Dr. Zongrang Liu 
Research Molecular Biologists     
Zongrang.Liu@ars.usda.gov
Phone: (304) 725-3451 ext. 239 
Fax: (304) 728-2340
Room 434

2217 WILTSHIRE ROAD 
APPALACHIAN FRUIT RS 
KEARNEYSVILLE, WV 25430

Curriculum Vitae

2000- Present

Research Molecular Biologist, USDA-ARS, Appalachian Fruit Research Station, Kearneysville, WV 25430. Duties include conducting research on transgene containment, gene regulation and dormancy and flowering regulation in tree fruits

2009-Present 

Adjunct Faculty. Department of Horticulture, Virginia Polytechnic Institute and State University, Blacksburg VA 24061

1994-2000

Research Associate, Department of Molecular and Cellular Biology, University of Arizona, Tucson, AZ

1992-1994

Postdoc Associate, Department of Biology, Dartmouth College, Hanover, NH

Google Scholar: http://scholar.google.com/citations?user=Qi9P24oAAAAJ&hl=en

Chilling and warm temperature-mediated regulation of floral development, flowering time and dormancy release in fruit trees

Frequent spring frost poses one of the major threats to fruit production, and developing new cultivars with a later flowering trait is highly desirable. Regulation of the flowering time in fruit trees is compounded by the year-long developmental process that is primarily orchestrated by the seasonal thermal conditions. The flower buds in fruit trees, unlike those in annual herbaceous plants that complete initiation, development, and flowering within a single growing season, are initiated in summer and develop in early fall, pause (dormant) in late fall in response to declining temperature or shortening day length, remain dormant in winter, and resume development in early spring. The dormant buds are physiologically unique in that they remain in a dormant state even under optimal growth condition unless they are exposed to chilling temperatures (>0 -<7.5^oC). This chilling requirement is obligatory and directly related to flowering time: the longer chilling required the later flowering. In fact, chilling is not only required for dormancy release but also for floral development programming through critical stages as evidenced by the observation that insufficient chilling permanently arrests floral development, indicating that floral development is tightly coupled with the dormancy release process, and only buds that pass through specific developmental stages are released from the dormant state or become growth-competent.

Warm (or cool) temperatures in early spring also plays a key role in the regulation of the bud development and flowering time as well. The fully chilled floral buds cannot immediately flower but still need to go through a stage of development, and this process is totally dependent on warm temperatures ranging from 10 to 20^oC (cool temperature range) rather than higher ones that are detrimental to gamete development. Similarly, the warm requirement that varies genetically from genotype to genotype, is inversely correlated to flowering time in plants: the longer the warm requirement the later the flowering. It becomes apparent that the temperature regimes at different seasons target distinct stages of floral development, with chilling in winter driving early stages while the warm temperature in early spring driving the later stages of development, which collectively contribute to thermal-mediated regulation of floral development and flowering time in fruit trees.  

Currently, we are taking genomic and epigenetic approaches to analyze genome-wide mRNA, small RNA and epigenetic modifications in peach floral buds treated at different temperature regimes in order to understand how chilling and warm temperatures genetically and epigenetically regulate flowering time, and delineate the thermal one profile and regulatory networks in fruit crops. We are also conducting similar but comparative analyses among peach germplasm with distinct flowering time, and chilling and warming requirements, aiming at pinning down key factors that are involved in perceiving, responding to and translating the seasonal thermal cues into regulatory signals to control the floral bud developmental and flowering programming, and ascertaining how these factors adapt to different geographic climates. The long-term goal of this research is to provide breeders new knowledge, marks, and genes for developing novel cultivars with climate-resilient and spring frost-proof traits in fruit crops.

Elucidation and remediation of genetic and epigenetic misbehaviors of transgene enhancers/promoters in plants

Biotechnology provides plant breeders and researchers unprecedented opportunities for crop improvement especially in fruit trees. It has many advantages over conventional approaches as it can be applied to any crop or species as long as they can be transformed, overcoming genetic barriers between species. It is simple and fast without involving complex genetic linkages and time-consuming breeding processes. The employed gene regulatory elements or enhancers/promoters primarily determine where and when the introduced genes are expressed and function, and play the most critical role in engineering or improving agronomical important traits in plants. Thus, their activity and stability directly impact the stability and performance of the engineered traits. Our recent studies showed that the enhancers/promoters in a transgene state become genetically and epigenetically unstable, with many of them becoming either highly interactive with surrounding regulatory elements or robustly silenced or both, which are further, in some cases, exacerbated by plant developmental programming or environmental stresses. These misbehaviors, if not remedied, inevitably compromise the performance of the engineered traits under field conditions. Given the lack of these misbehaviors in endogenous enhancers/promoters, plant genomes must have evolved specific regulatory apparatus to prevent the enhancers/promoters from engaging in such “illegitimate” activities in vivo. Accordingly, our current research focuses on elucidating the regulatory mechanisms in plants that “discipline” endogenous enhancers’/promoters’ misbehaviors and ensure their functional integrity, as well as developing an entire novel and sound but the currently unavailable technology to reinforce the stability and performance of the employed enhancers/promoters and engineered traits against genetic, epigenetic and environmental interference in transgenic crops.