TITLE:
Expression Profiling of Genes Associated with Cyanogenesis in Three Cassava Cultivars Containing Varying Levels of Toxic Cyanogens
AUTHORS:
Morgan Echeverry-Solarte, Victor Ocasio-Ramirez, Annete Figueroa, Eduardo González, Dimuth Siritunga
KEYWORDS:
Cassava; Cyanogenic Glucoside; Gene Expression; Real Time PCR
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.4 No.7,
July
17,
2013
ABSTRACT:
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.