Ph.D., Purdue University, 1975
Telephone: (301) 405-1645
Fax: (301) 314-9081
Research Interests: Cell and molecular biology. Understand plant growth, development, adaptation and reproduction through studies of membrane transport.
Membrane transport is essential for almost all cellular processes, and disruption
often results in disease or death. New information, emerging from
the study of completed genomes, has revealed a surprising degree
of conservation of structure of many important membrane transporter
families. Yet we do not know the substrates and mode of action of
most membrane transporters, their regulation, and their impact on
cellular and organ function. Model systems have several advantages.
The genomes have been sequenced, and they can be genetically manipulated,
thus simplifying the study of those transporters that are conserved
among organisms. We are using plants and yeast to identify key transporters
and to understand how organisms sense and respond to changes in
nutrients and toxic compounds in the cell or in the environment.
The essential functions of Ca2+ depend on the spatial and temporal
distribution of this ion within each cell. The dynamic changes of
this ion within the cytosol and internal stores suggest that Ca
channels and pumps are diverse and tightly regulated. Of multiple
Ca-ATPases in Arabidopsis, only a few have been characterized. Major goals are to (1) identify and characterize Ca pumps after
functional expression of plant genes in yeast mutants; (2) understand
how expression and activity of transporters are regulated, and (3)
understand the in vivo functions in plants. T-DNA disrupted mutants
of pumps are being identified, thus allowing us to test for the first time
whether growth, signaling responses, and male fertility are impaired.
Proton pumps occupy a prominent position among all transporters
in plants and yeast. Without the primary motive force to energize
coupled carriers or ion channels, all other transport, and thus
life, would cease. In spite of this, it is not understood how proton
pumps are integrated into the signal transduction networks that
govern growth and adaptation. A major proton pump (vacuolar H+-ATPase)
acidifies the vacuole and endomembrane compartments, and provides
the driving force for transport of many ions and metabolites across
the vacuolar membrane. Many novel H+-coupled cation transporters were uncovered in plant genomes, though their functions are largely unknown. A working model is that H+ pumps and cation/H exchangers affect development, reproduction and tolerance to stress through their effect on endomembrane trafficking.
One goal is to understand these functions at the biochemical
and cellular level using a combination of biochemical,
cellular, molecular, genetic and genomic tools.
(The research programs have been supported by the National Science Foundation, USDA and the Department of Energy.)
Dr. Sze has taught courses in Plant Physiology, Advanced Cell Biology, and a seminar in plant cell
biology. Current courses include
- Plant Physiology- A 4-credit course consisting of 3 h of lecture and 3 h of laboratory taught every fall. Plant Physiology is the study of plant growth, survival and development and the physical, biochemical and molecular mechanisms underlying these processes. The course covers how plants take up inorganic nutrients and water and how nutrients and water are distributed throughout the plant body, how plants convert solar energy to food energy, and how plants respond to environmental and hormonal stimuli in order to develop and to survive.
- Advanced Plant Development and Physiology is a 2 credit course consisting of lectures and journal discussions aimed at graduate students majoring in plant biology. The course takes an integrated experimental approach, including cellular, biochemical, genetic, molecular and functional genomic methods to understand the concepts and principles of major processes, such as plant defense, and plant responses to hormonal and environmental stimuli.
Usually consists of 3-4 members, including postdoctoral fellows and graduate students.
Current members are Dr. Senthilkumar Padmanaban, Yongxian Lu, Salil Chanroj, and Kevin Bock.
Selected Recent Publications:
Liang F, KW Cunningham, JF Harper & H Sze. (1997) ECA1 complements yeast mutants defective in Ca pumps and encodes an ER-type Ca-ATPase in Arabidopsis thaliana. Proc. Natl. Acad. Sci. 94, 8579-8584
Li, X, H-t Hsu, RT Su & H Sze. (1998) The molecular chaperone calnexin associates with the vacuolar H+-ATPase from oat seedling. The Plant Cell 10, 119-130
Hwang, I., F. Liang, JF Harper, and H. Sze (2000). Calmodulin interacts
with the autoinhibitory domain at the N terminus of ACA2, a novel
Ca pump from Arabidopsis. Plant Physiol. 122, 157-167
Sze, H., Xuhang Li, and M. Palmgren. (1999) Energization of the plant cell
membranes by H+-pumping ATPases: biosynthesis and regulation.The
Plant Cell 11,
Hwang I, H. Sze, JF Harper (2000) A Ca-dependent protein kinase
can inhibit a calmodulin stimulated Ca-pump (ACA2) located in the
ER of Arabidopsis . Proc Natl Acad Sci 97, 6224-6229
Sze H, Liang F, Hwang I, Curran A, Harper JF (2000) Diversity and
Regulation of Plant Ca2+ Pumps: Insights from expression in yeast.
Annu Rev Plant Physiol Plant Mol Biol 51: 433-462
Sze H, K Schumacher, ML Muller, S. Padmanaban and Lincoln Taiz.
(2002) A simple nomenclature for a complex proton pump: VHA genes
encode the Vacuolar H+-ATPase. Trends
Plant Sci 7, 157-161
Wu Z, F Liang, B Hong, JC Young, MR Sussman, JF Harper and H Sze
(2002). An ER-bound Ca2+/Mn2+ pump, AtECA1, supports plant growth
and confers tolerance to Mn2+ stress. Plant Physiol. 130:128-37
Padmanaban S, X Lin, I Perera, Y Kawamura and H Sze. (2004) Differential expression of vacuolar H+-ATPase subunit c genes in tissues active in membrane trafficking and their roles in plant growth as revealed by RNAi. Plant Physiol. 134:1514-26
Sze, H, Padmanaban S, Cellier F, Honys D, Cheng NH, KW. Bock, G. Conejero, X Li, Twell D, Ward J, K Hirschi (2004). Expression pattern of a novel gene family, AtCHX, highlights their potential roles in osmotic adjustment and K+ homeostasis in pollen biology. Plant Physiol. 136:2532-47
Bock KW, D Honys, JM. Ward, S Padmanaban, EP Nawrocki, KD Hirschi, D Twell, and H Sze (2006) Integrating Membrane Transport with Male Gametophyte Development and Function through Transcriptomics. Plant Physiol. 140, 1151-1168
Sze H, Frietsch S, Li X, Bock KW, Harper JF (2006) Genomic and Molecular Analyses of Transporters in the Male Gametophyte. In ‘The Pollen Tube’ Ed. R. Malho. Plant Cell Monograph 3, 71 Springer-Verlag.
Padmanaban S, Chanroj S, Kwak J, Li X, Ward JM, Sze H. (2007) Participation of an endomembrane cation/H+ exchanger AtCHX20 in osmoregulation of guard cells. Plant Physiol. 144(1): 82-93