Sunday, 20 May 2012

‘Perfect’ Shape of Leaves and Roots?

By Ann Nie Kong (42813358)


Figure 1.Arabidopsis thaliana (, 2012)
The beauty of nature is partly created from the uniformity of roots, stems and leaves of plants, in which these three major organ groups are also the main component of their survival. Based on the two of the three types of organs (leaves and side roots), scientists have now discovered how plants achieve these aesthetics proportions and develop these ‘perfectly-shaped’ organs; by a small regulatory RNA (siRNA) molecules which is the trans-acting short interfering RNAs (ta-siRNAs).

Plant organs such as leaves and roots are characterized and classified according to their structure, shape, characteristics and functions. The formation of these main organs is dependent on proteins which are required to allow cell division and development of shapes and characteristics in cells. This basically follows the basic principles of transcription and translation of gene expression for the making of the unique proteins.  RNA interference occurs in the purpose of regulating gene expression by the production of small interfering RNAs (siRNAs) that bind to messenger RNA (Campbell et al. 2008). This will cause the mRNAs to be broken down so that there will be no further protein production (Campbell et al. 2008). Small interfering RNAs (siRNAs) are known to control a wide range of growth and developmental processes in plants and animals. In this discovery, scientists used Arabidopsis thaliana, a small flowering plant in the mustard family that has a very high growing rate (Page & Grossniklaus 2002).

Figure 2.Comparison between a normal mouse-ear cress (Arabidopsis) plant (on the left), and a plant with abnormal leaf structure. The abnormal leaf structure indicates that the ta-siRNA formation is blocked. (Jouannet et al 2012)

Trans-acting small interfering RNAs (ta-siRNAs) are a type of siRNA unique in plants is known by researchers which can optimize the formation of leaves and growth of roots (Adenot et al. 2006). This is achieved by interfering of the siRNA in the production of the specific proteins (Campbell et al. 2008). 

Where exactly in the plant cell are the ta-siRNAs found?

         The formation of ta-siRNAs  requires a protein known as ARGONAUTE7 (AGO7) that cuts longer RNA molecules. This protein is located in siRNA bodies contained in the cytoplasm of the cells (Jouannet et al. 2012), There is a complex of other molecules such as enzymes besides AGO7 required to form ta-siRNAs as well and are also found in the siRNA bodies. This findings therefore confirms that this is the site for the formation of the siRNAs. This is also supported by the complications arising in the development of the plant organs when the AGO7 is removed from the siRNA bodies, which indicates that the AGO7 could not function properly outside of the siRNA  bodies (Jouannet et al. 2012). 

Interestingly, these specific siRNA bodies also host viruses. In contrast, plants use siRNAs as a natural defense against virus infections (Campbell et al. 2008). In addition, there is a strong relation between the siRNA bodies to the cytoplasm and membranes in which many processes of proteins such as transportation and secretion take place. The importance of the AGO7 in siRNA bodies in the network membranes thus reveals that the role of membranes in biogenesis of RNA still remains unknown up until now. However, the findings suggested that the formation of siRNA will be able to only occur in specific sites of the cell (Jouannet et al. 2012).

Figure 3.Arabidopsis plants. (VasiliyKoval,Fotolia, 2012)

    The targeted control of this RNA could suggest further assessment of biodiversity and endogenous plant counterpart. Further implications for agriculture and understanding plant evolution could be suggested as well.


Adenot, X, Elmayan, T, Lauressergues, D, Boutet, S, Bouche, N, Gasciolli, V & Vaucheret, H 2006, DRB4-Dependent TAS3 trans-Acting siRNAs Control Leaf Morphology through AGO7’, Current Biology, vol. 50, no. 2, pp. 49-52.

Campbell, NA, Reece, JB & Meyers, N 2008, Biology, 8th Edition, Pearson Education, Inc, Australia.

Jouannet, V, Moreno, AB, Elmayan, T,  Vaucheret, H,  Crespi, MD, Maizel, A 2012, ‘Cytoplasmic Arabidopsis AGO7 accumulates in membrane-associated siRNA bodies and is required for ta-siRNA biogenesis’,The EMBO Journal, viewed 19 March 2012, <>. 

Page, DR & Grossniklaus, U 2002, 'The art and design of genetics screens: Arabidopsis thaliana', Nature Review Genetics, vol. 3, no. 1, pp. 49-52.

ScienceDaily 2012, Hotspots forBiogenesis of Small RNA Molecules in Plant Cells Dicovered, viewed 16 March 2012, <>.


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