Abstract
The salicylic acid (SA) plays a critical role during the establishment of systemic acquired resistance (SAR) in uninfected plant tissues after localised exposure to a pathogen. Here, we studied SA in Populus tomentosa infected by the plant pathogen Botryosphaeria dothidea. The accumulation of SA and methyl salicylate (MeSA) occurred in chronological order in P. tomentosa. The SA and MeSA contents were greater at infected than uninfected sites. Additionally, a gene expression analysis indicated that SA might be accumulated by phenylalanine ammonialyase (PAL) and converted to MeSA by SA carboxyl methyltransferase (SAMT), while MeSA might convert to SA by SA-binding protein 2 (SABP2). The expressions of SAMT at infected sites and SABP2 at uninfected sites, respectively, were significantly up-regulated. Thus, SA might be converted to MeSA at infected sites and transported as a signalling molecule to uninfected sites, where it is converted to SA for SAR. Moreover, the expressions of pathogenesis-related genes PR-1, PR-2 and PR-5 in P. tomentosa were up-regulated by the B. dothidea infection. Our study determined that variations in SA and MeSA contents occur at infected and uninfected sites in poplar after pathogen infection and contributed to the remote signals for poplar SAR.
Highlights
During evolution, plants evolved complex mechanisms to adapt to pathogen attack, wounds, heat and other environmental stresses[1,2,3,4]
To further define the role of salicylic acid (SA) and its correlation to the methyl salicylate (MeSA) content, we determined the MeSA content, which was significantly increased in P. tomentosa after inoculation with B. dothidea
Large amounts of SA accumulated in P. tomentosa tissues after inoculation with B. dothidea, while the control did not induce SA accumulation under the same conditions, indicating that the changes in SA were closely correlated with the B. dothidea
Summary
Plants evolved complex mechanisms to adapt to pathogen attack, wounds, heat and other environmental stresses[1,2,3,4]. The reduction of MeSA in primary infected leaves by either the overexpression of a mutant SABP2 or the silencing of SAMT results in the loss of SAR and the suppression of PR gene expression levels[20,21]. Botryosphaeria dothidea (Mougeot ex Fries) Cesati et de Notaris is a plant pathogen that causes the formation of cankers on a wide variety of tree and shrub species. This species infects several hundred plant hosts on all continents, except Antarctica[29,30]. SA treatments can induce the expression of defence genes in poplar[32], suggesting that the SA signalling pathway may be very important for SAR in poplar. Our aim was to clarify the role of SA and its signal transduction mechanism during P. tomentosa–B. dothidea interactions
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