Functional analysis of DA1-Related Protein 2 in Arabidopsis under salt stress

Salt stress inhibits plant growth and development, resulting in low crop yield. Therefore, the mechanism of plant response to salt stress has received much attention in plant science research. Early development (including seed germination and greening) is not only critical for seedling establishment and subsequent plant growth and development, but is also more sensitive to salt stress. However, the molecular mechanisms underlying plant salt tolerance during this developmental stage has remained largely unknown. In this study, we identified a gene, DAR2 (DA1-Related Protein 2), which regulated primary root growth by map-based cloning in Arabidopsis. We noted that DAR2 gene was induced by 200 mmol·L^-1 NaCl in 10-day-old Col-0 seedlings. GUS staining showed that the expression of pDAR2::GUS was altered, suggesting that DAR2 gene was induced in root tip and leaf apex phloem. We counted the Col-0 and dar2-3 seed germination and greening rates in different MS medium - 0 (CK), 100 mmol·L^-1 NaCl, 150 mmol·L^-1 NaCl, 200 mmol·L^-1 NaCl, 150 mmol·L^-1 KCl and 200 mmol·L^-1 mannitol. These results showed that compared with the wild type, either seed germination or greening of dar2-3 mutant obviously delayed with gradual increase in NaCl concentration. Under 150 mmol·L^-1 KCl and 200 mmol·L^-1 mannitol treatments, dar2-3 mutant seed germination and greening delayed in relation to the wild type. Interestingly, the mutant exhibited increased sensitivity to NaCl, KCl and mannitol treatments during seed germination and greening compared with the wild type. These results suggested that while DAR2 was effective in mediating plant response to general osmotic stress, it was not specific to ion stress in the early growth and development phase. Our findings provided novel insights into salt tolerance and enhanced crop resistance to salt stress.