Pectin Methylesterases Enhance Root Cell Wall Phosphorus Remobilization in Rice

Pectin contributes greatly to cell wall phosphorus (P) remobilization. However, it is currently unclear whether the methylesterification degree of the pectin, which is related to the activity of pectin methylesterases (PMEs), is also involved in this process. Here, we demonstrated that elevated PME activity can facilitate the remobilization of P deposited in the cell wall. P-deficient conditions resulted in the reduction of root cell wall P content. This reduction was more pronounced in Nipponbare than in Kasalath, in company with a significant increment of the PME activity, indicating a possible relationship between elevated PME activity and cell wall P remobilization. This hypothesis was supported by in vitro experiments, as pectin with lower methylesterification degree had higher ability to release inorganic P (Pi) from insoluble FePO4. Furthermore, among the 35 OsPME members in rice, only the expression of OsPME14 showed a relationship with PME activity. In addition, transgenic rice lines overexpressing OsPME14 had increased PME activity, released more P from the root cell wall, and more resistant to P deficiency. In conclusion, PMEs enhance P remobilization in P-starved rice by increasing PME activity in Nipponbare, which in turn helps to remobilize P from the cell wall, and thus makes more available P.