School of Biological Sciences

The University of Hong Kong

Professor M. L. Chye
Wilson and Amelia Wong Professor in Plant Biotechnology

MLC

Tel. +852 2299-0319

M.L. Chye completed her PhD on a Commonwealth Scholarship at the University of Melbourne and received postdoctoral training in Plant Molecular Biology at the Rockefeller University (New York) and the Institute of Molecular and Cell Biology (Singapore). She joined the University of Hong Kong as a Lecturer in 1993 and was promoted to Professor in 2005. She has been awarded an Edward Clarence Dyason Universitas 21 Fellowship 2004/05, an Outstanding University Researcher Award 2006/07 and a Croucher Senior Research Fellowship 2007/08. She serves on the editorial boards of Planta (Springer), Frontiers in Plant Metabolism & Chemodiversity and Frontiers in Plant Physiology, and was Chair of the Asian Symposium on Plant Lipids 2011 (http://www.biosch.hku.hk/aspl2011) .

Laboratory of Plant Molecular Biology

Research Team

 

Research Interests

The main focus of the Chye Lab is to understand the function and mechanism of action of stress-induced plant proteins, particularly plant acyl-CoA-binding proteins (ACBPs). We intend to use them to generate transformed plants that can better tolerate abiotic and biotic stresses since these stresses account for ~40 % loss in crop productivity. Ultimately, investigations on plant ACBPs, and others, will be applied to agriculture and phytoremediation. Our projects have been supported by the Research Grants Council of Hong Kong and the Plant and Agricultural Biotechnology Area of Excellence, University Grants Committee (http://www.cuhk.edu.hk/bio/aoe/). Collaboration with fellow members of the State Key Lab of Agrobiotechnology, Chinese University of Hong Kong (http://www.cuhk.edu.hk/ipmbab/SKL/index.html), will enable us to extend our findings on the model plant, Arabidopsis thaliana, to rice which is an important staple crop in China.

Arabidopsis acyl-CoA-binding proteins (ACBPs) and stress tolerance

We are studying a family of plant ACBPs which bind acyl-CoA esters and transport them within the plant cell. In the model plant Arabidopsis, six genes encode four structurally distinct classes of ACBPs (Leung et al., 2004; Xiao and Chye, 2009):

  1. 10-kDa cytosolic ACBP of which homologues have been well-characterized in other eukaryotes (Chen et al., 2008),
  2. membrane-associated ACBPs with ankyrin repeats, ACBP1 and ACBP2 (Chye et al., 1999; Li and Chye, 2003; 2004; Xiao et al., 2008a; Chen et al., 2010; Du et al., 2010; Gao et al., 2009; 2010),
  3. ACBP3 (Leung et al., 2006; Xiao et al., 2010) and
  4. cytosolic kelch-motif containing ACBP4 and ACBP5 (Leung et al., 2004; Li et al., 2008; Xiao et al., 2008b; 2009).

In our attempt to understand the function of Arabidopsis ACBPs, we have identified the amino acid residues in the acyl-CoA-binding domain that are important in binding acyl-CoA esters (Chye et al., 2000; Leung et al., 2004; 2006). Some ACBPs can also bind phospholipids (Chen et al., 2008; Du et al., 2010; Chen et al., 2010; Xiao et al., 2010). On lipid analysis, Arabidopsis acbp mutants and transgenic Arabidopsis lines overexpressing ACBPs showed alterations in lipid composition (Xiao et al., 2008b; 2010; Chen et al., 2008; 2010; Du et al., 2010). ACBPs with ankyrin repeats (Li and Chye, 2004; Gao et al., 2009; 2010) and kelch motifs (Leung et al., 2004; Li et al., 2008; Xiao et al., 2008b) have been demonstrated to mediate protein-protein interactions.

We have observed that certain ACBPs are induced by various forms of abiotic and biotic stresses (Xiao et al., 2008a; Li et al., 2008; Chen et al., 2008; Gao et al., 2009; 2010). Subsequently, when these ACBPs were overexpressed in transgenic plants, the resultant lines were conferred stress tolerance. ACBP6-overexpressors are freezing tolerant (Chen et al., 2008) while ACBP1- and ACBP2-overexpressors are tolerant to heavy metal and oxidative stresses (Xiao et al., 2008; Gao et al., 2009; 2010). Interestingly, ACBP1-overexpressors accumulate Pb(II) in shoots making ACBP1 applicable for phytoremediation, a low-cost solar-driven process that removes pollutants from the environment in situ (Xiao et al., 2008a, Xiao and Chye, 2008; US Patent No. 7,880,053).

please click photos to enlarge

Stress-inducible HMGS, an enzyme in plant isoprenoid metabolism

We are investigating the role of 3-hydroxy-3-methylglutaryl-CoA synthase (HMGS) in plant isoprenoid metabolism. HMGS is an enzyme in the cytosolic mevalonate pathway which produces sterols, sesquiterpenes and polyterpenes. Its expression is stress-inducible and is highest during early development in flower, seed and seedling (Alex et al., 1999). Four isogenes encoding HMGS are differentially expressed in Brassica juncea (Nagegowda et al., 2005). Using green fluorescent protein fusions, B. juncea HMGS1 (BjHMGS) has been subcellularly localized to the cytosol (Nagegowda et al., 2005). We have biochemically purified and characterized His-tagged recombinant BjHMGS expressed in Escherichia coli, presenting a first detailed characterization of a plant HMGS, and the amino acids involved in catalysis were identified by site-directed mutagenesis (Nagegowda et al., 2004). In collaboration with the Bach Lab and the Noel Lab, the crystal structure of Brassica HMGS covalently bound to specific inhibitor F-244 has been determined, providing a first approach towards the design of more potent cholesterol-lowering drugs and antibiotics that target the mevalonate pathway (Pojer et al., 2006).

Expression of siRNAs and heterologous proteins in genetically-transformed plants

Some of the strategies currently used to engineer crops to stress tolerance exploit the natural mechanisms used by the plant. We have isolated defense-related genes from tropical plants for expression in transgenic crops. To this end, we have cloned and characterized cDNAs encoding beta-1, 3-glucanase from Hevea brasiliensis (Chye and Cheung, 1995, Plant Mol Biol 29: 347-402) and an unusual Brassica juncea chitinase with two chitin-binding domains, designated BjCHI1 (Zhao and Chye, 1999; Fung et al., 2002). Potato transgenic for both proteins was protected from Rhizoctonia solani invasion (Chye et al., 2005). Besides displaying anti-fungal properties, BjCHI1 with its two chitin-binding domains can agglutinate Gram-negative bacteria (Tang et al., 2004; Guan et al., 2008). BjCHI1-susceptible fungal and bacterial phytopathogens have been identified for future applications in agriculture (Guan et al., 2008; Guan and Chye, 2008; US Patent No. 6,956,147). To better understand the function of plant chitinases in catalysis, we have examined their crystal structures with the Mowbray Lab (Ubhayasekara et al., 2007; 2009).

Research on proteinase inhibitor protein SaPIN2a from a weed, Solanum americanum (Xu et al., 2001), has not only led to the production of transgenic lettuce that are insect-resistant but that also show inhibition of endogenous trypsin- and chymotrysin-like activities (Xu et al., 2004). Thus, SaPIN2a can be used to protect heterologously expressed proteins by minimizing protein degradation and optimizing protein yield in transgenic plant bioreactors (US Patent No. 7,256,327). SaPIN2a and SaPIN2b function endogenously by inhibiting proteinase activities in phloem and floral development (Xu et al., 2001; Sin and Chye, 2004). We have used RNAi-based gene silencing to show that SaPIN2a and SaPIN2b are essential for seed development (Sin et al., 2006). A reduction in seed set was observed in PIN2-RNAi transgenic S. americanum lines; aborted seeds in transgenic fruits had an abnormal endothelium, suggesting that the endothelium allows proper endosperm and embryo formation through its ability to produce a proteinase inhibitor (Sin et al., 2006).

In other projects related to plant biotechnology, we have explored the use of transgenic plants as bioreactors for the production of vaccines using nuclear transformation and plastid transformation (Zhou et al., 2006; Lee et al., 2006; Li et al., 2006; Li and Chye, 2009; Chye et al., Chinese Patent No. zl200480039355.6).

Representative Publications

 

Last modified: 7/12/2011

Please send suggestions and comments to mlchye@hku.hk.