The R2R3-MYB is a large gene family involved in various plant functions, including carotenoid biosynthesis. However, this gene family lacks a comprehensive analysis in wolfberry (Lycium barbarum L.) and other Solanaceae species. The recent sequencing of the wolfberry genome provides an opportunity for investigating the organization and evolutionary characteristics of R2R3-MYB genes in wolfberry and other Solanaceae species. A total of 610 R2R3-MYB genes were identified in five Solanaceae species, including 137 in wolfberry. The LbaR2R3-MYB genes were grouped into 31 subgroups based on phylogenetic analysis, conserved gene structures, and motif composition. Five groups only of Solanaceae R2R3-MYB genes were functionally divergent during evolution. Dispersed and whole duplication events are critical for expanding the R2R3-MYB gene family. There were 287 orthologous gene pairs between wolfberry and the other four selected Solanaceae species. RNA-seq analysis identified the expression level of LbaR2R3-MYB differential gene expression (DEGs) and carotenoid biosynthesis genes (CBGs) in fruit development stages. The highly expressed LbaR2R3-MYB genes are co-expressed with CBGs during fruit development. A quantitative Real-Time (qRT)-PCR verified seven selected candidate genes. Thus, Lba11g0183 and Lba02g01219 are candidate genes regulating carotenoid biosynthesis in wolfberry. This study elucidates the evolution and function of R2R3-MYB genes in wolfberry and the four Solanaceae species.

Machilus microcarpa is a rare national tree species in China and possesses important ornamental and ecological value. M. microcarpa can be planted in low-temperature areas, depending on whether its seedlings can withstand the harm. To face this problem, the annual seedlings of M. microcarpa were subjected to five temperature treatments, and eight physiological indicators were measured. Furthermore, comparative transcriptome analysis was performed between M. microcarpa leaves treated at 25°C and −2.8°C. A total of 9,385 differentially expressed genes (DEGs) were involved in low-temperature stress in M. microcarpa. An upregulated (cobA) and five downregulated (HEM, CHLM, CRD, CLH, and PORA) genes associated with the porphyrin and chlorophyll metabolism pathway may reduce chlorophyll synthesis under low-temperature stress. Upregulation of six DEGs (two GAPDHs, PFK, PGAM, PDC, and PK) involved in the glycolysis/gluconeogenesis pathway provided energy for M. microcarpa under adverse cold conditions. Thirteen upregulated and seven downregulated genes related to antioxidant enzymes were also observed under low-temperature stress. Candidate transcription factors (TFs) played key roles in signal transduction under low-temperature stress in M. microcarpa, and quantitative real-time PCR (qRT-PCR) analysis validated the RNA-seq data. The results provide valuable information for further studies on the cold response mechanisms for low-temperature stress in M. microcarpa.

Wolfberry (Lycium barbarum L.) is an important economic crop widely grown in China. The effects of salt-alkaline stress on metabolites accumulation in the salt-tolerant Ningqi1 wolfberry fruits were evaluated across 12 salt-alkaline stress gradients. The soil pH, Na+, K+, Ca2+, Mg2+, and HCO3− contents decreased at a gradient across the salt-alkaline stress gradients. Based on the widely-targeted metabolomics approach, we identified 457 diverse metabolites, 53% of which were affected by salt-alkaline stress. Remarkably, soil salt-alkaline stress enhanced metabolites accumulation in wolfberry fruits. Amino acids, alkaloids, organic acids, and polyphenols contents increased proportionally across the salt-alkaline stress gradients. In contrast, nucleic acids, lipids, hydroxycinnamoyl derivatives, organic acids and derivatives and vitamins were significantly reduced by high salt-alkaline stress. A total of 13 salt-responsive metabolites represent potential biomarkers for salt-alkaline stress tolerance in wolfberry. Specifically, we found that constant reductions of lipids and chlorogenic acids; up-regulation of abscisic acid and accumulation of polyamines are essential mechanisms for salt-alkaline stress tolerance in Ningqi1. Overall, we provide for the first time some extensive metabolic insights into salt-alkaline stress tolerance and key metabolite biomarkers which may be useful for improving wolfberry tolerance to salt-alkaline stress.

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