ABSTRACT
BACKGROUND: Unfavorable temperatures significantly constrain the quality formation of Dendrobium officinale, severely limiting its food demand. Salicylic acid (SA) enhances the resistance of D. officinale to stress and possesses various analogs. The impact and mechanism of the SA family on improving the quality of D. officinale under adverse temperature conditions remains unclear. RESULTS: Combined with molecular docking analysis, chlorophyll fluorescence and metabolic analysis after treatments with SA analogues or extreme temperatures are performed in this study. The results demonstrate that both heat and cold treatments impede several main parameters of chlorophyll fluorescence of D. officinale, including the ΦPSII parameter, a sensitive growth indicator. However, this inhibition is mitigated by SA or its chemically similar compounds. Comprehensive branch imaging of ΦPSII values revealed position-dependent improvement of tolerance. Molecular docking analysis using a crystal structure model of NPR4 protein reveals that the therapeutic effects of SA analogs are determined by their binding energy and the contact of certain residues. Metabolome analysis identifies 17 compounds are considered participating in the temperature-related SA signaling pathway. Moreover, several natural SA analogs such as 2-hydroxycinnamic acid, benzamide, 2-(formylamino) benzoic acid and 3-o-methylgallic acid, are further found to have high binding ability to NPR4 protein and probably enhance the tolerance of D. officinale against unfavorable temperatures through flavone and guanosine monophosphate degradation pathways. CONCLUSIONS: These results reveal that the SA family with a high binding capability of NPR4 could improve the tolerance of D. officinale upon extreme temperature challenges. This study also highlights the collaborative role of SA-related natural compounds present in D. officinale in the mechanism of temperature resistance and offers a potential way to develop protective agents for the cultivation of D. officinale.
Subject(s)
Dendrobium , Molecular Docking Simulation , Salicylic Acid , Dendrobium/metabolism , Dendrobium/drug effects , Salicylic Acid/metabolism , Salicylic Acid/pharmacology , Metabolic Networks and Pathways/drug effects , Plant Proteins/metabolism , Temperature , Chlorophyll/metabolismABSTRACT
The occurrence of betalains and anthocyanins is mutually exclusive, which is a curious phenomenon in the plant kingdom, and the biochemical mechanisms for this restriction are unknown. In the present study, we performed transcriptome analysis of two betalain-producing species, red Bougainvillea glabra Choisy. 'Sanderiana' (R) and white B. glabra 'Alba' (W) by transcriptome sequencing. In total, we obtained 69692 (Red) and 60727 (White) genes with an average length of 665 and 728bp respectively. Out of 3106 significantly differentially-expressed genes (71%), 1003 were R-specific (32%), and 1605 were W-specific (52%). To validate betalain-/anthocyanidin-biosynthesis genes detected (cytochrome P 450 76AD1 (CYP76AD1), dihydroxy-phenylalanine (DOPA)-4,5-dioxygenase (DODA), cyclo DOPA-5-O-glycosyltransferase (cyclo-DOPA-5-GT) dihydroflavonol 4-reductase (DFR), leucoanthocyanidin dioxygenase (LDOX)), real-time PCR was performed in leaves and three development stages of flowers in four Bougainvilleas, red R, white W, orange Bougainvillea×buttiana 'Salmoea' (O) and purple B. glabra 'Formosa' (P). Contents of betalains were also measured. The results showed that betalains accumulation was consistent with the expression level of DODA in O. A correlation between expression of CYP76AD1 and cyclo-DOPA-5GT and betalains was not discovered. This suggests that production of betacyanins was under the regulation of more complex factors. Both DFR and LDOX responsible for anthocyanidin production were first validated in floral organs and leaves in betalain-producing plants by real-time PCR. These findings suggest a fully functioning anthocyanin pathway, at least, to the stage of LDOX in bougainvilleas.