Agriculture Reference
In-Depth Information
collaboration with the Tamas Dalmay laboratory (School of Biological Sciences, UEA, Norwich,
UK) (unpublished data).
Still, the bioinformatic prediction of many hypothetical genes for miRNA targeting raises the
question whether we are dealing with true or instead pseudo targets and can have a strong
implication on our assumptions about the mechanisms of miRNA functioning as they impose
an additional layer of post-transcriptional regulation.
Seitz [152] proposed that many computational identified miRNA targets are indeed pseudo‐
targets that prevent miRNAs from binding their true targets by sequestering them. They would
have the basic features of miRNA targets identified by the target prediction algorithms:
complementarity to miRNAs and phylogenetic conservation but are instead modulators of
miRNA expression.
These pseudotargets occur naturally in plants [145] and animals [146] and were firstly
associated to miRNA regulation of nutrient deprivation but their involvement in other abiotic
stress conditions like water deprivation may also be envisaged.
A 5-year EU FP7 project designated “ABStress - Improving the resistance of legume crops to
combined abiotic and biotic stress” was recently started [153]. This project will study the small
RNAs and epigenetic regulation involved in abiotic and biotic stresses in Legumes using
Medicago truncatula
as a model and it is certainly expected to bring new information about the
complex network of regulatory circuitries in which miRNAs participate.
4. Transgenic approaches to improve abiotic stress resistance
The advance in genetic engineering offers new ways to understand the genetic mechanisms
of stress-related genes and their contribution to the plant performance under stress [154].
However, while a great degree of success has been obtained in the production of herbicide-,
virus- and fungal-resistant plants and plants with fortified nutritional values using transgenic
tools, the same has not been the case in production of abiotic stress-tolerant crops [155]. This
is largely due to the complex genetic mechanisms that govern abiotic stress tolerance. Addi‐
tionally, as previously referred, in natural conditions, crops can suffer from different stress
combinations, at different development stages and during different time periods.
Recently, several reviews were published concerning genetic engineering for abiotic stress
tolerance, most focused in model but also in crop plants (e.g. [156 -161]). Possible targets for
genetic engineering towards abiotic stress in plants are genes belonging to structural and
regulatory categories. They can be modified (for example truncated) and fused to other genetic
components such as signal peptides that direct their expression to specific organelles and/or
reporter genes for early detection in transgenic plants. After the proper cloning of the desired
genes, they are engineered for their expression to be regulated in a time and space context,
using specific promoters. The approach can take into account if it is desirable to have the gene
expression upregulated, by sense overexpression of the transgene, or downregulated, by the
antisense or RNA interference (RNAi) techniques.
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