Abstract
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 flavonoid accumulation between two in situ altitudinal ecotypes. To verify whether this accumulation was determined by environmental or genetic factors, we conducted flavonoid-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 flavonoid in A. squarrosum was isorhamnetin (48.40%, 557.45 μg/g), followed by quercetin (13.04%, 150.15 μg/g), tricin (11.17%, 128.70 μg/g), isoquercitrin (7.59%, 87.42 μg/g), isovitexin (7.20%, 82.94 μg/g), and rutin (7.00%, 80.62 μg/g). However, based on a common garden at middle-altitude environment, almost none of the flavonoids was enriched in the high-altitude populations, and even some flavonoids, such as quercetin, tricin, and rutin, were significantly enriched in low-altitude populations. This phenomenon indicated that the accumulation of flavonoids was not a result of local adaptation to high altitude. Furthermore, association analysis with in situ environmental variables showed that the contents of quercetin, tricin, and rutin were strongly positively correlated with latitude, longitude, and precipitation gradients and negatively correlated with temperature gradients. Thus, we could conclude that the accumulations of flavonoids in A. squarrosum were more likely as a result of local adaption to environmental heterogeneity combined with precipitation and temperature other than high altitude. This study not only provides an example to understand the molecular ecological basis of pharmacognosy, but also supplies methodologies for developing a new industrial crop with ecological and agricultural importance.
Highlights
As sessile organisms, plants have evolved to produce a variety of chemical metabolites in the process of adaptation to the changing environment, and each metabolite plays a vital role in responding to abiotic stresses
We proposed that the enrichment of flavonoids in the high-altitude populations of A. squarrosum was a consequence of physiological response to environmental stresses or of genetic differentiation involved in local adaptation to the high altitude
Tricin, and rutin were strongly positively correlated with latitude, longitude, and precipitation gradients, such as annual precipitation (AP), precipitation of the warmest quarter (PWAQ), precipitation of the wettest quarter (PWEQ), and precipitation of the wettest month (PWM)
Summary
Plants have evolved to produce a variety of chemical metabolites in the process of adaptation to the changing environment, and each metabolite plays a vital role in responding to abiotic stresses. The longterm environmental heterogeneity could exert local selection pressure on plants which increases the fitness of individuals in specific environments (Kawecki and Ebert, 2004). When populations inhabit different environments, divergent selection pressure can result in phenotypic differentiation by metabolite accumulation to confer a local fitness advantage (Kawecki and Ebert, 2004). When exhibit better fitness in a local population, metabolites, secondary metabolites, should be variated along with environmental gradients or multiple stresses, such as drought, high and low temperature, UV-B, pathogens, and herbivores (Vanwallendael et al, 2019). It is necessary to elucidate the potential role of secondary metabolites for a plant species to adapt along an environmental gradient
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