Comparative Proteomic Analysis Reveals the Molecular Mechanisms Underlying the Accumulation Difference of Bioactive Constituents in Glycyrrhiza uralensis Fisch under Salt Stress

Licorice
(Glycyrrhiza uralensis Fisch)
possesses a substantial share of the global markets for its unique
sweet flavor and diverse pharmacological compounds. Cultivated licorice
is widely distributed in northwest regions of China, covered with
land with a broad range of salinities. A preliminary study indicated
that suitable salt stress significantly increased the content of bioactive
constituents in licorice. However, the molecular mechanisms underlying
the influence of salinity on the accumulation of these constituents
remain unclear, which hinders quality breeding of cultivated licorice.
In our study, flavonoid-related structural genes were obtained, and
most of them, such as phenylalanine ammonia-lyases, cinnamate 4-hydroxylases,
4-coumarate: CoA ligases, chalcone synthases, chalcone–flavanone
isomerase, and flavonol synthase, showed high levels after salt treatment.
In the biosynthesis of glycyrrhizin, three key enzymes (bAS, CYP88D6,
and CYP72A154) were identified as differentially expressed proteins
and remarkably upregulated in the salt-stressed group. Combining these
results with the contents of 14 bioactive constituents, we also found
that the expression patterns of those structural proteins were logically
consistent with changes in bioactive constituent profiles. Thus, we
believe that suitable salt stress increased the accumulation of bioactive
constituents in licorice by upregulating proteins involved in the
related biosynthesis pathways. This work provided valuable proteomic
information for unraveling the molecular mechanism of flavonoid and
glycyrrhizin metabolism and offered fundamental resources for quality
breeding in licorice.