Abstract
Salt stress is an adverse environmental factor for plant growth and development. Under salt stress, plants can activate the selective autophagy pathway to alleviate stress. However, the regulatory mechanism of selective autophagy in response to salt stress remains largely unclear. Here, we report that the selective autophagy receptor PagNBR1 (neighbor of BRCA1) is induced by salt stress in Populus. Overexpression of PagNBR1 in poplar enhanced salt stress tolerance. Compared with wild type (WT) plants, the transgenic lines exhibited higher antioxidant enzyme activity, less reactive oxygen species (ROS), and higher net photosynthesis rates under salt stress. Furthermore, co-localization and yeast two-hybrid analysis revealed that PagNBR1 was localized in the autophagosome and could interact with ATG8 (autophagy-related gene). PagNBR1 transgenic poplars formed more autophagosomes and exhibited higher expression of ATG8, resulting in less accumulation of insoluble protein and insoluble ubiquitinated protein compared to WT under salt stress. The accumulation of insoluble protein and insoluble ubiquitinated protein was similar under the treatment of ConA in WT and transgenic lines. In summary, our results imply that PagNBR1 is an important selective autophagy receptor in poplar and confers salt tolerance by accelerating antioxidant system activity and autophagy activity. Moreover, the NBR1 gene is an important potential molecular target for improving stress resistance in trees.
Highlights
Soil salinity is an adverse environmental factor, which has a serious impact on plant growth, development, and productivity (Zorb et al, 2005)
Multiple sequence alignment analysis revealed that the protein sequence shares 42.1% identity with AtNBR1 protein and 96.6% identify with neighbor of BRCA1 gene 1 (NBR1) protein from P. trichocarpa (PtrNBR1)
To clarify whether autophagy is induced under salt stress, the transcriptional level of ATG3, ATG7, and Autophagy-related gene 8 (ATG8) (a-g) genes were used to evaluate whether autophagy was induced under stress conditions (Figures 7H–J; Supplementary Figure S8) and the results showed that autophagy-related genes (ATG) genes (ATG8a-g, ATG3, and ATG7) increased to different degrees in wild type (WT) and transgenic plants after salt stress compared with the control group
Summary
Soil salinity is an adverse environmental factor, which has a serious impact on plant growth, development, and productivity (Zorb et al, 2005). An important strategy for plants to cope with salt stress is to maintain the water potential and K+/Na+ homeostasis by synthesizing several classes of osmolytes (e.g., proline, polyamine, and sugar alcohol) and regulating the activity of ion channel proteins, such as SOS1 (Deinlein et al, 2014; Yang and Guo, 2018). Another important strategy is scavenging reactive oxygen species through the antioxidant system, such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate-glutathione (AsA-GSH) cycle (Raja et al, 2017; Yang and Guo, 2018)
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