Characterisation and role of <i>Isoamylase1 (Meisa1</i>) gene in cassava

Abstract

The current concept for starch biosynthesis in plants is that amylopectin, the major fraction of starch, is synthesised by the concerted actions of ADP-Glc pyrophosphorylase (AGPase), soluble starch synthase (SS), starch-branching enzyme (BE), and starch-debranching enzyme (DBE). We have isolated a cDNA clone of
Isoamylase1 gene, a member of DBE family from cassava (Manihot esculenta Crantz) storage root. The cloned cDNA fragment sequence (764 bp) showed high identity of 90% to Rcisa1, and 81% identity to Psisa1, Stisa1 and Atisa1. The deduced protein sequence showed highest (92%) identity with RCISA1. The comparative sequence analysis confirmed the cloned fragment to be M. esculenta isoamylase1 gene (Meisa1; accession number GU229751). Genomic analysis revealed occurrence of at least two copies of the Meisa1 gene. Highest
Meisa1 transcript expression levels were detected in fibrous root followed by in the stem and least detected in the leaf and petiole. Analysis of the temporal expression pattern in the storage root showed initial and maximum expression at 90 days after planting (DAP), and declined thereafter to undetectable levels by 180 DAP. The results implicate a major role of Meisa1 in storage root differentiation and early starch granule initiation.