Arabidopsis Plants Having Defects in Nonsense-mediated mRNA Decay Factors UPF1, UPF2, and UPF3 Show Photoperiod-dependent Phenotypes in Development and Stress Responses

Nonsense-mediated mRNA decay (NMD) is an important mRNA quality surveillance pathway in all eukaryotes that eliminates aberrant mRNAs derived from various sources. Three NMD factor proteins, UPF1, UPF2, and UPF3 are required for the NMD process and were found to be also involved in certain stress responses in mammalian and yeast cells. Using Arabidopsis thaliana mutants of UPF1 and UPF3 and UPF2-silenced lines (irUPF2), we examined the involvement of UPF1, UPF2, and UPF3 in development and in response to stresses, wounding and infection by Pseudomonas syringae pv. tomato strain DC3000. Under the long (16 h) photoperiod condition, Arabidopsis having a defect in NMD factors exhibited altered morphologies of various organs, disturbed homeostasis of wounding-induced jasmonic acid and pathogen-elicited salicylic acid, and abnormal wounding- and methyl jasmonate-induced changes in the transcript levels of two defense-related genes, LOX2 and VSP2. Importantly, when plants were cultivated under the short (10 h) photoperiod condition, mutants of UPF1 and UPF3 and irUPF2 showed smaller differences from the wild-type plants in growth and stress-induced responses. These data suggest a complex regulatory network, likely composed of light signaling and NMD factor-mediated pathways, in influencing plant development and adaption to environmental stresses.