Abstract
BackgroundCucumber downy mildew, caused by P. cubensis, is an important leaf disease that can severely affect cucumber production. In recent years, cucumber target spot, caused by C. cassiicola, has been reported in both Asia and Europe and is now considered as a major disease disrupting cucumber production. Single-disease-resistant cucumber varieties have been unable to satisfy production needs.To explore the molecular mechanisms of cucumber resistance to these two diseases, cucumber cultivars D9320 (resistant to downy mildew and target spot) and D0401 (susceptible to downy mildew and target spot) were used as experimental materials in this study. We used transcriptome sequencing technology to identify genes related to disease resistance and verified using transgenic technology.ResultsWe screened out the cucumber resistance-related gene CsERF004 using transcriptome sequencing technology. Induction by pathogens, salicylic acid (SA), and ethylene (ET) resulted in the up-regulation of CsERF004. Three treatments, namely, inoculation with C. cassiicola alone, inoculation with P. cubensis alone, and simultaneous inoculation with both pathogens, all resulted in the significant and sustained up-regulation of CsERF004 in the resistant cultivar D9320, during the early stage of infection. In the susceptible cultivar D0401, CsERF004 expression was also significantly up-regulated at the later stage of infection but to a lesser extent and for a shorter duration than in the resistant cultivar D9320. The CsERF004 gene encodes a protein localizes to the nucleus. The over-expression of CsERF004 in the susceptible cultivar D0401 resulted in the significant up-regulation of the CsPR1 and CsPR4 genes and increased the levels of SA and ET, which enhanced the resistance of cucumber to downy mildew and target spot.ConclusionsAnalyses of the CsERF004 expression pattern in disease-resistant and susceptible cucumber cultivars and transgenic validation indicate that CsERF004 confers resistance to P. cubensis and C. cassiicola. The findings of this study can help to better understanding of mechanisms of response to pathogens and in establishment the genetic basis for the development of cucumber broad-spectrum resistant cultivars.
Highlights
Cucumber downy mildew, caused by P. cubensis, is an important leaf disease that can severely affect cucumber production
Two major diseases that affect cucumber production are cucumber downy mildew caused by Pseudoperonospora cubensis (Berk. & M.A.Curtis, Rostovzev) [1] and cucumber target spot caused by Corynespora cassiicola (Berk & Curt, Wei) [2]
Transcriptome sequencing after the three treatments identified 61 up-regulated and 276 down-regulated genes in the resistant cultivar D9320 and 427 up-regulated and 763 down-regulated genes in the susceptible cultivar D0401 (Fig. 1)
Summary
Cucumber downy mildew, caused by P. cubensis, is an important leaf disease that can severely affect cucumber production. Two major diseases that affect cucumber production are cucumber downy mildew caused by Pseudoperonospora cubensis & M.A.Curtis, Rostovzev) [1] and cucumber target spot caused by Corynespora cassiicola (Berk & Curt, Wei) [2] Disease epidemics involving these pathogens generally spread quickly, disrupting cucumber production. Some studies reported that resistance to downy mildew is controlled by multiple genes [5,6,7,8,9], while others believe it to result from a single recessive gene [10,11,12,13]. Resistance to target spot is generally believed to be controlled by a single gene Whether this gene is dominant or recessive has been discussed. The study of broadspectrum disease resistance mechanisms can be important to establish the genetic basis for the development of multi-disease-resistant cucumber varieties
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