Enhancement of saccharification yields from rice straw

We have been studying saccharification yields from rice straws with two strategies.

(1) Senescence-specific expression cellulase

We assumed that if cellulase is expressed during rice growth, cracks will be introduced into cell wall, and such cell wall will be easily degraded by cell wall-degrading enzymes, because they will reach inside of the cell wall through cracks. To this end, we generated transgenic rice plants that constitutively expressed cellulase, and found that the overexpression of cellulase enhanced saccharification yields from rice straws, but development of panicle was also affected, which resulted in sterility. To overcome this problem, we used senescence-specific promoter in stead of a constitutive promoter to avoid the expression of cellulase during panicle development. We could successfully enhance saccharification yields without any penalties. Further enhancement of saccharification yields by expressing cellulase is underway.

(2) Identification of a gene that enhances saccharification yields

We found that saccharification yields from rice straws are different among rice cultivars, and Kasalath (an indica cultivar) shows high saccharification yields and Koshihikari (a Japonica cultivar) shows low saccharification yields (Fig 1). We have been searching a high saccharification gene from Kasalath, and we identified the gene on chromosome 3. Molecular cloning of the gene is underway.