Hormonal and transcriptional analyses provides new insights into the molecular mechanisms underlying root thickening and isoflavonoid biosynthesis in Callerya speciosa (Champ. ex Benth.) Schot

Abstract

Callerya speciosa (Champ. ex Benth.) Schot is a traditional Chinese medicine characterized by tuberous roots as the main organ of isoflavonoid accumulation. Root thickening and isoflavonoid accumulation are two major factors for yield and quality of C. speciosa. However, the underlying mechanisms of root thickening and isoflavonoid biosynthesis have not yet been elucidated. Here, integrated morphological, hormonal and transcriptomic analyses of C. speciosa tuberous roots at four different ages (6, 12, 18, 30 months after germination) were performed. The growth cycle of C. speciosa could be divided into three stages: initiation, rapid-thickening and stable-thickening stage, which cued by the activity of vascular cambia. Endogenous changes in phytohormones were associated with developmental changes during root thickening. Jasmonic acid might be linked to the initial development of tuberous roots. Abscisic acid seemed to be essential for tuber maturation, whereas IAA, cis-zeatin and gibberellin 3 were considered essential for rapid thickening of tuberous roots. A total of 4337 differentially expressed genes (DEGs) were identified during root thickening, including 15 DEGs participated in isoflavonoid biosynthesis, and 153 DEGs involved in starch/sucrose metabolism, hormonal signaling, transcriptional regulation and cell wall metabolism. A hypothetical model of genetic regulation associated with root thickening and isoflavonoid biosynthesis in C. speciosa is proposed, which will help in understanding the underlying mechanisms of tuberous root formation and isoflavonoid biosynthesis.

Identification of Isoflavonoid Biosynthesis-Related R2R3-MYB Transcription Factors in Callerya speciosa (Champ. ex Benth.) Schot Using Transcriptome-Based Gene Coexpression Analysis

“…We have previously reported that 15 putative structural genes were involved in isoflavonoid biosynthesis, including HI4 ′ OMT , 2 VRs , 3 CHIs , 2 CHSs , 3 HIDs , 2 IFSs , I3 ′ H , and 4CL [ 10 ]. These genes had different expression patterns among the four different developmental stages (6, 12, 24, and 30 MAG).…”

“…Isoflavonoids are the most important active constituents in C. speciosa [ 25 ]. Isoflavonoids determine the quality of the drugs, and isoflavonoid content varies during the development of tuberous roots [ 10 ]. However, the molecular mechanism of isoflavonoid biosynthesis and accumulation that causes variation in isoflavonoid content remains largely unexplored.…”

“…In potato, StAN1 , a R2R3-MYB activator, previously named StAN2 in some studies, was highly expressed in anthocyanin-pigmented tubers and displayed a positive correlation with the transcript levels of structural genes, as well as with anthocyanin content [ 38 ]. Our previous studies indicated that IFSs , CHSs , HIDs , CHIs , HI4 ′ OMT , and VRs were key isoflavonoid biosynthetic genes [ 10 ]. As expected, the expression patterns showed that most R2R3-CsMYBs in group 3 exhibited similar expression patterns with key isoflavonoid biosynthetic genes.…”

“…15596-018; Invitrogen Life Technologies, Carlsbad, California, USA) as described in the manufacturer's instructions. For each sample, an equal amount (20 μ g) of total RNA (RIN > 8.0) was applied to construct a cDNA library with the method described by Yao et al [ 10 ]. Finally, twelve libraries (three replicates per sample) were sequenced in pair-end (2 × 100 bp) format BGISEQ-500 sequencing platform, reads were processed and de novo assembled, and the results were analyzed by the BGI Tech Solutions Co., Ltd. (BGI Tech) (BGI, Shenzhen, China).…”

“…Recently, the coordinated expression of structural genes in the (iso) flavonoid biosynthetic pathway has been analyzed via the transcriptome data in several legume plant species, such as soybean, Pueraria candollei , and Pueraria lobata [ 6 , 8 , 9 ]. In C. speciosa , we have previously reported that 15 key genes might be involved in the isoflavonoid biosynthesis pathway, including IFSs , CHSs , and VRs [ 10 ].…”