Analysis of leaf morphology, secondary metabolites and proteins related to the resistance to Tetranychus cinnabarinus in cassava (Manihot esculenta Crantz)

Abstract

Constitutive resistance of plant can be divided into physical and chemical barriers. Cassava (Manihot esculenta Crantz) is susceptible to mites, especially Tetranychus cinnabarinus. Although significant differences in the resistance to T. cinnabarinus are observed in different cassava cultivars, limited research has been done on the mechanism accounting for the resistance. The aim of this study was to explore the mechanism of resistance to T. cinnabarinus by comparing morphology, secondary metabolites and proteins in different cassava cultivars. The anatomical structure of leaves showed that the cassava cultivar Xinxuan 048 (XX048), which showed a stronger resistance to T. cinnabarinus in both greenhouse testing and three years field evaluation tests (2016-2018), had thicker palisade tissue, spongy tissue, lower epidermis and leaf midrib tissue compared to cultivar Guire 4 (GR4). Greenhouse evaluation demonstrated that originally these cultivars were different, leading to differences in constitutive levels of metabolites. The proteomic analysis of protected leaves in XX048 and GR4 revealed that up-regulated differentially expressed proteins (DEPs) were highly enriched in secondary metabolic pathways, especially in the biosynthesis of flavonoids. This study not only provides a comprehensive data set for overall proteomic changes of leaves in resistant and susceptible cassava, but also sheds light on the morphological characteristics of cassava-mite interaction, secondary metabolite defense responses, and molecular breeding of mite-resistant cassava for effective pest control.

Figure 1

Comparison of leaf morphological and anatomical characteristics of the leaves from different cassava cultivars. (A,B) pictures of both sides of the cassava leaf from XX048 (A) and GR4 (B); (C,D) transverse sections of XX048 (C) and GR4 (D) leaves; E and F, leaf midrib of XX048 (E) and GR4 (F) leaves. (C,D: 10 × 40; E,F: 10 × 20). I: Upper epidermis II: Palisade tissue III: Spongy tissue IV: Lower epidermis V: Leaf midrib. These values are presented as the mean ± standard deviation (SD) based on three biologically independent values. Letters above the histogram indicate the statistical significance (p < 0.05).

Figure 2

Comparison of secondary metabolites content in leaves of XX048 and GR4 affected by T. cinnabarinus from 2016 to 2018 in the field.

Figure 3

Comparison of secondary metabolites content in leaves protected or affected by T. cinnabarinus in greenhouse. These values are presented as the mean ± standard deviation (SD) based on three biologically independent values. Letters above the histogram indicate the statistical significance (p < 0.05).

Figure 4

General information of the identified proteins. (A) The protein information; (B) The distribution of protein molecular weight; (C) The peptide length distribution coverage; (D) Venn diagram showing quantitative distribution of differentially expressed proteins in the samples of XX048 and GR4, respectively.

Figure 5

Protein domain analysis of the DEPs.

Figure 6

KEGG enrichment analysis of the DEPs in XX048 and GR4 cassava leaves.

Figure 7

PPI network analysis of DEPs in XX048 and GR4 cassava leaves. DEPs related to amino acid metabolism, biosynthesis of other secondary metabolites, carbohydrate metabolism, metabolism of terpenoids and polyketides and lipid metabolism were indicated in backgrounds of blue, red, yellow pink and purple, respectively. Each node in the figure represents a protein, and the size of nodes indicates the degree of correlation between proteins. Each line indicates the interaction between proteins. The green and red dots represent down-regulation and up-regulation, respectively.

Figure 8

Relative expressions of 11 genes at the protein and mRNA levels.