Researchers at Okayama University in Japan have discovered that the Silicon Efflux Transporter 4 (SIET4) plays a crucial role in facilitating the localization of silicon (Si) in rice leaves. Si accumulation in certain plant species is known to act as a protective mechanism against various stressors, including abiotic and biotic factors. In rice, which can store Si up to 10% of the dry weight of shoots, Si is vital for stable grain production. While the transporters governing Si uptake by roots and root-to-shoot translocation were previously identified, the specific machinery for cell-specific Si deposition in rice leaves remained unknown.
The research team, led by Dr. Jian Feng Ma, conducted functional analyses, including the generation of SIET4 knockout mutants, to understand the role of SIET4 in leaf Si accumulation. They found that SIET4 is a Si transporter constitutively expressed in rice leaves, specifically localized in the distal side of epidermal and bulliform cells. Plants lacking SIET4 displayed inhibited growth and abnormal Si deposition in leaf mesophyll cells, leading to the conclusion that SIET4 is essential for proper Si export from leaf cells to the leaf surface and the healthy growth of the plant.
The discovery challenges the long-standing belief that Si, an abundant element in soil, does not damage plants, showcasing the importance of intricate processes like Si accumulation for plant survival. The findings open avenues for further understanding high Si accumulation in plants, with potential applications in improving the productivity of various crops.