Transcriptome and Metabolic Profiling Provides Insigh into Betalain Biosynthesis and Evolution in Mirabilis jalapa

Betalains are tyrosine-derived pigments that occur solely in one plant order, the Caryophyllales, where they largely replace the anthocyanins in a mutually exclusive manner. In this study, we conducted multi-species transcriptome and metabolic profiling in Mirabilisjalapa and additional betalain-producing species to identify candidate genes possibly involved in betalain biosynthesis. Among the candidates identified, betalainrelated ytochrome P450 and glucosyltransferase-type genes, which catalyze tyrosine hydroxylation or （hydroxy）cinnamoyl-glucose formation, respectively, were further functionally characterized. We detected the expression of genes in the flavonoid/anthocyanin biosynthetic pathways as well as their metabolite intermediates in betalain-accumulating M. jalapa flowers, and found that the anthocyanin-related gene ANTHOCYANIDIN SYNTHASE （MjANS） is highly expressed in the betalain-accumulating petals. However, it appears that MjANS contains a significant deletion in a region spanning the corresponding enzyme active site. These findings provide novel insights into betalain biosynthesis and a possible explanation for how anthocyanins have been lost in this plant species. Our study also implies a complex, non-uniform history for the loss of anthocyanin production across betalain producers, previously assumed to be strictly due to diminished expression of anthocyanin-related genes.

Getting to the bottom of Taxol biosynthesis by fungi

t Taxol(paclitaxel)is a highly-oxygenated diterpenoid natural product first isolated from the pacific yew tree(Taxus brevifolia).It is one of the most widely used anticancer drugs.Soon after the discovery of its unique mode of action and the resulting high demand,an extensive search was initiated for alternative sources to replace the slow-growing and scarce pacific yew.Thus far,however,Taxol and related compounds have only been found in the genus Taxus,which comprises a small number of slow-growing plants with a broad but generally isolated geographical distribution.In 1993,Stierle and colleagues reported the independent biosynthesis of Taxol in an endophytic fungus isolated from Taxus brevifolia,which resulted in more than 160 subsequent publications and patents addressing the biosynthesis of Taxol and related taxanes by microorganisms.The literature on fungal taxane synthesis contains numerous inconsistencies,prompting us to thoroughly re-examine Taxol biosynthesis in endophytic fungi associated with Taxus spp.Using a combination of phytochemistry,molecular biology and genome sequencing,we were unable to find any evidence for independent taxane biosynthesis in any of the endophytes,including the isolate described in the original publication(Taxomyces andreanae)and several more recent isolates from Taxus trees.Our findings therefore resolve a long-standing mystery concerning the evolution of a complex terpenoid biosynthetic pathway in two distantly-related organisms.

The biosynthetic pathway of the hallucinogen mescaline and its heterologous reconstruction

Mescaline,among the earliest identified natural hallucinogens,holds great potential in psychotherapy treatment.Nonetheless,despite the existence of a postulated biosynthetic pathway for more than half a century,the specific enzymes involved in this process are yet to be identified.In this study,we investigated the cactus Lophophora williamsii(Peyote),the largest known natural producer of the phenethylamine mescaline.We employed a multi-faceted approach,combining de novo whole-genome and transcriptome sequencing with comprehensive chemical profiling,enzymatic assays,molecular modeling,and pathway engineering for pathway elucidation.We identified four groups of enzymes responsible for the six catalytic steps in the mescaline biosynthetic pathway,and an N-methyltransferase enzyme that N-methylates all phenethylamine intermediates,likely modulating mescaline levels in Peyote.Finally,we reconstructed the mescaline biosynthetic pathway in both Nicotiana benthamiana plants and yeast cells,providing novel insights into several challenges hindering complete heterologous mescaline production.Taken together,our study opens up avenues for exploration of sustainable production approaches and responsible utilization of mescaline,safeguarding this valuable natural resource for future generations.