Jasmonate regulates plant resistance to Pectobacterium brasiliense by inducing indole glucosinolate biosynthesis

Comparative transcriptome analysis reveals defense responses against soft rot induced by Pectobacterium aroidearum and Pectobacterium carotovorum in Pinellia ternata

Pectobacterium carotovorum and Pectobacterium aroidearum represent the primary pathogens causing variable soft rot disease. However, the fundamental defense responses of Pinellia ternata to pathogens remain unclear. Our investigation demonstrated that the disease produced by P. carotovorum is more serious than P. aroidearum. RNA-seq analysis indicated that many cell wall-related genes, receptor-like kinase genes, and resistance-related genes were induced by P. aroidearum and P. carotovorum similarly. But many different regulatory pathways exert a crucial function in plant immunity against P. aroidearum and P. carotovorum, including hormone signaling, whereas more auxin-responsive genes were responsive to P. carotovorum, while more ethylene and gibberellin-responsive genes were responsive to P. aroidearum. 12 GDSL esterase/lipase genes and 3 fasciclin-like arabinogalactan protein genes were specifically upregulated by P. carotovorum, whereas 11 receptor-like kinase genes and 8 disease resistance genes were up-regulated only by P. aroidearum. Among them, a lectin gene (part1transcript/39001) was induced by P. carotovorum and P. aroidearum simultaneously. Transient expression in N. benthamiana demonstrated that the lectin gene improves plant resistance to P. carotovorum. This study offers a comprehensive perspective on P. ternata immunity produced by different soft rot pathogens and reveals the importance of lectin in anti-soft rot of P. ternata for the first time.

The endophytic fungal community plays a crucial role in the resistance of host plants to necrotic bacterial pathogens

Konjac species (Amorphophallus spp.) are the only plant species in the world that are rich in a large amount of konjac glucomannan (KGM). These plants are widely cultivated as cash crops in tropical and subtropical countries in Asia, including China. Pectobacterium carotovorum subsp. carotovorum (Pcc) is one of the most destructive bacterial pathogens of konjac. Here, we analyzed the interactions between Pcc and susceptible and resistant konjac species from multiple perspectives. At the transcriptional and metabolic levels, the susceptible species A. konjac and resistant species A. muelleri exhibit similar molecular responses, activating plant hormone signaling pathways and metabolizing defense compounds such as phenylpropanoids and flavonoids to resist infection. Interestingly, we found that Pcc stress can lead to rapid recombination of endophytic microbial communities within a very short period (96 h). Under conditions of bacterial pathogen infection, the relative abundance of most bacterial communities in konjac tissue decreased sharply compared with that in healthy plants, while the relative abundance of some beneficial fungal communities increased significantly. The relative abundance of Cladosporium increased significantly in both kinds of infected konjac compared to that in healthy plants, and the relative abundance in resistant A. muelleri plants was greater than that in susceptible A. konjac plants. Among the isolated cultivable microorganisms, all three strains of Cladosporium strongly inhibited Pcc growth. Our results further elucidate the potential mechanism underlying konjac resistance to Pcc infection, highlighting the important role of endophytic microbial communities in resisting bacterial pathogen infections, especially the more direct role of fungal communities in inhibiting pathogen growth.

Interplay between secondary metabolites and plant hormones in silver nitrate-elicited Arabidopsis thaliana plants

Plants produce a myriad of specialized compounds in response to threats such as pathogens or pests and different abiotic factors. The stress-related induction of specialized metabolites can be mimicked using silver nitrate (AgNO3) as an elicitor, which application in conservation agriculture has gained interest. In Arabidopsis thaliana, AgNO3 triggers the accumulation of indole glucosinolates (IGs) and the phytoalexin camalexin as well as pheylpropanoid-derived defensive metabolites such as coumaroylagmatins and scopoletin through a yet unknown mechanism. In this work, the role of jasmonic (JA) and salicylic acid (SA) signaling in the AgNO3-triggered specialized metabolite production was investigated. To attain this objective, AgNO3, MeJA and SA were applied to A. thaliana lines impaired in JA or SA signaling, or affected in the endogenous levels of IGs and AGs. Metabolomics data indicated that AgNO3 elicitation required an intact JA and SA signaling to elicit the metabolic response, although mutants impaired in hormone signaling retained certain capacity to induce specialized metabolites. In turn, plants overproducing or abolishing IGs production had also an altered hormonal signaling response, both in the accumulation of signaling molecules and the molecular response mechanisms (ORA59, PDF1.2, VSP2 and PR1 gene expression), which pointed out to a crosstalk between defense hormones and specialized metabolites. The present work provides evidence of a crosstalk mechanism between JA and SA underlying AgNO3 defense metabolite elicitation in A. thaliana. In this mechanism, IGs would act as retrograde feedback signals dampening the hormonal response; hence, expanding the signaling molecule concept.

Glucosinolate O-methyltransferase mediated callus formation and affected ROS homeostasis in Arabidopsis thaliana

Auxin-induced callus formation was largely dependent on the function of Lateral Organ Boundaries Domain (LBD) family transcription factors. We previously revealed that two IGMT (Indole glucosinolate oxy-methyl transferase) genes, IGMT2 and IGMT3, may be involved in the callus formation process as potential target genes of LBD29. Overexpression of the IGMT genes induces spontaneous callus formation. However, the details of the IGMT involvement in callus formation process were not well studied. IGMT1-4, but not IGMT5, are targeted and induced by LBD29 during the early stage of callus formation. Cell membrane and nucleus localized IGMT3 was mainly expressed in the elongation and maturation zones tissues of the primary root and lateral root, which could be further accumulated after CIM treatment. The igmts quadruple mutant, which obtained by CRISPR/Cas9 technology, exhibits a phenotype of attenuated callus formation. Enhanced indole glucosinolate anabolic pathway caused by IGMT1-4 overexpression promotes callus formation. In addition, the IGMT genes were involved in the reactive oxygen species homeostasis, which could be responsible for its role on callus formation. This study provides novel insights into the role of IGMTs gene-mediated callus formation. Activation of the Indole glucosinolate anabolic pathway is an inducing factor for plant callus initiation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01409-2.

Rapid Detection and Quantification of Viable Cells of Pectobacterium brasiliense Using Propidium Monoazide Combined with Real-Time PCR

Pectobacterium brasiliense (Pbr) has caused significant economic losses in major vegetable production areas in Northern China by causing bacterial soft rot in cash crops such as potatoes and cucumbers. This study aimed to establish a PMA-qPCR detection method for Pbr by screening specific and sensitive primers based on the glu gene and the conserved region of the 23S rRNA gene. Based on the optimized PMA pretreatment conditions, a standard curve was designed and constructed for PMA-qPCR detection (y = -3.391x + 36.28; R2 = 0.99). The amplification efficiency reached 97%, and the lowest detection limit of viable cells was approximately 2 × 102 CFU·mL-1. The feasibility of the PMA-qPCR method was confirmed through a manually simulated viable/dead cell assay under various concentrations. The analysis of potato tubers and cucumber seeds revealed that nine naturally collected seed samples contained a range from 102 to 104 CFU·g-1 viable Pbr bacteria. Furthermore, the system effectively identified changes in the number of pathogenic bacteria in cucumber and potato leaves affected by soft rot throughout the disease period. Overall, the detection and prevention of bacterial soft rot caused by Pbr is crucial.

Exploring the Biologically Active Metabolites Produced by Bacillus cereus for Plant Growth Promotion, Heat Stress Tolerance, and Resistance to Bacterial Soft Rot in Arabidopsis

Eight gene clusters responsible for synthesizing bioactive metabolites associated with plant growth promotion were identified in the Bacillus cereus strain D1 (BcD1) genome using the de novo whole-genome assembly method. The two largest gene clusters were responsible for synthesizing volatile organic compounds (VOCs) and encoding extracellular serine proteases. The treatment with BcD1 resulted in an increase in leaf chlorophyll content, plant size, and fresh weight in Arabidopsis seedlings. The BcD1-treated seedlings also accumulated higher levels of lignin and secondary metabolites including glucosinolates, triterpenoids, flavonoids, and phenolic compounds. Antioxidant enzyme activity and DPPH radical scavenging activity were also found to be higher in the treated seedlings as compared with the control. Seedlings pretreated with BcD1 exhibited increased tolerance to heat stress and reduced disease incidence of bacterial soft rot. RNA-seq analysis showed that BcD1 treatment activated Arabidopsis genes for diverse metabolite synthesis, including lignin and glucosinolates, and pathogenesis-related proteins such as serine protease inhibitors and defensin/PDF family proteins. The genes responsible for synthesizing indole acetic acid (IAA), abscisic acid (ABA), and jasmonic acid (JA) were expressed at higher levels, along with WRKY transcription factors involved in stress regulation and MYB54 for secondary cell wall synthesis. This study found that BcD1, a rhizobacterium producing VOCs and serine proteases, is capable of triggering the synthesis of diverse secondary metabolites and antioxidant enzymes in plants as a defense strategy against heat stress and pathogen attack.