Improvement of cell wall digestibility in tall fescue by Oryza sativa SECONDARY WALL NAC DOMAIN PROTEIN2 chimeric repressor
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Forage digestibility is one of the most important factors in livestock performance. As grasses grow and mature, dry matter increases but they become fibrous with secondary cell wall deposition and lignification of sclerenchyma cells, and forage quality drops. In rice (Oryza sativa), the SECONDARY WALL NAC DOMAIN PROTEIN2 fused with the modified EAR-like motif repression domain (OsSWN2-SRDX) reduces secondary cell wall thickening in sclerenchyma cells. We introduced OsSWN2-SRDX under the control of the OsSWN1 promoter into tall fescue (Festuca arundinacea Schreb.) to increase cell wall digestibility. Of 23 transgenic plants expressing OsSWN2-SRDX, nine had brittle internodes that were easily broken by bending. Their secondary cell walls were significantly thinner than those of the wild type in interfascicular fibers of internodes and in cortical fiber cells between leaf epidermal cells and vascular bundles. The dry matter digestibility increased by 11.8% in stems and by 6.8% in leaves compared with the wild type, and therefore forage quality was improved. In stem interfascicular fibers, acid detergent fiber and acid insoluble lignin were greatly reduced. Thus, the reduction of indigestible fiber composed of cellulose and lignin increased the degradability of sclerenchyma cell walls. OsSWN2-SRDX plants offer great potential in the genetic improvement of forage digestibility.
KeywordsForage digestibility OsSWN2 Secondary cell wall Tall fescue
We thank Ms. Aeni Hosaka, Ms. Kaori Mogi, Ms. Miyuki Sato, and Ms. Hitomi Takaishi for technical assistance. This work was supported by the Research and Development Program for New Bio-industry Initiatives from the Bio-oriented Technology Research Advancement Institution of Japan and the Advanced Low Carbon Technology Research and Development Program (ALCA) from Japan Science and Technology Agency (JST).
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