Expression Profiling of Genes Associated with Cyanogenesis in Three Cassava Cultivars Containing Varying Levels of Toxic Cyanogens

摘要

Cyanogenic glycosides, linamarin and lotaustralin, are presents in all tissues of Cassava (Manihot esculenta Crantz) except seeds and function as a deterrent for herbivores as well as the translocable form of reduced nitrogen. The genes involved in the cyanogenic pathway [CYP79D1/D2 (EC 1.14.13), linamarase (EC 3.2.1.21), α-hydroxynitrile lyase (HNL, acetone-cyanohydrin lyase. EC 4.1.2.37) and b-cyanoalanine synthase (β-CAS. EC 4.4.1.9] have been identified and partially characterized. Our objective was to identify the differential expression pattern of these genes in leaves and roots of three cassava cultivars with varying levels of cyanogenic glucosides. The results show that the differential ex- pression of the genes between leaves and roots is consistent with leaves being the primary site of synthesize of cyano- genic glucosides, which are then translocated to the roots. In addition, the varietal difference for cyanogenic glucoside levels could be explained in part by the combinatorial effort of the synthesis in the leaves and the linamarase catabolic step in the roots. Cluster analysis suggests a coordinated expression between CYP79D1/D2 and β-CAS genes as well as linamarase and HNL genes, which is in agreement with the spatial separation within a cell of the site of linamarin syn- thesis (vacuolar) and its breakdown to cyanide (cell wall). Furthermore, cluster analysis for cultivar classification using its gene expression profile match with the reported cyanide levels comparatively for the three cultivars. This is the first study that evaluates the transcriptional activities of the genes involved in the cyanogenic glycoside metabolism using a systematic approach.