Identification of the interacting proteins of Bambusa pervariabilis × Dendrocalamopsis grandis in response to the transcription factor ApCtf1β in Arthrinium phaeospermum

Targeting of the Hybrid Bamboo BDDnaJ by Pathogen Effector ApcE12 Regulates the Unfolded Protein Response

The shoot blight disease of Bambusa pervariabilis × Dendrocalamopsis grandis, caused by Arthrinium phaeospermum, threatens bamboo's ecological and economic value. This study explores the pathogenic effector ApcE12's role in modulating plant immunity through interactions with the host proteins BDClp and BDDnaJ. ApcE12 directly interacts with BDDnaJ, a vital regulator of the unfolded protein response (UPR), as validated through yeast two-hybrid, bimolecular fluorescence complementation, and GST pull-down assays. Functional analyses demonstrated that silencing BDDnaJ reduces UPR, activating programmed cell death (PCD) and blocking further pathogen infection to enhance plant resistance. BDDnaJ was found to regulate BDBiP protein stability by interacting with BDBiP, and it is this mechanism by which the pathogenic effector ApcE12 regulates BDDnaJ expression, enhances UPR signalling, and inhibits PCD, thereby promoting infection. These findings deepen our understanding of how fungal effectors manipulate UPR and PCD to overcome plant defences, providing novel insights for developing resistance strategies in bamboo species.

Functional characterization of cutinase genes NsCut1-NsCut4 in Neostagonosporella sichuanensis and their effects on fishscale bamboo

Fishscale bamboo rhombic-spot, caused by Neostagonosporella sichuanensis, poses a significant threat to Phyllostachys heteroclada in Sichuan province. Based on genomic analysis, four cutinase genes, NsCut1-NsCut4, were identified, cloned, and functionally validated. Bioinformatics analyses revealed that the proteins encoded by these genes possess secretory functions, lack transmembrane domains, and contain conserved cutinase domains highly homologous to those in other fungi. Recombinant proteins expressed via a prokaryotic system exhibited strong hydrolytic activity against glycerol tributyrate and bamboo white cream at 40°C and pH 8.0, while signal peptide and subcellular localization analyses confirmed their secretory function and localization to the cell wall. Gene knockout experiments were performed to construct deletion strains ΔNsCut and corresponding complemented strains ΔNsCut+. Notably, ΔNsCut1 and ΔNsCut3 resulted in reduced pigmentation, decreased spore production, and increased sensitivity to NaCl, H2O2, and Congo red, along with reduced pathogenicity-indicating that these genes play key roles in metabolic and reproductive processes, oxidative stress responses, and the maintenance of cell wall integrity. In contrast, ΔNsCut2 and ΔNsCut4 did not exhibit significant differences compared to the wild type. This work advances our understanding of the role of cutinases in the pathogenic interaction between N. sichuanensis and P. heteroclada, providing a theoretical basis for further exploration of the pathogen's underlying mechanisms.

Genome-wide identification of short-chain dehydrogenases/reductases genes and functional characterization of ApSDR53C2 in melanin biosynthesis in Arthrinium phaeospermum

Introduction

Arthrinium phaeospermum can cause large areas wilted and death of Bambusa pervariabilis × Dendrocalamopsis grandis, resulting in serious ecological and economic losses. Previous studies found that the appressorium of A. phaeospermum must form to invade the host cells and cause disease. A short-chain dehydrogenase/reductase gene has been shown to maintain the osmotic pressure of the appressorium by synthesizing fungal melanin to penetrate the plant epidermis and cause disease. The SDR gene family of A. phaeospermum was found to be highly expressed during the penetration in the transcriptome sequencing results. Still, the relationship with melanin biosynthesis of A. phaeospermum is not clear.

Methods

We aimed to predict the biological function of the SDR gene family in A. phaeospermum, identify key ApSDR genes with pathogenic roles, and explore the pathogenic mechanism. We have characterized the SDR family of A. pheospermum bioinformatically. Candidate ApSDRs screened by transcriptome sequencing were compared by qPCR experiments to obtain key ApSDRs that may play an important role in infestation and adversity resistance. Knockout mutants, the co-knockout mutant, and backfill mutants of key ApSDRs were obtained for phenotypic and stress conditions analysis. We explored and validated the pathogenic mechanisms through cellulose membrane penetration experiments and analysis of melanin-related gene synthesis levels.

Results and discussion

180 ApSDRs were identified bioinformatically. After screening six candidate ApSDRs with noticeably elevated expression using transcriptome sequencing, qPCR experiments revealed that ApSDR53C2 and ApSDR548U2 had the highest expression. The results of phenotypic and stress conditions analysis indicate that ApSDRs are critical for the growth, development, stress response, and fungicide resistance of A. phaeospermum. The pathogenicity analysis revealed that ApSDR53C2 and ApSDR548U2 play important roles in virulence, with ApSDR53C2 having a stronger effect. A comparison of melanin synthesis levels between wild-type and ΔApSDR53C2 strains showed that ApSDR53C2 positively regulates melanin biosynthesis to promote penetration. The findings demonstrate that ApSDRs are essential for A. phaeospermum to withstand stress and facilitate melanin biosynthesis, which in turn contributes to its virulence.

The Targeted Regulation of BDUbc and BDSKL1 Enhances Resistance to Blight in Bambusa pervariabilis × Dendrocalamopsis grandis

Arthrinium phaeospermum is the major pathogen responsible for the significant stem disease "blight" in B. pervariabilis × D. grandis. The interacting proteins of the key pathogenic factor ApCtf1β, BDUbc and BDSKL1, have previously been obtained by two-hybrid, BiFC, GST pull-down yeast assays. However, the functions of these interacting proteins remain unknown. This study successfully obtained transgenic plants overexpressing BDUbc, BDSKL1, and BDUbc + BDSKL1 via Agrobacterium-mediated gene overexpression. qRT-PCR analysis revealed significantly increased expression levels of BDUbc and BDSKL1 in the transgenic plants. After infection with the pathogenic spore suspension, the disease incidence and severity index significantly decreased across all three transgenic plants, accompanied by a marked increase in defense enzyme levels. Notably, the co-transformed plant, OE-BDUbc + BDSKL1, demonstrated the lowest disease incidence and severity index among the transgenic variants. These results not only indicate that BDUbc and BDSKL1 are disease-resistant genes, but also that these two genes may exhibit a synergistic enhancement effect, which further improves the resistance to blight in Bambusa pervariabilis × Dendrocalamopsis grandis.

Interaction between SlMAPK3 and SlASR4 regulates drought resistance in tomato (Solanum lycopersicum L.)

Tomato is a leading vegetable in modern agriculture, and with global warming, drought has become an important factor threatening tomato production. Mitogen-activated protein kinase 3 (MAPK3) plays an important role in plant disease and stress resistance. To clarify the downstream target proteins of SlMAPK3 and the mechanism of stress resistance in tomato, this study was conducted with the SlMAPK3-overexpressing lines OE-1 and OE-2 and the CRISPR/Cas9-mediated mutant lines slmapk3-1 and slmapk3-2 under PEG 6000-simulated drought. The results of yeast two-hybrid (Y2H), pull-down, and coimmunoprecipitation (Co-IP) assays confirmed that SlASR4 (NP_001269248.1) interacted with SlMAPK3. Analyses of the SlASR4 protein structure and SlASR4 expression under PEG 6000 and BTH stress revealed that SlASR4 has a highly conserved protein structural domain involved in the drought stress response under PEG 6000 treatment. The function of the SlASR4 and SlMAPK3 downstream target protein, in drought resistance in tomato plants, was identified by virus-induced gene silencing (VIGS). This study clarified that SlMAPK3 interacts with SlASR4 to positively regulate drought resistance in tomato plants.

Identification and Characterization of the BBX Gene Family in Bambusa pervariabilis × Dendrocalamopsis grandis and Their Potential Role under Adverse Environmental Stresses

Zinc finger protein (ZFP) transcription factors play a pivotal role in regulating plant growth, development, and response to biotic and abiotic stresses. Although extensively characterized in model organisms, these genes have yet to be reported in bamboo plants, and their expression information is lacking. Therefore, we identified 21 B-box (BBX) genes from a transcriptome analysis of Bambusa pervariabilis × Dendrocalamopsis grandis. Consequently, multiple sequence alignments and an analysis of conserved motifs showed that they all had highly similar structures. The BBX genes were divided into four subgroups according to their phylogenetic relationships and conserved domains. A GO analysis predicted multiple functions of the BBX genes in photomorphogenesis, metabolic processes, and biological regulation. We assessed the expression profiles of 21 BBX genes via qRT-PCR under different adversity conditions. Among them, eight genes were significantly up-regulated under water deficit stress (BBX4, BBX10, BBX11, BBX14, BBX15, BBX16, BBX17, and BBX21), nine under salt stress (BBX2, BBX3, BBX7, BBX9, BBX10, BBX12, BBX15, BBX16, and BBX21), twelve under cold stress (BBX1, BBX2, BBX4, BBX7, BBX10, BBX12, BBX14, BBX15, BBX17, BBX18, BBX19, and BBX21), and twelve under pathogen infestation stress (BBX1, BBX2, BBX4, BBX7, BBX10, BBX12, BBX14, BBX15, BBX17, BBX18, BBX19, and BBX21). Three genes (BBX10, BBX15, and BBX21) were significantly up-regulated under both biotic and abiotic stresses. These results suggest that the BBX gene family is integral to plant growth, development, and response to multivariate stresses. In conclusion, we have comprehensively analyzed the BDBBX genes under various adversity stress conditions, thus providing valuable information for further functional studies of this gene family.

Verification of the Interaction Target Protein of the Effector ApCE22 of Arthrinium phaeospermum in Bambusa pervariabilis × Dendrocalamopsis grandis

The study of interaction proteins of the pathogen A. phaeospermum effector protein is an important means to analyze the disease-resistance mechanism of Bambusa pervariabilis × Dendrocalamopsis grandis shoot blight. To obtain the proteins interacting with the effector ApCE22 of A. phaeospermum, 27 proteins interacting with the effector ApCE22 were initially identified via a yeast two-hybrid assay, of which four interaction proteins were obtained after one-to-one validation. The B2 protein and the chaperone protein DnaJ chloroplast protein were then verified to interact with the ApCE22 effector protein by bimolecular fluorescence complementation and GST pull-down methods. Advanced structure prediction showed that the B2 protein contained the DCD functional domain related to plant development and cell death, and the DnaJ protein contained the DnaJ domain related to stress resistance. The results showed that both the B2 protein and DnaJ protein in B. pervariabilis × D. grandis were the target interaction proteins of the ApCE22 effector of A. phaeospermum and related to the stress resistance of the host B. pervariabilis × D. grandis. The successful identification of the pathogen effector interaction target protein in B. pervariabilis × D. grandis plays an important role in the mechanism of pathogen–host interaction, thus providing a theoretical basis for the control of B. pervariabilis × D. grandis shoot blight.