Abstract
The dirigent (DIR and DIR-like) proteins involved in lignification, play a pivotal role against biotic and abiotic stresses in plants. However, no information is available about DIR gene family in pepper (Capsicum annuum L.). In this study, 24 putative dirigent genes (CaDIRs) were identified, their gene structure, genome location, gene duplication and phylogenetic relationship were elucidated. Tissue-specific expression analysis displayed the highest transcription levels in flower, stem and leaf. Some CaDIRs were up-regulated by virulent (CaDIR2, 3, 6, 7, 11, 14, 16, 22 and 23) and avirulent (CaDIR3, 5, 7, 16, 20, 22, 23 and 24) Phytophthora capsici strains, as well as by Methyl jasmonate, salicylic acid, NaCl and mannitol stresses. Acid-soluble lignin content increased (103.21%) after P. capsici inoculation (48-hour). Silencing of CaDIR7 weakened plant defense by reducing (~50%) root activity and made plants more susceptible (35.7%) to P. capsici and NaCl (300 mM). Leaf discs of the CaDIR7:silenced plants exposed to NaCl and mannitol (300 mM each), exhibited a significant decrease (56.25% and 48% respectively) in the chlorophyll content. These results suggested that CaDIR7 is involved in pepper defense response against pathogen and abiotic stresses and the study will provide basic insights for future research regarding CaDIRs.
Highlights
Pepper (Capsicum annuum L.) is an important solanaceous vegetable worldwide
In the case of Zunla-1, out of 25 genes, the single gene (Capana01g000149) sequence exhibited poor identification with CM334 (CA01g01690). When this was used as a query to blast in NCBI Conserved Domain Database (CDD), its domain (Uncharacterized protein family UPF0016) was found to be other than dirigent
The silencing efficiency of CaDIR7 was investigated through a qRT-PCR analysis, and the results showed that the expression levels of CaDIR7 gene in the silenced plants were much lower than in the control plants (Fig. 10B)
Summary
Pepper (Capsicum annuum L.) is an important solanaceous vegetable worldwide. Many vegetables are affected by the oomycete pathogen P. capsici, which has been reported to infest pepper, eggplant, tomato, all cucurbits, and more recently snap and limabeans[1,2]. DIR proteins from Forsythia suspensa[13], Podophyllum peltatum[14], and Thuja plicata (western red cedar)[15] are biochemically involved in directing the stereo-specific coupling of E-coniferyl alcohol to produce the lignan ( + )-pinoresinol. Based on this activity and its associated cellular localization in F. intermedia, DIR proteins could function in the formation of lignin[16]. The current study will provide a basis for the role of CaDIRs in pepper defense response against P. capsici and abiotic stresses and future insights for research on the DIR gene family
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