Comparative Analysis of Alternative Splicing in Two Contrasting Apple Cultivars Defense against Alternaria alternata Apple Pathotype Infection

Inhibitory effect of benzocaine from Schisandra chinensis on Alternaria alternata

The clinical effects of Schisandra chinensis against human disease are well-documented; however, studies on its application in controlling plant pathogens are limited. Here, we investigated its inhibitory effect on the growth of Alternaria alternata, a fungus which causes significant post-harvest losses on apples, known as black spot disease. S. chinensis fruit extract exhibited strong inhibitory effects on the growth of A. alternata with an EC50 of 1882.00 mg/L. There were 157 compounds identified in the extract by high performance liquid chromatography-mass spectrometry, where benzocaine constituted 14.19% of the extract. Antifungal experiments showed that the inhibitory activity of benzocaine on A. alternata was 43.77-fold higher than the crude extract. The application of benzocaine before and after A. alternata inoculation on apples prevented the pathogen infection and led to mycelial distortion according to scanning electron microscopy. Transcriptome analysis revealed that there were 4226 genes differentially expressed between treated and untreated A. alternata-infected apples with benzocaine. Metabolomics analysis led to the identification of 155 metabolites. Correlation analysis between the transcriptome and metabolome revealed that benzocaine may inhibit A. alternata growth via the beta-alanine metabolic pathway. Overall, S. chinensis extract and benzocaine are environmentally friendly plant-based fungicides with potential to control A. alternata.

Transcriptome analyses reveal key roles of alternative splicing regulation in atlantic salmon during the infectious process of Piscirickettsiosis disease

In the Chilean salmon farming industry, infection by Piscirickettsia salmonis is the primary cause of the main bacterial disease known as Piscirickettsiosis, which has an overwhelming economic impact. Although it has been demonstrated that Piscirickettsiosis modifies the expression of numerous salmonids genes, it is yet unknown how alternative splicing (AS) contributes to salmonids bacterial infection. AS, has the potential to create heterogeneity at the protein and RNA levels and has been associated as a relevant molecular mechanism in the immune response of eukaryotes to several diseases. In this study, we used RNA data to survey P. salmonis-induced modifications in the AS of Atlantic salmon and found that P. salmonis infection promoted a substantial number (158,668) of AS events. Differentially spliced genes (DSG) sensitive to Piscirickettsiosis were predominantly enriched in genes involved in RNA processing, splicing and spliceosome processes (e.g., hnRNPm, hnRPc, SRSF7, SRSF45), whereas among the DSG of resistant and susceptible to Piscirickettsiosis, several metabolic and immune processes were found, most notably associated to the regulation of GTPase, lysosome and telomere organization-maintenance. Furthermore, we found that DSG were mostly not differentially expressed (5-7 %) and were implicated in distinct biological pathways. Therefore, our results underpin AS achieving a significant regulatory performance in the response of salmonids to Piscirickettsiosis.

Deciphering the role of alternative splicing as modulators of defense response in the MYMIV- Vigna mungo pathosystem

Alternative splicing (AS) is a crucial regulatory mechanism that impacts transcriptome and proteome complexity under stressful situations. Although its role in abiotic stresses is somewhat understood, our understanding of the mechanistic regulation of pre-mRNA splicing in plant-pathogen interaction is meagre. To comprehend this unexplored immune reprogramming mechanism, transcriptome profiles of Mungbean Yellow Mosaic India Virus (MYMIV)-resistant and susceptible Vigna mungo genotypes were analysed for AS genes that may underlie the resistance mechanism. Results revealed a repertoire of AS-isoforms accumulated during pathogenic infestation, with intron retention being the most common AS mechanism. Identification of 688 differential alternatively spliced (DAS) genes in the resistant host elucidates its robust antiviral response, whereas 322 DAS genes were identified in the susceptible host. Enrichment analyses confirmed DAS transcripts pertaining to stress, signalling, and immune system pathways have undergone maximal perturbations. Additionally, a strong regulation of the splicing factors has been observed both at transcriptional and post-transcriptional levels. qPCR validation of candidate DAS transcripts with induced expression upon MYMIV-infection demonstrated a competent immune response in the resistant background. The AS-impacted genes resulted either in partial/complete loss of functional domains or altered sensitivity to miRNA-mediated gene silencing. A complex regulatory module, miR7517-ATAF2, has been identified in an aberrantly spliced ATAF2 isoform that exposes an intronic miR7517 binding site, thereby suppressing the negative regulator to enhance defense reaction. The present study establishes AS as a non-canonical immune reprogramming mechanism that operates in parallel, thereby offering an alternative strategy for developing yellow mosaic-resistant V. mungo cultivars. This article is protected by copyright. All rights reserved.

Metabolomic profiling and its association with the bio-efficacy of Aspergillus niger strain against Fusarium wilt of guava

Bio-control agents are the best alternative to chemicals for the successful management of plant diseases. The fungus Aspergillus niger is known to produce diverse metabolites with antifungal activity, attracting researchers to exploit it as a bio-control agent for plant disease control. In the present study, 11 A. niger strains were isolated and screened for their antagonism against the guava wilt pathogen under in vitro and in planta conditions. Strains were identified morphologically and molecularly by sequencing the internal transcribed spacer (ITS), β-tubulin, and calmodulin genes. The strains were evaluated through dual culture, volatile, and non-volatile methods under an in vitro study. AN-11, AN-6, and AN-2 inhibited the test pathogen Fusarium oxysporum f. sp. psidii (FOP) at 67.16%, 64.01%, and 60.48%, respectively. An in planta study was conducted under greenhouse conditions with 6 months old air-layered guava plants (var. Allahabad Safeda) by pre- and post-inoculation of FOP. The AN-11 strain was found to be effective under both pre- and post-inoculation trials. Furthermore, gas chromatography-mass spectrometry (GC-MS) analysis was carried out to characterize the volatile compounds of the most potential strain, A. niger. The hexane soluble fraction showed the appearance of characteristic peaks of hexadecenoic acid methyl ester (4.41%), 10-octadecanoic acid methyl ester (3.79%), dodecane (3.21%), undecane (3.19%), gibepyrone A (0.15%), 3-methylundecane (0.36%), and citroflex A (0.38%). The ethyl acetate fraction of the bio-control fungi revealed the occurrence of major antifungal compounds, such as acetic acid ethyl ester (17.32%), benzopyron-4-ol (12.17%), 1,2,6-hexanetriol (7.16%), 2-propenoic acid ethanediyl ester (2.95%), 1-(3-ethyloxiranyl)-ethenone (0.98%), 6-acetyl-8-methoxy dimethyl chromene (0.96%), 4-hexyl-2,5-dihydro dioxo furan acetic acid (0.19%), and octadecanoic acid (1.11%). Furthermore, bio-control abilities could be due to hyper-parasitism, the production of secondary metabolites, and competition for sites and nutrients. Indeed, the results will enrich the existing knowledge of metabolomic information and support perspectives on the bio-control mechanism of A. niger.