Transcriptional Reprogramming Induced by BTH in Tomato, Molecular Changes in Response to the Stress Caused by Bemisia tabaci Infestation and Comparison with Mi-1-Mediated Resistance

Benzo-(1,2,3)-thiadiazole-7-carbothioic acid S-methyl ester (BTH), a salicylic acid (SA) analogue, induces resistance to several tomato pests and pathogens, including the whitefly Bemisia tabaci. However, the transcriptional mechanisms underlying BTH-induced responses to the biotic stress due to infestation by this insect remain incompletely understood. Here, we first investigated whether BTH treatment alters the tomato transcriptome consistently with activation of SA-associated defence. Gene expression in BTH-treated and untreated plants of susceptible tomato cv. Moneymaker was analysed using the Affymetrix GeneChip Tomato Genome Array. BTH treatment resulted in 1280 differentially expressed transcripts, including 502 upregulated and 778 downregulated transcripts. This was associated with increased expression of defence-related genes, including WRKY transcription factors and pathogenesis-related proteins, together with repression of genes involved in jasmonic acid signalling and photosynthetic processes. Subsequent B. tabaci infestation only slightly modified these transcriptional changes, with most differential transcripts shared between infested and uninfested plants. Comparison of BTH-treated Moneymaker with resistant Motelle (carrying the Mi-1 gene) identified 1241 differentially expressed transcripts. Overall, the results support a model in which BTH establishes a distinct SA-associated transcriptional state that is relatively stable following B. tabaci attack, while differing substantially from the constitutive transcriptomic profile associated with Mi-1-mediated genetic resistance.