Silicon modulates expression of pathogen defense-related genes during alleviation of copper toxicity in Nicotiana tabacum

Plants treated with metals better fend off infection by pathogens. This activity is mediated, at least in part, by the activation of the salicylic acid (SA) signaling pathway. Previous work in our laboratory demonstrated that silicon (Si) could alleviate copper (Cu) toxicity stress in Nicotiana tabacum. However, how Si affected expression of genes involved in SA biosynthesis and signaling in N. tabacum under Cu stress was unclear. Therefore, we investigated this at two time points. Roots of plants treated with Cu toxicity for one week exhibited increased transcript levels for Isochorismate Synthase1, a gene encoding a key enzyme involved in SA biosynthesis and the addition of Si further enhanced expression. Microarray analysis identified a number of disease defense-associated genes up-regulated in N. tabacum roots after one week of Cu toxicity treatment and further increased when plants were also supplemented with Si. However, the effect of Si on expression of these genes was lost after three weeks of treatment, indicating these effects are dynamic.