Tomatoes Are Useful For More Than Just Bruschetta!

In my previous blogs, I have explained my overall goals for my research involving phosphate stress. I hope to learn more about the two main secreted PAPs (12 and 26) found in Arabidopsis and eventually over-express these proteins. However, I recently came across some research with a very similar approach to the issue of declining available phosphate and the need to produce transgenic phosphate-efficient crops.

Dr Gao and her colleagues published a very detailed research paper this past summer in the Plant Soil Journal. Previous studies found a regulatory element, miR399, involved in the phosphate starvation response. The main research focus of this regulatory element has been in tobacco plants. However, Dr Gao wished to evaluate whether miR399s can be over-expressed in tomatoes. From there, they wished to study the phenotypes associated with phosphate stress when this over-expression occurs. 

 

The method section of this research paper begins by covering all of the genetic and molecular biology used to produce an over-expressed miR399 gene. To be honest, most of this information is beyond me. I understand the basics of the screening and the use of the Agrobacterium, then I’m out. Not to say that this section is not well written but this topic is obviously written for a very knowledgeable scientific reader. However, when they start talking about plant growth conditions, I’m in!

They placed the transgenic tomatoes in soil and measured phosphate concentration of tomato shoots. They also used hydroponic growth systems in a low phosphate environment to measure the changes in protons excretion, and APase activity. To test the consumption of organic and insoluble forms of phosphate of these transgenic tomatoes, inositol hexaphosphate-Na (OP, an organic form of phosphate) or AlPO4 (Al-P, an insoluble form of phosphate) was used. 

The results of this research are very well written. On the other hand, the presentation of the results in figures, tables and graphs is very unclear. The figure legends are not always next to the figures, but can be found in odd places with arrows pointing to the appropriate figure. Additionally, the graphs contain patterns to distinguish between the wildtype and transgenic tomatoes. However, they have the first transgenic line as plain and then the second transgenic line and wildtype as a pattern. For anyone doing a quick read of this paper, it makes much more sense to have wildtype in the plain pattern and the two transgenic forms in the distinguishable patterns.  

Well enough about those small details, let’s cover the actual results of this paper. In the transgenic tomato, leaf phosphate concentration increased significantly in soil, and roots had a higher uptake of phosphate (can be seen in Fig. 3 to the right). LePT1, LePT2, LePT4, and LePT5 transcripts were upregulated, causing an over-expression of phosphate transporters. These results can be seen in Table 4 above. The researchers also found an increase in APase activity in transgenic roots, which allowed hydrolysis of organic P. An increase in proton excretion was observed, which allowed for superior dissolution of AlPO4. This dissolution can be seen in Fig. 4 to the left.

They concluded that phosphate concentration in transgenic tomatoes over-expressing ath-miR399 significantly increased in soil. Association of the roots of transgenic tomato over-expressing ath-miR399 also had a higher uptake of phosphate. Their results enhance the understanding of miR399-overexpressing plants that accumulate excess phosphate in shoots. They also rightfully include a suggestion for a future experiment. They thought a good next step would be to study miR399-mediated molecular signaling pathway that upregulates APase activity and proton extrusion. Finally, a paper that looks to the future!

Overall, I really enjoyed this paper. Maybe it was just because they took a similar approach that I am also thinking of taking, but the quality of the paper cannot be denied. Additionally, knowing that an over-expression of genes in Arabidopsis can be translated into other crops, only cements my ideas for PAP26 over-expression.

And I mean come on, we can’t have a world without well-grown tomatoes. Fajitas, Greek salads, Bruschetta all require delicious tomatoes! And I don’t plan on spending a day without any of the afore mentioned treats… do you?

Reference

Gao, N Yanhua, S and Shen, W.  2010. Transgenic tomato over-expressing ath-miR399d has enhanced phosphorus accumulation through increased acid phosphatase and proton secretion as well as phosphate transporters. Plant Soil 334:123–136.