During the evolution, plants acquired the ability to synthesize different phenylpropanoid compounds like chlorogenic acid (CGA), which plays vital roles in resistance mechanisms to abiotic stresses. These environmental factors, including heavy metal, cold, heat, ultraviolet (UV) light, drought, and salinity affect the plant physiological processes, resulting in massive losses of agriculture production. As plants evolve from green algae to bryophytes, ferns, gymnosperms and angiosperms, phenylpropanoids are produced and accumulated in different tissues, giving the plant the capacity to counteract the harmful effects of the adverse environments. Studies have been performed on the metabolic evolution of rosmarinic acid, flavonoids and lignin, showing that the biosynthesis of phenylpropanoids begins in green algae until the emersion of genes found in angiosperms; however, the evolution of the CGA pathway has not yet been reviewed. We hypothesize that CGA could also be synthesized from algae to angiosperms. In the present review, the evolutionary analysis of CGA pathway and the function of this compound in plant tolerance to abiotic stresses are summarized. Bioinformatics analyzes were carried out on CGA-related genes across 37 plant species and revealed that the metabolic pathway starts in algae and gradually increases until it becomes complete in angiosperms. The key genes exhibited different expression patterns in stress and plant tissues. Interestingly, some genes accumulated rapidly during evolution and were more sensitive to environmental stresses, while others appeared only later in angiosperms. Further studies are needed to better understand the evolution of the CGA metabolic pathway in plants under environmentally stressed conditions.

Glutathione S-transferases (GSTs) are proteins synthesized in plants and responsible for their tolerance to environmental stresses. However, little information is available on the GST gene family of sweet potato, a globally important crop. The genetic evolution of GSTs in sweet potato remains unclear. The present study investigated the GST gene family in sweet potato by transcriptomic and comparative genomic analyses. A total of 51 GSTs were identified. Gene expression analysis showed differential expression patterns of the GSTs between two investigated varieties. Some GST expression levels were either up-or downregulated under oxidative, salinity and drought stresses. The results of the investigation provided new insights on the GST gene family in sweet potato, which may further the understanding of the roles of these genes in regulating abiotic stresses.

Leafy sweet potato is rich in caffeoylquinic acids (CQAs), including monoCQAs and diCQAs, which are important for plant resistance to environmental stresses. Knowledge about genes responsible for the accumulation of these CQAs is limited. However, the implication of glutathione S-transferase (GST) genes in the metabolism of plant secondary compounds has been reported. Yet, the mechanism of CQA-related GST proteins is not well understood. In this study, two sweet potato GST genes i.e., itb01g35330 (IbGSTTCHQD) and itb09g30700 (IbGSTT) were selected from our transcriptome database as they exhibited secondary metabolism functions based on gene ontology classification, and investigated for their association with the accumulation of CQAs. Sequence comparison of the IbGST coding regions amplified from EC16 and FS7-6 leafy sweetpotato varieties revealed some mutations at different sites in the amino acid sequences between the two varieties. Besides, the genes were highly expressed in EC16 compared to FS7-6, which corresponded to the amounts of CQAs in both varieties. The amplified sequences from EC16 were further transformed into Agrobacterium tumefaciens and subsequently introduced into Nicotiana benthamiana and Nicotiana tabacum for transient expression and transgenic transformation, respectively. Gene expression profiling in both experimental methods revealed significant increases of IbGST transcripts in transformed leaves, resulting in enhanced amount of monoCQAs compared to the wild types. However, no significant change was observed in the level of diCQAs. Moreover, the IbGSTs responded positively to salinity and oxidative stresses. Our findings suggested that IbGSTTCHQD and IbGSTT genes might be involved in the accumulation of monoCQAs in leafy sweet potato.

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