Claening up (or remediating) soils and improving plant nutritional quality

Understanding the natural process of metal accumulation and storing could eventually allow for the transferal of these characteristics to plants which are lacking in them. To what gain? The ability to absorb metals is of double interest: phytoremediation and biofortification. Phytoremediation consists of decontaminating soils, naturally polluted or contaminated through human activity, through the use of plants. To do this, the ideal thing would be to transfer A.halleri’s abilities to plants which grow very rapidly and deeply into the soil.

As for biofortification, it involves research which aims at producing plant varieties enriched in nutriments (notably in iron, zinc and vitamin A) in order to improve their nutritional quality. This process will therefore allow food to be improved, and thus human health at the same time. An opportunity which is not negligible when one knows that, for example, 30% to 40% of the world population shows signs of zinc deficiency.

Finally, discovering how metallophyte plants absorb and store metals in their leaves could equally lead to the elimination of toxic metals, for plants and humans. By way of example: tobacco accumulates a lot of cadmium in its leaves. Thus, a smoker absorbs twice the amount of this metal than a non smoker.

Arabidopsis halleri 's

In order to verify the HMA4 gene’s crucial role in A.halleri’s accumulation of zinc and cadmium, Marc Hanikenne and his colleagues used the technique known as RNA interference. ‘This technique consists of creating an interfering RNA which is looped and complementary to the messenger RNA produced naturally by the cell to translate the gene into proteins’ explains the researcher. ‘Once introduced into the cell the expression of this looped RNA causes the destruction, by the cell, of the target gene’s messenger RNA. Its expression is consequently inhibited’, he specifies.

Thanks to this technique the scientists were able to reduce the expression of HMA4 in A.halleri by 90%. The result: A.halleri no longer tolerated or accumulated metals. This confirmed the importance of the HMA4 gene in the plant's hyper-tolerance and hyper-accummulation mechanisms.

The second stage of this study consisted in elucidating the reasons for the over-expression of this gene in A.halleri, as HMA4 is 50 times more expressed in it than in mouse ear cress.

In comparing the genome of these two ‘sisters’, Marc Hanikenne and his colleagues discovered that the famous gene was triplicated in A.halleri. ‘After sequencing 300,000 pairs of A.halleri’s genome bases we observed that it possessed 3 copies of the HMA4 gene, which followed each other in tandem, whereas A.thaliana has just a single copy,’ the biologist points out.

This triplication thus explains why the gene could be 3 times more expressed in Arabidopsis halleri. But what other wheeze has the plant come up with to reach a level of expression so much higher than in its sibling?