The Impact of Jujube Witches' Broom Phytoplasma on the Community Structure of Endophytes in Jujube

Abstract

Evidence from an increasing number of studies indicates that plant endophytic microorganisms play a significant role during biotic and abiotic stress resistance. To date, however, only a handful of studies on endophytes in response to the presence of phytoplasmas have been conducted. The production of jujube (Ziziphus jujuba) is threatened by jujube witches' broom (JWB) disease, which is associated with the presence of the JWB phytoplasma 'Candidatus Phytoplasma ziziphi'. To investigate the impact of jujube witches' broom phytoplasma on the endophyte populations in jujube, high-throughput sequencing was performed in healthy and JWB-infected orchard jujube trees and in vitro jujube shoots. The results showed that the presence of JWB phytoplasma in jujube altered the abundance, diversity, and community structure of endophytic bacteria and fungi. In the branches and the roots, the presence of JWB phytoplasma was associated with an increase in the richness of the endophytic communities and a decrease in their diversity, with the phyla Proteobacteria, Firmicutes, and Bacteroidota and the genus 'Ca. Phytoplasma' becoming the most abundant. The presence of phytoplasmas was also associated with the remodeling of the endophytic microorganisms' interaction network, shifting to a simpler biodiversity state. These results demonstrate the response of the jujube endophytic community to the presence of JWB phytoplasmas and shed light on the possible antagonistic agents that could be further evaluated for JWB disease biocontrol.

Keywords: biological control; high-throughput sequencing; microbial diversity; plant disease.

Figure 1

Analysis of the α-diversity of endophytic bacteria and fungi in jujube. (a,c) Chao1 index and (b,d) Shannon Index. The Chao1 and Shannon indices of each sample repeat are presented in dots of certain colors. Outlier data are presented in circles. * indicates a significant difference at the p < 0.05 level. ** indicates a significant difference at the p < 0.01 level. NS indicates no difference at the p ≤ 0.05 level.

Figure 2

Principal component analysis of the endophytic microbial community in jujube. (a) Endophytic bacteria and (b) endophytic fungi. Each point in the figure represents a sample; different colors and shapes represent different samples/groupings; the oval circles indicate that they are 95% confidence ellipses; and the confidence ellipses show when the number of samples is higher than three. The abscissa represents the first principal component, and the percentage indicates the contribution value of the first principal component to the sample differences. The ordinate represents the second principal component, and the percentage indicates the contribution value of the second principal component to the sample differences.

Figure 3

The Venn diagram merges with the columnar statistical chart, showing the unique, shared and total (a) bacterial ASVs and (b) fungal ASVs among the different samples.

Figure 4

The impact of jujube witches’ broom on the composition of the endophytic microbial community at (a) the phylum level of endophytic bacteria; (b) the genus level of endophytic bacteria; (c) the phylum level of endophytic fungi; and (d) the genus level of endophytic fungi.

Figure 5

Analysis of the differences in endophytic microbial genera levels between the groups: (a) endophytic bacteria and (b) endophytic fungi. Different colors in the figure represent different groups or samples. In each picture, the graph on the left-hand side illustrates the abundance proportions of different species in two samples or two groups of samples. The middle section illustrates the different proportions of species abundances within the 95% confidence interval. The value on the far right is the p-value.

Figure 6

The impact of jujube witches’ broom on the functions of the endophytic microbial community in jujube: (a) endophytic bacteria and (b) endophytic fungi.

Figure 7

Correlation network analysis of endophytic bacterial–fungal communities in jujube at the genus level. (a) Analysis of the interactions between endophytic bacteria and fungi in the healthy group and (b) analysis of the interactions between endophytic bacteria and fungi in the diseased group.