Xiaofeng Zhu

Proteomic analysis of the bacterial induction of resistance to atrazine in soybean leaves

Atrazine is a photosystem-II-inhibiting herbicide that interferes with photosynthetic electron transport, resulting in oxidative stress. Soybean (Glycine max (L.) Merrill) is an atrazine-sensitive crop, and its productivity is severely impacted by soils containing atrazine residues. Our previous study indicated that the bacteria Klebsiella pneumoniae strain SnebYK-induced resistance to atrazine in soybean, both before and after pasteurization. In order to study the molecular mechanisms of this induced resistance, proteins change in soybean leaves induced by SnebYK was investigated using two-dimensional gel electrophoresis. Differentially expressed proteins (relative to a non-induced control) were identified using MALDI-TOF MS. Differential expression patterns were detected in soybean leaves that had been induced by the bacterium. Analysis of relative expression levels indicated up-regulation of most of the mRNAs in these samples relative to the control. The corresponding proteins were observed to be involved primarily in physiological processes, including active oxygen removal, resistance signal transduction, and photosynthesis. This is the first study to conduct proteomic analysis of a soybean resistance response induced by bacteria. It is plausible that these differentially expressed proteins may interact to play a major role in defense and/or resistance responses.

The Role of Sugar Transporter Genes during Early Infection by Root-Knot Nematodes

Although pathogens such as nematodes are known to hijack nutrients from host plants, the mechanisms whereby nematodes obtain sugars from plants remain largely unknown. To determine the effects of nematode infection on host plant sugar allocation, soluble sugar (fructose, glucose, sucrose) content was investigated using high-performance liquid chromatography with refractive index detection and was found to increase significantly in tomato (Solanum lycopersicum, Sl) leaves and roots during early infection by root-knot nematodes (RKNs). To further analyze whether sugar transporters played a role in this process, the expression levels of sucrose transporter (SUT/SUC), Sugars Will Eventually be Exported Transporter (SWEET), tonoplast monosaccharide transporter (TMT), and vacuolar glucose transporter (VGT) gene family members were examined by qRT-PCR analysis after RKN infection. The results showed that three SlSUTs, 17 SlSWEETs, three SlTMTs, and SlVGT1 were upregulated in the leaves, whereas three SlSUTs, 17 SlSWEETs, two SlTMTs, and SlVGT1 were induced in the roots. To determine the function of the sugar transporters in the RKN infection process, we examined post-infection responses in the Atsuc2 mutant and pAtSUC2-GUS lines. β-glucuronidase expression was strongly induced at the infection sites, and RKN development was significantly arrested in the Atsuc2 mutant. Taken together, our analyses provide useful information for understanding the sugar transporter responses during early infection by RKNs in tomato.

Effect of Sinorhizobium fredii strain Sneb183 on the biological control of soybean cyst nematode in soybean

The soybean cyst nematode (SCN; Heterodera glycines) is a major detriment to soybean production. The endophytic bacterium Sinorhizobium fredii strain Sneb183 is known to inhibit the activity of SCN. In the present study, soybean seedlings were inoculated with Sneb183, to study the penetration juveniles, and their development inside the roots. The number of cysts in the soybean roots was also examined. The induced systemic resistance in soybean was also examined through the split‐root system. Our results revealed that the number of juveniles and cysts significantly decreased as a result of Sneb183 inoculation. Sneb183 also prolonged the developmental stage of SCN in the root to 30 days as compared to 27 days in the control. Furthermore, the number of nematodes in each stage was lower in the Sneb183 treated plants than control plants. We also used a split‐root system to show that the S. fredii strain Sneb183 induced a systemic resistance to SCN infection in soybean. The repression rate of SCN penetration was 38.75%. Our study showed that Sneb183 can be an effective biocontrol agent for managing SCN infestation in soybean.

Cactodera chenopodiae (Nematoda: Heteroderidae), a new species of cyst nematode parasitizing common lambsquarter (Chenopodium album) in Liaoning, China.

A new species of cyst nematode, Cactodera chenopodiae n. sp., parasitizing common lambsquarter, Chenopodium album L., is described from native vegetation in Liaoning, China. Cactodera chenopodiae n. sp. has a circumfenestrate pattern typical of the genus and is morphologically similar to C. cacti Krall Krall, 1978. However, in the new species, females and cysts show a larger L/W ratio whereas second-stage juveniles (J2s) have a longer hyaline region. The new species is also morphologically similar to C. milleri Graney Bird, 1990, but the J2s differ by a larger b ratio and longer tail. Based on DNA sequences of the 28S and ITS rRNA, C. chenopodiae n. sp. comes close to C. estonica Krall Krall, 1978, although it is distinct from the latter with respect to the presence of a punctate eggshell and larger b ratio in the J2s. Although morphometric comparisons with additional Cactodera species show the overlapping of diagnostic morphological characters, our phylogenetic analyses based on both rRNA genes support C. chenopodiae n. sp. as a unique lineage.

The cold tolerance of the northern root-knot nematode, Meloidogyne hapla

The northern root-knot nematode, Meloidogyne hapla, is one of the most important nematode pathogens occurring in cold regions. It is a sedentary, biotrophic parasites of plants and overwinter in the soil or in diseased roots. This study showed that the cold tolerance for the second-stage juveniles (J2) of M. hapla was moderate with the 50% survival temperature (S50) of -2.22°C and the fatal temperature was -6°C when cooling at 0.5°C min-1. Cryoprotective dehydration significantly enhance cold tolerance of M. hapla J2 with the lowest S50 of -3.28°C after held being at -1°C for 6 h. Moreover, cold shock and cold acclimation had significant effects on the freezing survival of M. hapla J2. The lethal temperature of eggs was -18°C. Therefore, the cold tolerance of M. hapla is sufficiently favorable to withstand winters in cold temperature environments.

The transcriptomic changes of Huipizhi Heidou (Glycine max), a nematode-resistant black soybean during Heterodera glycines race 3 infection

Glycine max (soybean) is an extremely important crop, representing a major source of oil and protein for human beings. Heterodera glycines (soybean cyst nematode, SCN) infection severely reduces soybean production; therefore, protecting soybean from SCN has become an issue for breeders. Black soybean has exhibited a different grade of resistance to SCN. However, the underlying mechanism of Huipizhi Heidou resistance against SCN remains elusive. The Huipizhi Heidou (ZDD2315) and race 3 of Heterodera glycines were chosen to study the mechanism of resistance via examination of transcriptomic changes. After 5, 10, and 15days of SCN infection, whole roots were sampled for RNA extraction, and uninfected samples were simultaneously collected as a control. 740, 1413, and 4925 genes were isolated by padj (p-value adjusted)<0.05 after 5, 10, and 15days of the infection, respectively, and 225 differentially expressed genes were overlapped at all the time points. We found that the differentially expressed genes (DEGs) at 5, 10, and 15days after infection were involved in various biological function categories; in particular, induced genes were enriched in defense response, hormone mediated signaling process, and response to stress. To verify the pathways observed in the GO and KEGG enrichment results, effects of hormonal signaling in cyst-nematode infection were further examined via treatment with IAA (indo-3-acetic acid), salicylic acid (SA), gibberellic acid (GA), jasmonic acid (JA), and ethephon, a precursor of ethylene. The results indicate that five hormones led to a significant reduction of J2 number in the roots of Huipizhi Heidou and Liaodou15, representing SCN-resistant and susceptible lines, respectively. Taken together, our analyses are aimed at understanding the resistance mechanism of Huipizhi Heidou against the SCN race 3 via the dissection of transcriptomic changes upon J2 infection. The data presented here will help further research on the basis of soybean and cyst-nematode interaction.

Klebsiella pneumoniae SnebYK Mediates Resistance Against Heterodera glycines and Promotes Soybean Growth

Soybean is an important economic crop that is often adversely affected by infection in the field with the soybean cyst nematode Heterodera glycines. Biological control is an eco-friendly method used to protect the crop against disease. The bacterium Klebsiella pneumoniae has been reported to protect rice from sheath blight and seedling blight, but its role in the control of nematode is unclear. In this study, the effect of K. pneumoniae SnebYK on the control of H. glycines was assessed. Potting experiment results showed that coating soybean seeds with K. pneumoniae SnebYK not only reduced the infection rate of H. glycines but also decreased the proportion of adult female nematodes. Field experiment results showed that K. pneumoniae SnebYK reduced both the number of H. glycines in soybean roots and the number of adult females. However, K. pneumoniae SnebYK caused low juvenile mortality in an in vitro assay. To further analyze the role of K. pneumoniae SnebYK in the inhibition of H. glycines infection, split root experiments were conducted. The results indicated that K. pneumoniae SnebYK controls H. glycines via induced systemic resistance, which reduces H. glycines penetration. Klebsiella pneumoniae SnebYK treatment also significantly increased the proportion of second-stage juveniles and decreased the proportions of third- and fourth-stage juveniles in the H. glycines population. Moreover, 48 h after inoculation with H. glycines, the expression levels of PR1, PR2, PR5, and PDF1.2 were significantly higher in soybeans pretreated with K. pneumoniae SnebYK than in control soybeans. Interestingly, besides providing protection against nematodes, K. pneumoniae SnebYK fixed nitrogen, produced ammonia, solubilized phosphate, and produced siderophores, leading to well-developed root system and an increase in soybean seedling fresh weight. These results demonstrate for the first time that K. pneumoniae SnebYK not only promotes soybean growth but also inhibits the invasion and development of H. glycines by inducing systemic resistance.

Transcriptomic and metabolomic analyses reveal that bacteria promote plant defense during infection of soybean cyst nematode in soybean

BackgroundSoybean cyst nematode (SCN) is the most devastating pathogen of soybean. Our previous study showed that the plant growth-promoting rhizobacterium Bacillus simplex strain Sneb545 promotes soybean resistance to SCN. Here, we conducted a combined metabolomic and transcriptomic analysis to gain information regarding the biological mechanism of defence enhancement against SCN in Sneb545-treated soybean. To this end, we compared the transcriptome and metabolome of Sneb545-treated and non-treated soybeans under SCN infection.ResultsTranscriptomic analysis showed that 6792 gene transcripts were common in Sneb545-treated and non-treated soybeans. However, Sneb545-treated soybeans showed a higher concentration of various nematicidal metabolites, including 4-vinylphenol, methionine, piperine, and palmitic acid, than non-treated soybeans under SCN infection.ConclusionsOverall, our results validated and expanded the existing models regarding the co-regulation of gene expression and metabolites in plants, indicating the advantage of integrated system-oriented analysis.