Sgt1, but not Rar1, is essential for the RB-mediated broad-spectrum resistance to potato late blight

<p>Abstract</p> <p>Background</p> <p>Late blight is the most serious potato disease world-wide. The most effective and environmentally sound way for controlling late blight is to incorporate natural resistance into potato cultivars. Several late blight resistance genes have been cloned recently. However, there is almost no information available about the resistance pathways mediated by any of those genes.</p> <p>Results</p> <p>We previously cloned a late blight resistance gene, <it>RB</it>, from a diploid wild potato species <it>Solanum bulbocastanum</it>. Transgenic potato lines containing a single <it>RB </it>gene showed a rate-limiting resistance against all known races of <it>Phytophthora infestans</it>, the late blight pathogen. To better understand the <it>RB</it>-mediated resistance we silenced the potato <it>Rar1 </it>and <it>Sgt1 </it>genes that have been implicated in mediating disease resistance responses against various plant pathogens and pests. The <it>Rar1 </it>and <it>Sgt1 </it>genes of a <it>RB</it>-containing potato clone were silenced using a RNA interference (RNAi)-based approach. All of the silenced potato plants displayed phenotypically normal growth. The late blight resistance of the <it>Rar1 </it>and <it>Sgt1 </it>silenced lines were evaluated by a traditional greenhouse inoculation method and quantified using a GFP-tagged <it>P. infestans </it>strain. The resistance of the <it>Rar1</it>-silenced plants was not affected. However, silencing of the <it>Sgt1 </it>gene abolished the <it>RB</it>-mediated resistance.</p> <p>Conclusion</p> <p>Our study shows that silencing of the <it>Sgt1 </it>gene in potato does not result in lethality. However, the <it>Sgt1 </it>gene is essential for the <it>RB</it>-mediated late blight resistance. In contrast, the <it>Rar1 </it>gene is not required for <it>RB</it>-mediated resistance. These results provide additional evidence for the universal role of the <it>Sgt1 </it>gene in various <it>R </it>gene-mediated plant defense responses.</p

, but not , is essential for the -mediated broad-spectrum resistance to potato late blight-3

Control (+); Katahdin: susceptible control (-); PT29: a clone as the resistant control (+); Non-silenced line (+): a transgenic, but non-silenced -RNAi line (clone 3007); RNAi line #1 (silenced, +, clone 3128); RNAi line #2 (silenced, +, clone 2998); RNAi line (silenced, +, clone 3095); Non-silenced line (+): a non-silenced -RNAi line (clone 3061). Error bars represent the standard deviation from the means.<p><b>Copyright information:</b></p><p>Taken from ", but not , is essential for the -mediated broad-spectrum resistance to potato late blight"</p><p>http://www.biomedcentral.com/1471-2229/8/8</p><p>BMC Plant Biology 2008;8():8-8.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2267190.</p><p></p

, but not , is essential for the -mediated broad-spectrum resistance to potato late blight-5

L (+); Non-silenced line (+): a transgenic, but non-silenced -RNAi line (clone 3007); A -RNAi line (clone 3128); Non-silenced line (+): a non-silenced -RNAi line (clone 3061); A -RNAi line (clone 3095). Using a one-way ANOVA, with unequal variance, and Fisher's LSD at an alpha of 0.01, the only group that has significantly higher sporangial growth is the -silenced line.<p><b>Copyright information:</b></p><p>Taken from ", but not , is essential for the -mediated broad-spectrum resistance to potato late blight"</p><p>http://www.biomedcentral.com/1471-2229/8/8</p><p>BMC Plant Biology 2008;8():8-8.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2267190.</p><p></p

, but not , is essential for the -mediated broad-spectrum resistance to potato late blight-4

inoculation and photographed on a dissecting microscope under a narrow-band GFP filter. Untransformed K41 control. Katahdin. A silenced -RNAi line (clone 3128). A -silenced line (clone 3095). The red circles outline the original location of the 10 μl inoculation drops. Green fluorescence is only observed within the circles in A and C but spreads out of the original inoculation sites in B and D. Bars = 2.5 mm.<p><b>Copyright information:</b></p><p>Taken from ", but not , is essential for the -mediated broad-spectrum resistance to potato late blight"</p><p>http://www.biomedcentral.com/1471-2229/8/8</p><p>BMC Plant Biology 2008;8():8-8.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2267190.</p><p></p

Schematic representation of the potato and genes and regions used for RNAi construct development

<p><b>Copyright information:</b></p><p>Taken from ", but not , is essential for the -mediated broad-spectrum resistance to potato late blight"</p><p>http://www.biomedcentral.com/1471-2229/8/8</p><p>BMC Plant Biology 2008;8():8-8.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2267190.</p><p></p

, but not , is essential for the -mediated broad-spectrum resistance to potato late blight-1

) containing the -RNAi construct but not silenced; Lane 2–4: three independent -silenced lines (clones 3128, 2998, 3028) showing no transcript; Lane 5: untransformed K41 control. Northern blot analysis of transcription of the gene. Lane 1: a transgenic plant (clone 3061) containing the -RNAi construct but not silenced; Lane 2: -silenced line (clone 3095) showing no transcript; Lane 3: untransformed K41 control. Both blots were re-probed with an actin gene probe to ensure equal loading of mRNA in each lane.<p><b>Copyright information:</b></p><p>Taken from ", but not , is essential for the -mediated broad-spectrum resistance to potato late blight"</p><p>http://www.biomedcentral.com/1471-2229/8/8</p><p>BMC Plant Biology 2008;8():8-8.</p><p>Published online 23 Jan 2008</p><p>PMCID:PMC2267190.</p><p></p