Phytoplasma-Responsive microRNAs Modulate Hormonal, Nutritional, and Stress Signalling Pathways in Mexican Lime Trees

Abstract

BackgroundWitches’ broom disease of Mexican lime (Citrus aurantifolia L.), which is associated to the phytoplasma ‘Candidatus Phytoplasma aurantifolia’, is a devastating disease that results in significant economic losses. Plants adapt to biotic stresses by regulating gene expression at the transcriptional and post-transcriptional levels. MicroRNAs (miRNAs) are a recently identified family of molecules that regulate plant responses to environmental stresses through post-transcriptional gene silencing.MethodsUsing a high-throughput approach to sequence small RNAs, we compared the expression profiles of miRNAs in healthy Mexican lime trees and in plants infected with ‘Ca. P. aurantifolia’.ResultsOur results demonstrated the involvement of different miRNAs in the response of Mexican lime trees to infection by ‘Ca. P. aurantifolia’. We identified miRNA families that are expressed differentially upon infection with phytoplasmas. Most of the miRNAs had variants with small sequence variations (isomiRs), which are expressed differentially in response to pathogen infection.ConclusionsIt is likely that the miRNAs that are expressed differentially in healthy and phytoplasma-infected Mexican lime trees are involved in coordinating the regulation of hormonal, nutritional, and stress signalling pathways, and the complex interactions between them. Future research to elucidate the roles of these miRNAs should improve our understanding of the level of diversity of specific plant responses to phytoplasmas.

Comparative Analysis of MicroRNA Expression in Three Paulownia Species with Phytoplasma Infection

“…Thence, we compared the common DEMs in the three paulownia species with the DEMs detected in our previous studies [23,[51][52][53][54], and found that miR156, miR398, miR408, and miR2118 were common DEMs in the healthy vs. phytoplasma-infected seedling comparisons. Thirdly, to confirm the key miRNAs related to witches' broom, we compared the four identified miRNAs with the miRNAs detected in phytoplasma-infected Mexican lime, Ziziphus jujuba, and mulberry [7, [14][15][16], and found that miR156 was the only common miRNA among the phytoplasma-responsive miRNAs in all these studies. We then analyzed the expression of miR156 in the three paulownia species and compared the expression level of miR156 of other phytoplasma-infected plants, and found their expression levels in most of the above plants were up-regulated in the phytoplasma-infected plants.…”

“…The discovery of miRNAs as gene regulators has broadened the perspectives of the mechanisms involved in gene regulation, and revealed that miRNAs are associated with many biological processes such as plant development, protein degradation, cell proliferation and differentiation, and signal transduction, and play important roles in resistance to abiotic and biotic stresses [12,13]. A number of studies of plant-phytoplasma interactions have shown that miRNAs are involved in gene regulation in many plants, including Mexican lime, Mulberry, Catharanthus roseus, Peanuts, and Ziziphus jujube [14][15][16]. Some miRNA families are conserved among various plants; however, changes in their expression patterns in response to different phytoplasma infections were different in different plants.…”

“…Some miRNA families are conserved among various plants; however, changes in their expression patterns in response to different phytoplasma infections were different in different plants. In Mexican lime infected with Candidatus Phytoplasma aurantifolia, a high expression of miR157 was shown to regulate changes in the leaf morphology of infected seedlings [15] In mulberry trees infected with Aster yellows phytoplasma, a high expression of miR393a was associated with changes in the morphology of infected mulberry seedlings, and upregulation of miR482a-5p was shown to be responsible for some symptoms in the infected plants [7,16]. In Ziziphus jujube infected with Candidatus Phytoplasma ziziphi, overexpression of miR156b increased axillary branching, aberrantly expressed miR159 mediated MYB33, and the miR156-SPL-miR172 regulatory pathway was thought to lead to trolled leaf and shorter petioles and the development of green leaf-like structures instead of flowers, as well as the sterility of flowers [14].…”

Genome-Wide Identification and Analysis of MicroRNAs Involved in Witches’-Broom Phytoplasma Response in Ziziphus jujuba

“…The 5’-RLM-RACE experiments were carried out using the modified RNA ligase-mediated rapid amplification of 5’ cDNAs method as described [28,29], PCRs were carried out on mRNA isolated from Z . jujuba infected with witches’-broom disease using the GeneRacer 5’ primer and the nesting gene-specific primers (S2 Table).…”

Metabolite profiling of Mexican lime (Citrus aurantifolia) leaves during the progression of witches’ broom disease

“…P. aurantifolia" Zamharir et al, 2011). Ehya et al (2013) detected miRNA families that are expressed differently upon infection with phytoplasma species. Most of the miRNAs had variants with small sequence variations (isomiRs), which are expressed differently in response to pathogen infection.…”