Rubber trees are the major source of worldwide natural rubber. Rubber-containing latex is obtained from the laticifer cells of rubber tree (Hevea brasiliensis Muell. Arg.) via regular tapping. However, little is known about the positive feedback regulation of rubber biosynthesis, a typical isoprenoid metabolic process in laticifer cells, by tapping-caused loss of latex. Here, we demonstrated the crucial role of jasmonate signalling in this feedback regulation. The endogenous jasmonate levels, the expression levels of rubber biosynthesis-related genes and the efficiency of in vitro rubber biosynthesis were significantly higher in laticifer cells of regularly tapped trees than those of virgin trees. Application of methyl jasmonate had similar effects to latex exploitation in up-regulating the rubber biosynthesis-related genes and enhancing rubber biosynthesis. The specific jasmonate signalling module (COI1-JAZ3-MYC2) in laticifer cells of rubber tree was further identified. Its activation was associated with the enhanced natural rubber biosynthesis via up-regulating the expression of a farnesyl pyrophosphate synthase gene and a small rubber particle protein gene. The increase in the corresponding proteins, especially the farnesyl pyrophosphate synthase likely contributes to the increased efficiency of rubber biosynthesis. To our knowledge, this is the first study to reveal a jasmonate signalling pathway in regulating rubber biosynthesis in laticifer cells. The identification of the specific jasmonate signalling module in laticifer cells of rubber tree may provide a clue for genetic improvement of rubber yield potential.

Dragon’s blood is a traditional medicine in which flavonoids are the main bioactive compounds; however, the underlying formation mechanism of dragon’s blood remains largely poorly understood. Chalcone isomerase (CHI) is the key enzyme in the flavonoid biosynthesis pathway. However, CHI family genes are not well understood in Dracaena cambodiana Pierre ex Gagnep, an important source plant of dragon’s blood. In this study, 11 CHI family genes were identified from D. cambodiana, and they were classified into three types. Evolutionary and transcriptional profiling analysis revealed that DcCHI1 and DcCHI4 might be involved in flavonoid production. Both DcCHI1 and DcCHI4 displayed low expression levels in stem under normal growth conditions and were induced by methyl jasmonate (MeJA), 6-benzyl aminopurine (6-BA, synthetic cytokinin), ultraviolet-B (UV-B), and wounding. The recombinant proteins DcCHI1 and DcCHI4 were expressed in Escherichia coli and purified by His-Bind resin chromatography. Enzyme activity assay indicated that DcCHI1 catalyzed the formation of naringenin from naringenin chalcone, while DcCHI4 lacked this catalytic activity. Overexpression of DcCHI1 or DcCHI4 enhanced the flavonoid production in D. cambodiana and tobacco. These findings implied that DcCHI1 and DcCHI4 play important roles in flavonoid production. Thus, our study will not only contribute to better understand the function and expression regulation of CHI family genes involved in flavonoid production in D. cambodiana but also lay the foundation for developing the effective inducer of dragon’s blood.

Abscisic acid (ABA) is an essential phytohormone involved in diverse physiological processes. Although genome-wide analyses of the ABA receptor PYR/PYL/RCAR (PYL) protein/gene family have been performed in certain plant species, little is known about the ABA receptor protein/gene family in the rubber tree (Hevea brasiliensis). In this study, we identified 14 ABA receptor PYL proteins/genes (designated HbPYL1 through HbPYL14) in the most recent rubber tree genome. A phylogenetic tree was constructed, which demonstrated that HbPYLs can be divided into three subfamilies that correlate well with the corresponding Arabidopsis subfamilies. Eight HbPYLs are highly expressed in laticifers. Five of the eight genes are simultaneously regulated by ABA, jasmonic acid (JA) and ethylene (ET). The identification and characterization of HbPYLs should enable us to further understand the role of ABA signal in the rubber tree.

Background: Somatic embryogenesis (SE) is a promising technology for plant vegetative propagation, which has an important role in tree breeding. Though rubber tree (Hevea brasiliensisMuell. Arg.) SE has been founded, few late SE-related genes have been identified and the molecular regulation mechanisms of late SE are still not well understood.Results: In this study, the transcriptomes of embryogenic callus (EC), primary embryo (PE), cotyledonary embryo (CE), abnormal embryo (AE), mature cotyledonary embryo (MCE) and withered abnormal embryo (WAE) were analyzed. A total of 887,852,416 clean reads were generated, 85.92% of them were mapped to the rubber tree genome. The de novo assembly generated 36,937 unigenes. The differentially expressed genes (DEGs) were identified in the pairwise comparisons of CE vs. AE and MCE vs. WAE, respectively. The specific common DEGs were mainly involved in the phytohormones signaling pathway, biosynthesis of phenylpropanoid and starch and sucrose metabolism. Among them, hormone signal transduction related genes were significantly enriched, especially the auxin signaling factors (AUX-like1,GH3.1,SAUR32-like,IAA9-like,IAA14-like,IAA27-like,IAA28-likeandARF5-like). The transcription factors includingWRKY40,WRKY70,MYBS3-like,MYB1R1-like,AIL6andbHLH93-likewere characterized as molecular markers for rubber tree late SE.CML13,CML36,CAM-7,SERK1andLEAD-29-likewere also related to rubber tree late SE. In addition, histone modification had crucial roles during rubber tree late SE.Conclusions: This study provides important information to elucidate the molecular regulation during rubber tree late SE.

Dragon’s blood is a red resin mainly extracted from Dracaena plants, and has been widely used as a traditional medicine in East and Southeast Asia. The major components of dragon’s blood are flavonoids. Owing to a lack of Dracaena plants genomic information, the flavonoids biosynthesis and regulation in Dracaena plants remain unknown. In this study, three cDNA libraries were constructed from the stems of D. cambodiana after injecting the inducer. Approximately 266.57 million raw sequencing reads were de novo assembled into 198,204 unigenes, of which 34,873 unique sequences were annotated in public protein databases. Many candidate genes involved in flavonoid accumulation were identified. Differential expression analysis identified 20 genes involved in flavonoid biosynthesis, 27 unigenes involved in flavonoid modification and 68 genes involved in flavonoid transport that were up-regulated in the stems of D. cambodiana after injecting the inducer, consistent with the accumulation of flavonoids. Furthermore, we have revealed the differential expression of transcripts encoding for transcription factors (MYB, bHLH and WD40) involved in flavonoid metabolism. These de novo transcriptome data sets provide insights on pathways and molecular regulation of flavonoid biosynthesis and transport, and improve our understanding of molecular mechanisms of dragon’s blood formation in D. cambodiana.