Abstract

Production and utilization of cassava (Manihot esculenta) is significantly constrained by pests, diseases, poor yields and low nutritional content. Various approaches are currently being applied to mitigate these constraints. However, an aspect of plant developmental genetics little known in cassava is the role that microRNAs (miRNAs) play in gene regulation. miRNAs are 20 - 24 nucleotide long non-protein-coding RNAs that play important roles in post-transcriptional gene silencing in many organisms. Thorough understanding of the mechanisms involved in miRNAs mediated post-transcriptional gene regulation will have implications for crop production improvement. The potential of miRNAs for cassava improvement and also some data obtained on cassava miRNAs using comparative genomics analysis have been briefly discussed. 17 miRNA families and target genes in cassava that are also conserved in other plant species have been revealed. However, the ESTs representing seven of these miRNA families produced foldbacks that show more than 3 nucleotides not involved in canonical base pairing within a loop or bulge in the mature miRNA: RNA* dimer, thus were not considered miRNA secondary structures. Consistent with previous reports, majority of the target genes identified are transcription factors. Other targets appear to play roles in diverse physiological processes. Furthermore, a detailed description and insight into some of the current bioinformatic resources and approaches applicable to cassava have been discussed. Such information will further enhance the rapid discovery and analysis of more novel miRNAs in cassava towards its improvement. 

Key words: Cassava, microRNAs, target genes, improvement, characterization.

Abbreviation

ESTs, Expressed sequence tag; HYL1, hyponastic leaves; siRNAs, short interfering RNAs; miRNA, microRNA; miRISC, miRNA-induced silencing complex; AGO, argonaute; CIAT, International Centre for Tropical Agriculture; CMD, cassava mosaic disease; ILTAB, International Laboratory for Tropical Agricultural Biotechnology; BNARI, Biotechnology and Nuclear Agriculture Research Institute; IAEA, International Atomic Energy Agency; PMRD, plant miRNA database; GSS, genome survey sequences; MFE, minimum fold energy; MFEI, minimal fold energy index; AMFE, adjusted minimal fold energy; TAIR, arabidopsis information resource; PCR, polymerase chain reaction; RT-PCR, reverse transcription-PCR; qRT-PCR, quantitative real-time PCR; SBP, squamosa promoter binding protein.