Adaptive Mechanism Exploration of Camellia limonia in Karst High Calcium Environment by Integrative Analysis of Metabolomics and Metagenomics

Camellia limonia is a kind of rare plant with high economic and medicinal value. It’s a plant species growing in calcareous soil of limestone, which means they can grow well in high calcium environment. Compared with C. limonia, Camellia nitidissima is a plant growing in acidic soil, which grows slowly or even dies in high calcium environment. However, there are few studies on C. limonia in karst soil environment and its adaptation mechanism is no clear. In this study, we found that under high calcium treatment, the chlorophyll content and leaf areas of C. limonia increased, while those of C. nitidissima decreased. The photosynthetic efficiency of C. limonia was more stable and higher than C. nitidissima. Compared with C. nitidissima, the conductance was larger and the degree of leaf shrinkage was smaller in C. limonia. The metabolomics analysis of both leaves showed that the kaempferol-3-o-rutinoside, tyrosol, 6-o-methyldeacetylisoipecoside and (r)-mandelic acid are the main differently metabolic compounds. The results of metagenomics in karst soil showed that the secretion (propylene oxide) of Acaryochloris marina in rhizosphere is closely related to the adaptation of C. nitidissima in high-calcium regions. Through metabolomics and metageomics integrative analysis, flavone and flavonol biosynthesis were suggested to be the main regulation pathway, which were regulated by metabolites apigenin, kaempferol, astragalin, isoquercitrin and genes TT7, UGT78D1, UGT78D2. This metabolic pathway involved the synthesis of flavonoids. Flavonoids have the characteristics of drought resistance and salt resistance, which play an important role in the adaptation of C. limonia in karst high calcium environment. This omics study identified key regulation metabolites and genes for Camellia and provided important basis for the adaptive mechanism of plants to adapt to the high-calcium environment and the protection of Camellia species.