Genetic manipulation of the cell wall composition of sugarcane

[摘要] In order to understand and manipulate carbon flux to sucrose one needs to consider not onlyits biosynthetic pathways, but also the competing sinks for carbon in various parts of theplant and at different stages of development. The cell wall and sucrose is known to be themajor sinks for carbon in young and mature tissues of sugarcane. UDP-Glucose is a centralmetabolite in the synthesis of both sucrose and most of the cell wall polysaccharides(including cellulose, hemicellulose and pectic polymers) and manipulation of the flux intoeither of the cell wall components could therefore cause an increase of flux toward one ormore of the competing sinks. In the present study UDP-Glucose dehydrogenase (UGD)activity was chosen for down regulation as it catalyzes the rate limiting step in thebiosynthesis of the precursors of both hemicellulose and pectin, a major competing sink forassimilated carbon.Transgenic sugarcane lines with repressed UGD activity showed significantly increasedsucrose accumulation in all internodes which was highly correlated with reduced UGDactivity. Sucrose phosphate synthase had increased activation which suggests an alterationin carbon flux toward sucrose.The reduction of carbon flux through UGD was compensated for by an increase in theactivity of the myo-inositol oxygenation pathway (MIOP), an alternative pathway for thesynthesis of cell wall matrix precursors. The increased activity of the MIOP resulted inincreased total uronic acids and pentoses in the cell wall. Total cell wall glucose was alsoincreased which is a further indication of altered carbon metabolism.

[发布机构] Stellenbosch University