Tomato Xylem Sap Protein XSP10

Tomato xylem sap protein XSP10 is required for full susceptibility to Fusarium wilt disease," by Vladimir Krasikov is a characterization of the protein XSP10. XSP10 is a highly abundant xylem sap protein found in tomato with unknown function that is similar to other plant lipid transfer proteins (LTPs). LTPs are able to bind lipids and other hydrophobic molecules and sometimes play a role in plant disease resistance. The amount of XSP10 in the xylem sap has been found to decrease when the plant is infected with Fusarium oxysporum f.sp.

lycopersici (Fol). This protein could be significant in tomato plant resistance to Fol infection. The research in this paper seeks to shed more light on the protein XSP10. The main conclusions of this paper are that the protein XSP10 does have affinity for saturated fatty acids (FA) and that XSP10-silenced tomato plants do not fully develop symptoms of Fol infection. FA affinity was determined with a fluorescent probe called 2-p-toluidinonaphthalene6-sulphonate (TNS). TNS binding is a common assay for determining FA affinity.

TNS is highly fluorescent when bound to the hydrophobic cavity of a protein. If it is displaced by another FA then the fluorescence decreases. In this study it was found that unsaturated FAs were not successful at displacing TNS. Saturated FAs were able to displace TNS. Decreases ranging from 22-35% were seen with several saturated FAs. This indicates that XSP10 binds saturated FAs weakly but significantly. To look at XSP10s role in Fol infection XSP10-silenced plant lines were constructed.

Fol resistance was tested on control and XSP10-silenced plants using a disease index. Both sets of plants were either mock infected or infected with Fol and then scored 0-4 with 0 indicating no infection and 4 indicating dead or very small and wilted plants. The transgenic plants showed fewer disease symptoms, fewer dead plants and greater plant weight as compared with the infected control plants. Most of the conclusions were supported by the data.

However, plant weight in the infected XSP10-silenced plants does not seem to be significantly greater than that of the infected control plants. The error bars on graph 3A of the transgenic infected plants (X1+, X2+ and X3+) seems to overlap the error bars of the control infected plants (C+). However, visually the transgenic infected plants (X1+, X2+ and X3+) pictured in figure 3C do seem larger than the control infected plants (C+), but perhaps not significantly so.

Several more future experiments are needed to determine whether or not XSP10 is an LTP and what its role is in Fol infection. Although XSP10 was shown to weakly bind saturated FAs, measuring intrinsic changes in fluorescence should be done to determine XSP10s specificity for certain substrates as well as dissociation constants. Also, it was shown that XSP10-silenced plants have reduced symptoms of Fol infection. However, there are two possible explanations for this. The first is that reduced.