Identification of putative silicon transporters in the low accumulators N. tabacum and S. lycopersicum

Authors: Zellner, Wendy; LEISNER, SCOTT - University Of Toledo

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/1/2013
Publication Date: 7/20/2013
Citation: Zellner, W.L., Leisner, S.M. 2013. Identification of putative silicon transporters in the low accumulators N. tabacum and S. lycopersicum. Abstract. American Society of Plant Biologists Annual Meeting, July 20-24, 2013, Providence, Rhode Island.

Interpretive Summary:

Technical Abstract: Silicon (Si) has long been excluded from the list of essential elements based on a definition developed over 60 years ago. However, how can one deem an element “non-essential” if through millennia of adaptation a fundamental pathway of perception and accumulation leading to molecular changes within the organism still persists? Previous studies using the inducible Si accumulator, N. tabacum, indicated that Si was accumulated in response to a pathogen, likely as a defense mechanism. The ability of the plant to accumulate the element in response to stress, suggests a molecular pathway is involved in the perception and accumulation of Si in the presence of a stressor. To elucidate the second part of this pathway, we set out to identify potential Si transporters in two low-accumulating species N. tabacum and S. lycopersicum. Of the identified tomato major intrinsic proteins, the translated sequence of slNIP2;1 contained the selectivity filter amino acid residues unique to known plant Si transporters. In addition to this sequence, a search of N. tabacum ESTs identified a putative MIP that contained the unique selectivity filter residues indicative of Si transporters. Homology modeling of the translated protein, using the spinach aquaporin as a scaffold, was performed resulting in a predicted structure containing the classical six trans-membrane helices present in all aquaporins. In silico docking experiments with silicic acid suggested that the putative tobacco and tomato Si-transporters showed interaction energies similar to those of known Si transporters. The N. tabacum putative Si transporter expression decreased in response to Si treatment after seven days, similar to the expression profile of the rice Lsi1 transcript. However, the tomato transporter expression remained constant in the presence or absence of Si, mirroring expression of the corn and barley Lsi1-like transcripts. A Xenopus oocyte transport study is currently underway to confirm that the putative tobacco and tomato Si transporters can indeed transport the element. These data support the idea that all plants likely possess the machinery enabling controlled accumulation of Si under specific environmental conditions.