Principal Investigator, Academician of CAS
Researcher
Email:xychen@sibs.ac.cn
Personal Web: http://sippe.ac.cn/xy

National Key Laboratory of Plant Molecular Genetics

Dr. Xiao-Ya Chen, Professor, CAS Center for Excellence in Molecular Plant Sciences/Institute of Plant Physiology and Ecology, Chinese Academy of Sciences.  

Elected member (Academician) of Chinese Academy of Sciences in 2005 and member of the Academy of Sciences for the Developing World (TWAS) in 2008. 

Education 

1982-1985, Ph.D., Reading University, UK 

1978-1982, B.S., Nanjing University, China 

Working Experience 

1994-Now, Principal Investigator, Professor, Institute of Plant Physiology and Ecology, SIBS, CAS 

1997.5-1997.10, Visiting professor, Nara Institute of Advanced Science and technology, Japan 

1992-1994, Postdoctoral fellow, Purdue University, USA  

1991-1992, Visiting scientist, Tübingen University, Germany 

1989-1991, Associate professor, Nanjing University, China 

1986-1988, Lecturer, Nanjing University, China 

Awards / Honors: 

1. 2017, First Prize of Shanghai Natural Science Award 

2. 2015, Shanghai Science Popular Education Innovation Award 

3. 2014, Outstanding Contribution to Cotton Genomics, the Third ICGI Award 

4. 2008, HLHL Foundation Prize for Scientific and Technological Progress 

Research in my group includes plant specialized metabolism, plant-insect interactions and cotton fiber development. 

Plant specialized or secondary metabolism plays important roles in plant adaptation to environments, particularly in mediating bio-interactions and protecting plants from herbivores and pathogens. Some of the metabolites are highly valuable and used as medicines, food nutrients and in other industrial applications. 

Terpenoids form the largest group of plant secondary metabolites. We are interested in sesquiterpene biosynthesis and regulation. In addition to elucidate the gossypol biosynthetic pathway in cotton (Gossypium spp.) and plant defense against insect herbivores, we also investigate the terpenoid biosynthesis in Arabidopsis and selected medicinal plants, such as Salvia. 

We recently started our project on plant quinones, including in particular the biosynthetic pathway of ubiquinone, or Coenzyme Q (CoQ), in plants and use synthetic biology approaches to crop breeding for better nutrition. 

Cotton fiber, the seed trichome of cotton, is the most important natural fiber for textile industry and a good model to investigate cell elongation and cell wall biosynthesis. In this direction, we are particularly interested in identification of transcription factors and the regulatory complex that control cotton fiber elongation. 

Current projects include: 

(1) Gossypol biosynthesis pathway with emphasis on the novel aromatization mechanisms and distinct modifications; terpenoid biosynthesis in the selected medicinal plants; enzyme evolution and engineering; 

(2) Ubiquinone biosynthesis in plant and improvement of crop nutrition;  

(3) Plant-insect interactions, RNAi technology against insect pests; 

(4) Transcription factors and their complex controlling cotton fiber (trichome) development.  

(1) Elucidation of gossypol biosynthetic pathway and characterization of sesquiterpene synthases  

Gossypol and related sesquiterpenoids in cotton function as defense compounds but are antinutritional in cottonseed products. This group of cotton phytoalexins has a common skeleton of (+)-δ-cadinene. Recent progresses in cotton genomics (Zhang et al., Nature Biotechnology, 2015; Liu et al., Scientific Reports, 2015) have facilitated the gossypol pathway elucidation. By using transcriptome comparison, co-expression analyses and virus-induced gene silencing (VIGS), we identified three P450s (CYP82D113, CYP71BE79 and CYP736A196), a dehydrogenase (DH1) and a dioxygenase (2-ODD-1). These enzymes, together with the previously isolated CYP706B1 (Luo et al., Plant Journal, 2001), decorate the bicyclic (+)-δ-cadinene scaffold for aromatization by a novel mechanism (Tian et al., PNAS, 2018; Tian et al., Phil Trans B, 2019; Huang et al., under review).  

The Artemisia annua amorpha-4,11-diene synthase (AaADS) is a sesquiterpene synthase that catalyzes the first step of artemisinin biosynthesis. Another sesquiterpene synthase, AaBOS, is highly similar to AaADS (sequence identity 92%), but produces a different product: α-bisabolol. Based on the structure of AaBOS, we identified crucial residues for both enzymes. Site-directed mutagenesis has led to a mutant enzyme which holds potential of application in artemisinin production through synthetic biology (Li et al., Biochemical Journal, 2013, Fang et al., Biochemical Journal, 2017).  

(2) Regulation of terpenoids biosynthesis 

The phytohormone jasmonate (JA) is a key regulator of terpenoid biosynthesis in plants. Flowers of many plants, including Arabidopsis, produce and emit a blend of volatile chemicals. In Arabidopsis, we found that both JA and gibberellins (GA) induce sesquiterpene production in flowers. We found that Arabidopsis MYC2, a basic helix-loop-helix (bHLH) transcription factor, directly binds to promoters of the sesquiterpene synthase genes and activate their expression. It also interacts with DELLA proteins to integrate the GA and JA signals to promote sesquiterpene production in flowers (Hong et al., Plant Cell, 2012).  

From Artemisia annua, we isolated two JA-responsive AP2/ERF transcription factors, AaERF1 and AaERF2, which positively regulate artemisinin biosynthesis through binding to the ADS and CYP71AV1 promoters (Yu et al., Molecular Plant, 2012). 

Biosynthesis and accumulation of sesquiterpenes change during plant growth and development. The miR156-targeted SPLs function as a plant age regulator. We found that, in both Arabidopsis and patchouli (Pogostemon cablin, a perennial fragrant plant in the family of Lamiaceae), the miR156-SPL module directly regulates sesquiterpene synthase gene expressions (Yu et al., Molecular Plant, 2015). The age factor also regulates the temporal dynamics of plant resistance to herbivores. We found that the SPL9 can interact with JAZ proteins; as the SPL level elevates with plant age, JAZ accumulates and the JA response attenuates. However, plant defense compounds, such as glucosinolates, accumulate continuously, arming the elder plant with stronger constitutive resistance (Mao et al., Nature Communications, 2017). 

(3) Plant-insect interactions and the RNAi technology for insect control 

We use cotton plant and bollworm as a system to dissect plant-insect interactions. Cotton bollworm (Helicoverpa armigera) has evolved mechanisms that enable them to resist or tolerate to a certain amount of gossypol. We found that a bollworm P450 gene (CYP6AE14) was gossypol-inducible and its expression level correlates with larval growth on gossypol-containing diet. To repress the insect gene, we developed a novel strategy of insect RNAi: plant-mediated insect RNAi. By feeding the larvae with plant tissues expressing the dsRNA targeting CYP6AE14, expression level of this P450 gene in midgut decreased (Mao et al., Nature Biotechnology, 2007). This is one of the pioneering reports of this new generation technology of plant protection. Transgenic cotton plants expressing the double-stranded RNA of CYP6AE14 showed enhanced resistance to cotton bollworms (Mao et al., Transgenic Research, 2011). One of the key steps of food-triggered insect RNAi is the transmission of the RNAi signal to midgut cells. We used plant cysteine proteases to increase PM permeability, simultaneous expression of dsRNA and protease in plant provided better protection against herbivorous insects (Mao et al., Plant Molecular Biology, 2013). 

Further investigation of bollworm P450s revealed that generalists can take advantage of host plant secondary metabolites to elaborate defense systems against other toxic chemicals, impairing this defense pathway by RNAi holds a potential for reducing the required dosages of agrochemicals in pest control (Tao et al., Molecular Ecology, 2012).  

(4) Trichome and cotton fiber development 

Cotton is one of the most important economic crops and cotton fiber, which is the seed-born trichome, is widely used in textile industry. We use the model plant Arabidopsis to dissect the regulation of trichome development and patterning. We found that the miR156-targeted SPLs positively regulate the expression of a trichome repressor (Yu et al., Plant Cell, 2010), and SPL and the miR171-targeted LOM factors function antagonistically to control the trichomes patterning through protein-protein interaction (Xue et al., PLoS Genetics, 2014). 

Cotton fiber is an excellent model for the study of plant cell elongation and cellulose biosynthesis. We have isolated a set of genes involved in fiber cell development, including those encoding MYB, HOX and bHLH transcription factors (Wang et al., Plant Cell, 2004; Guan et al., Physiologia Plantarum, 2008; Shan et al., Nature Communications, 2014; Zhao et al., New Phytologist, 2018), as well as a cell wall protein RDL1 (Li et al., Plant Science, 2002; Xu et al., Molecular Plant, 2012). 

RDL1 interacts with EXPA1, an α-expansin involved in cell wall loosening. Co-expression of RDL1 and EXPA1 in cotton promoted plant growth and fruit production (Xu et al., Molecular Plant,2012). 

We have isolated three homeobox (HOX) transcription factors from cotton, GhHOX1, 2, 3 (Guan et al., Physiologia Plantarum, 2008), among which GhHOX3 functions as a core regulator of cotton fiber elongation. GhHOX3 interacts with GhHD1, another homeodomain-containing protein, resulting in enhanced transcriptional activity. Furthermore, the DELLA protein GhSLR1, repressor of gibberellin (GA), interferes with the GhHOX3-GhHD1 interaction and represses target gene transcription, whereby transducing the GA signal to cotton fiber elongation (Shan et al., Nature Communications, 2014).  

In addition, a HLH transcription factor gene, GhPRE1, is down-regulated following GhHOX3 silencing and it also functions in cotton fiber elongation (Zhao et al., New Phytologist, 2018). These transcription factors prompt us to find more components that work together and form a complex in regulating fiber cell elongation and wall biosynthesis.