Objective To investigate the role of asparagine-rich protein (NRP) in resistance of Arabidopsis thaliana to radiation.

Methods Wild-type (WT), NRP overexpression lines (Pro35S:NRP-GFP), and NRP mutant lines (nrp) of A. thaliana seeds were used and divided into two groups: irradiation (120 Gy γ-ray irradiation) and control (no irradiation). (1) Seeds of three genotypes of A. thaliana were cultured to the third day and irradiated with 120 Gy; the root length of each group was measured after culture was continued to the seventh day. (2) The seeds of three genotypes of A. thaliana were cultured in MS medium to the seventh day, and then irradiated with 120 Gy. After irradiation, the seeds were transplanted to the substrate soil for further culture until the 30th day. The growth and morphology of each group of plants were observed. (3) WT A. thaliana seeds were cultured to the seventh day and irradiated with 120 Gy. After 24 h, the changes in the relative expression of NRP and poly-ADP-ribose polymerase 2 (PARP2) genes in WT plants before and after irradiation were analyzed by real-time quantitative PCR. (4) The seeds of Pro35S:NRP-GFP A. thaliana were cultured to the seventh day and then irradiated with 120 Gy. The seedlings were observed by fluorescence confocal microscopy at different times after irradiation. Independent sample t-test was used for comparison between groups.

Results (1) After irradiation, the root lengths of WT and nrp A. thaliana were significantly shortened (t=9.212 and 6.490, both P=0.000) to (2.73±0.43) cm and (1.31±0.53) cm, respectively, whereas the root lengths of the control group were (4.56±0.41) cm and (2.89±0.60) cm. The root lengths of Pro35S:NRP-GFP with or without irradiation exhibited no significant changes ((3.01±0.34) cm vs. (2.96±0.34) cm, t=0.253, P=0.801). (2) The growth and development of WT and nrp A. thaliana were significantly reduced (t=6.361–12.250, all P=0.000), whereas that of Pro35S:NRP-GFP maintained its development after irradiation. (3) The relative expression of NRP and PARP2 of WT A. thaliana significantly increased after irradiation (t=4.447 and 7.776, P=0.002 and 0.000). (4) Pro35S:NRP-GFP seedlings exhibited NRP re-localization into the nucleus after irradiation at each time point.

Conclusion NRP may play a critical role in the resistance of A. thaliana to radiation, suggesting that NRP may be an important gene in radiation-caused injury in this species.