Organic acid metabolites involved in local adaptation to altitudinal gradient in Agriophyllum squarrosum, a desert medicinal plant.

Agriophyllum squarrosum (L.) Moq., a pioneer plant endemic to the temperate deserts of Asia, could be domesticated into an ideal crop with outstanding ecological and medicinal characteristics. A previous study showed differential organic acid accumulation between two in situ altitudinal ecotypes. To verify whether this accumulation was determined by environmental or genetic factors, we conducted organic acid targeted metabolic profiling among 14 populations of A. squarrosum collected from regions with different altitudes based on a common garden experiment. Results showed that the most abundant organic acid in A. squarrosum was citric acid (96.03%, 2322.90 μg g-1). Association analysis with in situ environmental variables showed that salicylic acid content was positively correlated with altitudinal gradient. Considering the enrichment of salicylic acid and protocatechualdehyde in high-altitude populations based on the common garden experiment, and the high expression of their biosynthesis relative genes (i.e., PAL and C4H) in the in situ high-altitude ecotype, we propose that organic acid accumulation could be involved in local adaptation to high altitudes. This study not only addresses the molecular basis of local adaptation involving the accumulation of organic acids in the desert plant A. squarrosum but also provides a method to screen wild germplasms to mitigate the impact of global climate change.