Abstract
Nudix hydrolases comprise a large gene family of twenty nine members in Arabidopsis, each containing a conserved motif capable of hydrolyzing specific substrates like ADP-glucose and NADH. Until now only two members of this family, AtNUDX6 and AtNUDX7, have been shown to be involved in plant immunity. RPP4 is a resistance gene from a multigene family that confers resistance to downy mildew. A time course expression profiling after Hyaloperonospora arabidopsidis inoculation in both wild-type (WT) and the rpp4 mutant was carried out to identify differentially expressed genes in RPP4-mediated resistance. AtNUDX8 was one of several differentially expressed, downregulated genes identified. A T-DNA knockout mutant (KO-nudx8) was obtained from a Salk T-DNA insertion collection, which exhibited abolished AtNUDX8 expression. The KO-nudx8 mutant was infected separately from the oomycete pathogen Hpa and the bacterial pathogen Pseudomonas syringae pv. maculicola ES4326. The mutant displayed a significantly enhanced disease susceptibility to both pathogens when compared with the WT control. We observed a small, stunted phenotype for KO-nudx8 mutant plants when grown over a 12/12 hour photoperiod but not over a 16/8 hour photoperiod. AtNUDX8 expression peaked at 8 hours after the lights were turned on and this expression was significantly repressed four-fold by salicylic acid (SA). The expression of three pathogen-responsive thioredoxins (TRX-h2, TRX-h3 and TRX-h5) were downregulated at specific time points in the KO-nudx8 mutant when compared with the WT. Furthermore, KO-nudx8 plants like the npr1 mutant, displayed SA hypersensitivity. Expression of a key SA biosynthetic gene ICS1 was repressed at specific time points in the KO-nudx8 mutant suggesting that AtNUDX8 is involved in SA signaling in plants. Similarly, NPR1 and PR1 transcript levels were also downregulated at specific time points in the KO-nudx8 mutant. This study shows that AtNUDX8 is involved in plant immunity as a positive regulator of defense in Arabidopsis.
Highlights
Plants are sessile organisms that evolved remarkable signaling pathways in order to cope with several abiotic and biotic stresses such as pathogen attack
In order to identify genes involved in RPP4-mediated resistance against Hyaloperonospora arabidopsidis (Hpa) Emwa1, a time course gene expression profiling was performed after Hpa infiltration (0 hour, 2 days post-infiltration, 4 dpi and 6 dpi) for the rpp4 mutant and WT
The evening element is known to be regulated by the CIRCADIAN CLOCKASSOCIATED 1 gene (CCA1), and the fact the EE can be found in the promoter region of some defense genes suggests a link between the circadian clock and plant defense
Summary
Plants are sessile organisms that evolved remarkable signaling pathways in order to cope with several abiotic and biotic stresses such as pathogen attack. In one branch of the plant immune system there are nucleotide binding leucine-rich repeat (NB-LRR) proteins in the cell that recognize a plethora of pathogen effectors from several kingdoms and activate a cascade of signaling pathways leading to effector triggered immunity (ETI) [1, 2]. Some plant immune responses are associated with NPR1 protein conformational changes induced by redox levels [4]. NPR1 is a well-known master regulator of pathogenesis related (PR) gene expression and salicylic acid (SA) signaling [5, 6]. NPR1 protein resides in the cytoplasm as an oligomer maintained by disulphide bonds that are sensitive to redox changes [4]. Reduction of disulphide bonds cause NPR1 monomer migration to the nucleus and activation of PR gene expression. NPR1 works upstream of SA suppressing expression of ICS1 and inhibiting SA biosynthesis in a negative feedback loop [7]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
