu, and certain members displayed varied expression pattern in DF93 and ZH11. Conclusions: The differential partition of Cu in cell wall and symplastic space contributes to the natural variation of Cu tolerance in rice, which is likely attributed to the differentially expressed genes responsible for Cu transport and cell wall remodeling.