Abstract
Paulownia witches’ broom (PaWB), caused by phytoplasma, is an important disease of Paulownia. To further identify the key miRNAs associated with the formation of PaWB symptoms, miRNA and degradome sequencing were performed to explore important miRNAs–target regulation in healthy and diseased Paulownia tomentosa, Paulownia fortunei, and P. tomentosa × P. fortunei seedlings, and the corresponding diseased seedlings treated with 75 mg L−1 dimethyl sulfate. A total of 212, 111, and 197 differentially expressed miRNAs (DEMs) were obtained in P. tomentosa, P. fortunei, and P. tomentosa × P. fortunei, respectively. Degradome sequencing detected 559, 251, and 568 target genes of the DEMs in P. tomentosa, P. fortunei, and P. tomentosa × P. fortunei, respectively. The expression patterns of selected miRNAs and the target genes were verified be qRT-PCR. Through analysis of the expression level of the DEMs in this study, combined with the results in our previous studies, as well as with those reported in other phytoplasma-infected plants, we concluded that miR156 is an important miRNA related to witches’ broom. According to the functions of the target genes of DEMs, we constructed a co-regulatory network of the DEMs-target genes interaction. These results will help to advance the understanding of the mechanism of PaWB.
Highlights
Paulownia are fast-growing trees native to China and have been cultivated for their environmental protection and commercial importance, but they are susceptible to Paulownia witches’ broom (PaWB), which is one of the most devastating diseases caused by phytoplasma
We explored key miRNA changes associated with the PaWB symptom forming process by small RNA sequencing, and used degradome sequencing to predict the target of miRNA
The results showed that differentially expressed miRNAs (DEMs) and their target genes’ expression had a negative regulation pattern (Figures 4 and 5), and there was a strong correlation between the read abundances in the sequencing data and the expression levels obtained by qRT-PCR (Figure S2 and Figure 4)
Summary
Paulownia are fast-growing trees native to China and have been cultivated for their environmental protection and commercial importance, but they are susceptible to Paulownia witches’ broom (PaWB), which is one of the most devastating diseases caused by phytoplasma. Paulownia with witches’ brooms include short internodes, yellowing or reddening of leaves, stunting and decline, phyllody and virescence of flowers, sterile flowers and necrosis, and altered volatile production [1,2]. Phytoplasmas are obligate intracellular parasites with no cell walls that belong to the class Mollicutes. They have small genomes (about 530–1350 kb) with 23–29% GC content and can infect more than 1000 different plant species [3]. Accumulating evidence has revealed the gene, protein, and metabolite changes in Forests 2018, 9, 302; doi:10.3390/f9060302 www.mdpi.com/journal/forests
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