Integrated Phloem Sap mRNA and Protein Expression Analysis Reveals Phytoplasma-infection Responses in Mulberry

Abstract

To gain insight into the response of mulberry to phytoplasma-infection, the expression profiles of mRNAs and proteins in mulberry phloem sap were examined. A total of 955 unigenes and 136 proteins were found to be differentially expressed between the healthy and infected phloem sap. These differentially expressed mRNAs and proteins are involved in signaling, hormone metabolism, stress responses, etc. Interestingly, we found that both the mRNA and protein levels of the major latex protein-like 329 () gene were increased in the infected phloem saps. Expression of the gene was induced by pathogen inoculation and was responsive to jasmonic acid. Ectopic expression of in Arabidopsis enhances transgenic plant resistance to , pv tomato DC3000 ( DC3000) and phytoplasma. Further analysis revealed that can enhance the expression of some defense genes and might be involved in altering flavonoid content resulting in increased resistance of plants to pathogen infection. Finally, the roles of the differentially expressed mRNAs and proteins and the potential molecular mechanisms of their changes were discussed. It was likely that the phytoplasma-responsive mRNAs and proteins in the phloem saps were involved in multiple pathways of mulberry responses to phytoplasma-infection, and their changes may be partially responsible for some symptoms in the phytoplasma infected plants.

Expression and functional analysis of a PR-1 Gene, MuPR1, involved in disease resistance response in mulberry (Morus multicaulis)

“…Our data also showed that MuPR1-GFP fusion was localized exclusively to the extracellular spaces (Figure 4(c)). This is consistent in that some PR1s were detected in the phloem saps of several plants, including mulberry, cucurbits, rice, and Arabidopsis (Walz et al 2004;Deeken et al 2008;Gutierrez-Carbonell et al 2015;Gai et al 2018), and some PR1s exhibit vascularspecific expression patterns (Carr et al 1987;Tornero et al 1997). Therefore, MuPR1 proteins could be secreted into the phloem and may play an important role in SAR.…”

Plant Hormones in Phytoplasma Infected Plants

“…P. aurantifolia’ (Monavarfeshani et al, 2013). Increased expression of the gene that encodes the PR-1 protein was shown for mulberry phloem sap infected with phytoplasmas (Gai et al, 2018a).…”

“…Ectopic expression of this gene enhances mulberry resistance to several pathogens, including phytoplasmas. Although treatment of wild-type mulberry seedlings with SA did not affect MuMLPL329 expression, the PR-2 and PR-5 genes were highly expressed in MuMLPL329 -overexpressing transgenic Arabidopsis plants (Gai et al, 2018a).…”

“…Transcriptomic analysis of mulberry phloem sap infected with phytoplasmas showed differential expression of several mRNAs associated with JA metabolism and signaling (Gai et al, 2018a). In leaves of Chinese jujube in an earlier stage after infection of phytoplasma causing jujube witches' broom, there were large changes in a JA-induced protein-like gene transcript.…”

“…Of note, the studies that suggest the plant hormone contribution to pathogenesis are very diverse. The analyses were performed on different parts of plants, e.g., whole leaves (Gai et al, 2014a; Youssef et al, 2018), leaf midribs (Hren et al, 2009; Prezelj et al, 2016a), phloem sap (Gai et al, 2018a); they use different approaches, e.g., direct hormone evaluation (Lazar, 2010) or gene expression analyses (Hren et al, 2009; Musetti et al, 2013; Paolacci et al, 2017); and very different techniques, e.g., HPLC analysis (Youssef et al, 2018), microarray data or real-time PCR analyses (Hren et al, 2009), or RNA-seq data analysis (Snyman et al, 2017). Taking this into account, the results of these studies are not directly comparable.…”