Abstract
The American pokeweed plant, Phytolacca americana, displays broad-spectrum resistance to plant viruses and is a heavy metal hyperaccumulator. However, little is known about the regulation of biotic and abiotic stress responses in this non-model plant. To investigate the control of miRNAs in gene expression, we sequenced the small RNA transcriptome of pokeweed treated with jasmonic acid (JA), a hormone that mediates pathogen defense and stress tolerance. We predicted 145 miRNAs responsive to JA, most of which were unique to pokeweed. These miRNAs were low in abundance and condition-specific, with discrete expression change. Integration of paired mRNA-Seq expression data enabled us to identify correlated, novel JA-responsive targets that mediate hormone biosynthesis, signal transduction, and pathogen defense. The expression of approximately half the pairs was positively correlated, an uncommon finding that we functionally validated by mRNA cleavage. Importantly, we report that a pokeweed-specific miRNA targets the transcript of OPR3, novel evidence that a miRNA regulates a JA biosynthesis enzyme. This first large-scale small RNA study of a Phytolaccaceae family member shows that miRNA-mediated control is a significant component of the JA response, associated with widespread changes in expression of genes required for stress adaptation.
Highlights
The American pokeweed, Phytolacca americana, is a non-model plant with promising applications in agriculture
Our results indicate that many defenserelated genes are regulated by jasmonic acid (JA)-induced miRNAs, including the JA biosynthesis gene OPDA reductase 3 (OPR3)
Through time-course analysis, we established previously that pokeweed antiviral protein (PAP) is expressed maximally 24 h following JA treatment (Klenov et al, 2016). This time point was chosen for both the mRNA transcriptome-wide analysis of pokeweed (Neller et al, 2016) and the current paired miRNA analysis, as we were interested in identifying defense genes co-expressed with PAP
Summary
The American pokeweed, Phytolacca americana, is a non-model plant with promising applications in agriculture. Pokeweed synthesizes pokeweed antiviral protein (PAP), a ribosome inactivating protein with RNA N-glycosidase activity (Endo et al, 1988). Several mutants of PAP have been generated and expressed heterologously in transgenic plants to impart novel antiviral and antifungal properties (Zoubenko et al, 1997, 2000; Wang et al, 1998; Dai et al, 2003). Pokeweed is a heavy metal hyperaccumulator with a potential role in phytoremediation (Peng et al, 2008; Liu et al, 2010; Zhao et al, 2011)
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