MicroRNA (miRNA) are short ribonucleic acid (RNA) molecules which have very few nucleotides (an average of 22). MiRNA genes are located in the intergenic regions of the plant genome. They regulate the post-transcriptional expression of proteins in plants and animals. MiRNAs are likely to be involved in most biological processes. 
Aberrant expression of miRNAs has been implicated in numerous disease states, such cancer, heart disease and diseases of the nervous system. They are also linked to plant response to biotic and abiotic stress. MiRNA genes and their target genes maintain a gene regulatory network in plants.
Micro RNAs in Cassava 
Patanun et al. 2012 studied the miRNAs of cassava, identifying 34 miRNA families The mes-miR319b represent the first mirtron demonstrated in cassava. Mirtrons are a type of microRNAs that are located in the introns of the mRNA encoding host genes and were found in Drosophila melanogaster, Caenorhabditis elegans.and mammals.
Patanun and colleagues also described elements relevant to drought stress and plant hormone response in the cassava miRNA genes. These findings may lead to the development of improved plant strains.
Cassava bacterial blight defence system of Manihot 
Cassava (Manihot esculenta) is a staple crop which stores important quantities of starch in its roots. These roots constitute the main source of calories for more than half a billion people around the world, mainly in tropical regions and is used for bioethanol production, animal feed and industrial raw materials. An important disease is the cassava bacterial blight (CBB), caused by gram-negative bacteria Xanthomonas axonopodis pv. manihotis (Xam), and produces crop losses up to 80-100%.
Perez-Quintero et al. 2012 studied the miRNAs in cassava under infection with Xam bacteria. Infection increased the expression of some miRNA families, including the miRNAs linked to defence reactions by activating auxin-responding factors. The authors also note that the infection activated families of miRNAs involved in copper regulation and families targeting disease resistance genes, previously known in Arabidopsis thaliana. The miRNAs are important defence system of cassava against Xam and more studies in this direction may lead to varieties with higher resistance to the disease,
 Tang G: Plant microRNAs: an insight into their gene structures and evolution. Semin Cell Dev Biol. 2010 Oct;21(8):782-9.
 Patanun O, Lertpanyasampatha M, Sojikul P, Viboonjun U, Narangajavana J:Computational Identification of MicroRNAs and Their Targets in Cassava (Manihot esculenta Crantz.). Mol Biotechnol. 2012 Mar 3.
 Perez-Quintero AL, Quintero A, Urrego O, Vanegas P, Lopez C: Bioinformatic identification of cassava miRNAs differentially expressed in response to infection by Xanthomonas axonopodis pv. Manihotis. BMC Plant Biol. 2012 Feb 23;12(1):29.