Defense responses to Fusarium oxysporum f. sp. ricini infection in castor (Ricinus communis L.) cultivars

Gene markers generating polygenic resistance in melon-Fusarium wilt-FOM1.2 interaction pathosystem

Developing melon genotypes with resistance to Fusarium oxysporum f. sp. Melonis-(FOM) race1.2 is a major goal in any breeding program. In this study, we identified the role of 11 gene markers that contribute to polygenic resistance during the FOM1.2-melon interaction. qRT-PCR analysis elucidated upregulation of candidate marker genes AMT, DXPR, Fom-2, GLUC, GalS, GRF3, MLO, PRK, RuBlsCo, TLP and WRKY in resistant 'Shante-F1' and 'Khatouni', and susceptible 'Shante-T' and 'Shahabadi' at 7, 14 and 21 days post-inoculation (dpi). We also studied changes in defence-related enzyme activity: chitinase (CHI), β-1,3-glucanase (GLU) and peroxidase (POX) in melon roots. AMT, GLUC and DXPR transcripts were upregulatied in leaf and root tissues of the resistant 'Shante-F1' and 'Shahabadi'. Transcript levels for GalS and GRF3 increased 6.77- and 6.83-fold in roots of 'Shante-F1' at 7 dpi, whereas in PRK, TLP and WRKY theye increased by 7.84-, 5.15- and 12.26-fold at 14 dpi, respectively. However, transcript levels increased by 5.18-fold for Fom-2 and 8.46-fold for MLO at 21 dpi. Also, RBC transcript level peaked at 14 dpi with 4.9-fold increase in leaves of resistant genotypes, whereas AMT increased 2.94-fold at 21 dpi, and GLUC and DXPR increased 7.11- and 2.91-fold at 14 dpi in 'Shante-F', respectively. Defence-related-enzyme activity was also upregulated three-fold in resistant varieties. The dynamic shifts in the melon transcriptome induced by FOM1.2 emphasize that resistance mechanisms are predominantly regulated through signalling pathways involving CHI, GLU, and POX defence response. Surprisingly, the AMT gene, basically resistant to downy mildew, Pseudoperonospora cubensis; GLUC, MLO and PRK resistant to powdery mildew (Sphaerotheca fusca); TLP and WRKY resistant to Phytophthora blight (Phytophthora capsici); and GRF3 and RBC resistant to root knot nematodes (Meloidogyne spp.) were upregulated in resistant genotypes, indicating a dual role of these genes in resistance to more than one disease at a time.

Molecular insights into the jasmonate signaling and associated defense responses against wilt caused by Fusarium oxysporum

Biotic and abiotic stress factors drastically limit plant growth and development as well as alter the physiological, biochemical and cellular processes. This negatively impacts plant productivity, ultimately leading to agricultural and economical loss. Plant defense mechanisms elicited in response to these stressors are crucially regulated by the intricate crosstalk between defense hormones such as jasmonic acid (JA), salicylic acid and ethylene. These hormones orchestrate adaptive responses by modulating the gene regulatory networks leading to sequential changes in the root architecture, cell wall composition, secondary metabolite production and expression of defense-related genes. Fusarium wilt is a widespread vascular disease in plants caused by the soil-borne ascomycete Fusarium oxysporum and is known to attack several economically important plant cultivars. JA along with its conjugated forms methyl jasmonate and jasmonic acid isoleucine critically tunes plant defense mechanisms by regulating the expression of JA-associated genes imparting resistance phenotype. However, it should be noted that some members of F. oxysporum utilize the JA signaling pathway for disease development leading to susceptibility in plants. Therefore, JA signaling pathway becomes one of the important targets amenable for modulation to develop resistance response against Fusarium wilt in plants. In this review, we have emphasized on the physiological and molecular aspects of JA and its significant role in mounting an early defense response against Fusarium wilt disease. Further, utilization of the inherent JA signaling pathway and/or exogenous application of JA in generating Fusarium wilt resistant plants is discussed.

How do plants defend themselves against pathogens-Biochemical mechanisms and genetic interventions

In agro-ecosystem, plant pathogens hamper food quality, crop yield, and global food security. Manipulation of naturally occurring defense mechanisms in host plants is an effective and sustainable approach for plant disease management. Various natural compounds, ranging from cell wall components to metabolic enzymes have been reported to protect plants from infection by pathogens and hence provide specific resistance to hosts against pathogens, termed as induced resistance. It involves various biochemical components, that play an important role in molecular and cellular signaling events occurring either before (elicitation) or after pathogen infection. The induction of reactive oxygen species, activation of defensive machinery of plants comprising of enzymatic and non-enzymatic antioxidative components, secondary metabolites, pathogenesis-related protein expression (e.g. chitinases and glucanases), phytoalexin production, modification in cell wall composition, melatonin production, carotenoids accumulation, and altered activity of polyamines are major induced changes in host plants during pathogen infection. Hence, the altered concentration of biochemical components in host plants restricts disease development. Such biochemical or metabolic markers can be harnessed for the development of "pathogen-proof" plants. Effective utilization of the key metabolites-based metabolic markers can pave the path for candidate gene identification. This present review discusses the valuable information for understanding the biochemical response mechanism of plants to cope with pathogens and genomics-metabolomics-based sustainable development of pathogen proof cultivars along with knowledge gaps and future perspectives to enhance sustainable agricultural production.