Abstract
Plant often responds to fungal pathogens by expressing a group of proteins known as pathogenesis-related proteins (PRs). The expression of PR is mediated through pathogen-induced signal-transduction pathways that are fine-tuned by phytohormones such as methyl jasmonate (MeJA). Here, we report functional characterization of an Ocimum basilicum PR5 family member (ObTLP1) that was identified from a MeJA-responsive expression sequence tag collection. ObTLP1 encodes a 226 amino acid polypeptide that showed sequence and structural similarities with a sweet-tasting protein thaumatin of Thaumatococcus danielli and also with a stress-responsive protein osmotin of Nicotiana tabacum. The expression of ObTLP1 in O. basilicum was found to be organ-preferential under unstressed condition, and responsive to biotic and abiotic stresses, and multiple phytohormone elicitations. Bacterially-expressed recombinant ObTLP1 inhibited mycelial growth of the phytopathogenic fungi, Scleretonia sclerotiorum and Botrytis cinerea; thereby, suggesting its antifungal activity. Ectopic expression of ObTLP1 in Arabidopsis led to enhanced tolerance to S. sclerotiorum and B. cinerea infections, and also to dehydration and salt stress. Moreover, induced expression of the defense marker genes suggested up-regulation of the defense-response pathways in ObTLP1-expressing Arabidopsis upon fungal challenge. Thus, ObTLP1 might be useful for providing tolerance to the fungal pathogens and abiotic stresses in crops.
Highlights
Pathway[20,21]
The analysis revealed increased transcript level of the ObTLP1 in methyl jasmonate (MeJA)-treated O. basilicum compared to the control, at 3 hr to 24 hr after treatment with 250 μ M MeJA (Fig. 1A)
Further to test whether ObTLP1 is responsive to other phytohormone elicitations, the transcript expression pattern of the ObTLP1 was determined in O. basilicum after treatments with salicylic acid (SA), abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of the ET (Fig. 1B–D)
Summary
Besides providing defense against pathogenic fungi, TLPs might help plants to mitigate various abiotic stresses[9,18,22,23]. Phytohormones methyl jasmonate (MeJA), ethylene (ET) and salicylic acid (SA) are the primary mediators of plant defense response towards attack by fungal pathogens[2]. The expression of PRs has been shown to induce when plants are externally treated with phytohormones or exposed to different biotic and abiotic stress conditions[8,9,29,30]. We report detailed analysis and functional characterization of an O. basilicum PR5 family member (ObTLP1) following bacterial and plant expressions. Ectopic expression of ObTLP1 in Arabidopsis thaliana led to enhanced tolerance to the fungal pathogens and to abiotic stresses
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