Zanthoxylum bungeanum Maxim. leaves (ZBLs) are rich in flavonoids and have become popular in nutrition, foods and medicine. However, the flavonoid components in ZBLs and the mechanism of flavonoid biosynthesis under drought stress have received little attention. Here, we performed an integrative analysis of the metabolome and transcriptome of ZBLs from HJ (Z. bungeanum cv. “Hanjiao”) and FJ (Z. bungeanum cv. “Fengjiao”) at four drought stages. A total of 231 individual flavonoids divided into nine classes were identified and flavones and flavonols were considered the most abundant flavonoid components in ZBLs. The total flavonoid content of ZBLs was higher in FJ; it increased in FJ under drought stress but decreased in HJ. Nine-quadrant analysis identified five and eight differentially abundant flavonoids in FJ and HJ leaves, respectively, under drought stress. Weighted gene correlation network analysis (WGCNA) identified nine structural genes and eight transcription factor genes involved in the regulation of flavonoid biosynthesis. Moreover, qRT-PCR results verified the accuracy of the transcriptome data and the reliability of the candidate genes. Taken together, our results reveal the flavonoid components of ZBLs and document changes in flavonoid metabolism under drought stress, providing valuable information for nutrition value and food utilization of ZBLs.
As an important economical plant, Zanthoxylum bungeanum is widely cultivated in arid and semi-arid areas. The studies associated with photosynthesis under drought stress were widely carried out, but not yet in Z. bungeanum. Here, the photosynthesis of two Z. bungeanum cultivars (FJ, Z. bungeanum cv. “Fengjiao”; HJ, Z. bungeanum cv. “Hanjiao”) was analyzed under drought stress using physiological indicators and transcriptome data. Drought decreased stomatal aperture and stomatal conductance (Gsw), reduced transpiration rate (E) and sub-stomatal CO2 concentration (Ci), and lowered chlorophyll and carotenoid content, which reduced the net photosynthetic rate (Pn) of Z. bungeanum. The higher photosynthetic rate in HJ stemmed from its higher chlorophyll content, larger stomatal aperture and Gsw, and higher Ci. Weighted gene co-expression network analysis (WGCNA) identified several ABA signal transduction genes (PYL4, PYL9, and PYR1), LCH-encoding genes (LHCB4.3), and chlorophyll metabolism genes (CRD1, PORA, and CHLH). Additionally, seven transcription factor genes were identified as important factors regulating photosynthesis under drought conditions. In general, a photosynthetic response model under drought stress was built firstly in Z. bungeanum, and the key genes involved in photosynthesis under drought stress were identified. Therefore, the results in our research provide important information for photosynthesis under drought and provided key clues for future molecular breeding in Z. bungeanum.
NAC (NAM, ATAF1/2, and CUC2) transcription factors (TFs) are one of the largest plant-specific TF families and play a pivotal role in adaptation to abiotic stresses. The genome-wide analysis of NAC TFs is still absent in Zanthoxylum bungeanum. Here, 109 ZbNAC proteins were identified from the Z. bungeanum genome and were classified into four groups with Arabidopsis NAC proteins. The 109 ZbNAC genes were unevenly distributed on 46 chromosomes and included 4 tandem duplication events and 17 segmental duplication events. Synteny analysis of six species pairs revealed the closely phylogenetic relationship between Z. bungeanum and C. sinensis. Twenty-four types of cis-elements were identified in the ZbNAC promoters and were classified into three types: abiotic stress, plant growth and development, and response to phytohormones. Co-expression network analysis of the ZbNACs revealed 10 hub genes, and their expression levels were validated by real-time quantitative polymerase chain reaction (qRT-PCR). Finally, ZbNAC007, ZbNAC018, ZbNAC047, ZbNAC072, and ZbNAC079 were considered the pivotal NAC genes for drought tolerance in Z. bungeanum. This study represented the first genome-wide analysis of the NAC family in Z. bungeanum, improving our understanding of NAC proteins and providing useful information for molecular breeding of Z. bungeanum.
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