UCR

Center for Plant Cell Biology



Zhenbiao Yang


Zhenbiao YangZhenbiao Yang

Professor of Cell Biology

Mailing Address:

Botany and Plant Sciences
Genomics Building /4234B
University of California
Riverside, CA 92521

Phone: (951) 827-7351
Fax: (951) 827-4437
Email: zhenbiao.yang@ucr.edu

Degree(s):

PhD 1990 Virginia Tech
MS 1986 Iowa State University
BS 1982 South China University of Tropical Agricultural

College/Division Affiliation:

College of Natural and Agricultural Sciences

Center/Inst Affiliation(s):

Center for Plant Cell Biology
Center for Research in Intelligent Systems (CRIS)

Areas Of Expertise:

Molecular Cell Biology; G Protein-mediated Signaling Networks and Molecular Mechanisms of Cell Polarity and Cell Morphogenesis in Arabidopsis

Awards / Honors:

2005  AAAS Fellow (American Association for the Advancement of Science)
2005  Japan Society for Promotion of Science Fellow

Research Summary:

The Yang’s laboratory is interested in uncovering the paradigm behind the linkage between signals (e.g., hormones), fundamental cellular processes (e.g., cell polarity formation), and plant development and morphogenesis.   Toward this goal, his group focuses on several inter-linked areas in cell biology: molecular basis for cell polarity and shape formation, hormone signaling, and signaling networks mediated by the Rho family of small GTPase/G protein switches. 

I. GENOME-WIDE STUDIES OF ROP SIGNALING NETWORKS IN ARABIDOPSIS  

The importance of sensing extracellular signals is reflected in the existence of more than 400 plasma membrane (PM) localized receptor-like protein kinases (RLKs) in Arabidopsis, yet how these RLKs are linked to intracellular signaling networks is essentially unknown. Small GTPases are conserved signaling switches (by cycling between the GTP-bound active and GDP-bound inactive forms) responsible for transmitting signals from transmembrane receptors.   The Arabidopsis genome encodes a subfamily of conserved Rho small GTPases, termed ROPs, which act as a “hub” to integrate upstream signals as well as to coordinate downstream pathways (Figure 1). ROP activators, termed guanine nucleotide exchange factors (RopGEFs), are known to interact with RLKs and may integrate various RLK signals. To coordinate various downstream pathways, active ROPs interact with a battery of functionally distinct effector proteins, such as RICs (Rop-interacting CRIB motif-containing proteins), NADPH oxidases, and ICRs. The Yang’s laboratory is carrying out a genome-wide analysis of ROP-mediated signaling networks using genetics, genomics, proteomics, biochemistry, and chemical genetics approaches.

 
Figure 1. A generalized scheme illustrating the role of Rop GTPase as a signaling switch and a “hub” for controlling signaling networks. RLK, receptor-like ser/thr kinases; GEF, guanine nucleotide exchange factor; GDI, guanine nucleotide dissociation inhibitor; RopGAP, Rop GTPase activating protein. RIC, Rop-interacting CRIB-containing proteins. ICR, interactor of constitutively active ROPs.
II. CELL POLARITY AND CELL SHAPE FORMATION

Cell polarity is fundamentally important to plant growth and development. Some well-known examples of polarity in plants include polar cell expansion critical for cell shape formation, polar distribution of auxin carriers in the PM required for directional auxin flow, and asymmetric cell division necessary for cell differentiation.    Unlike single-celled yeast or cultured mammalian cell lines, cell polarity in higher plants is generally developed in multi-cellular context and is not normally expressed in cultured cells. This causes difficulties in studying the molecular basis of cell polarity control in plants, which remained mysterious until recent studies of ROP GTPase signaling. The Yang’s laboratory has used the “single-celled” tip-growing pollen tube as a model to generate hypotheses about the ROP-dependent pathways leading to polar cell expansion and extended these hypotheses to other cell types including planar cell polarity that requires cell-cell coordination in intact tissues.

II.a. The spatiotemporal dynamics of a ROP signaling network controls apical cell polarity and tip growth in pollen tubes.

Pollen tubes provide an ideal model system for the study of apical cell polarity and polar cell growth. In culture, pollen tubes develop a uniform cylindrical shape through an extreme form of polar growth--tip growth, a process involving continuous targeting and fusion of vesicles to a defined region of the PM, termed tip growth domain (Figure 2). The Yang’s laboratory is interested in the mechanisms that define the tip growth domain and control localized vesicle targeting and fusion. His group has shown that the spatiotemporally dynamic, tip-localized ROP1 is at the center of these mechanisms and has developed a model for ROP-dependent control of tip growth (Figure 2). His group is elucidating these using a multi-disciplinary approach that integrates genetics, cell biology, molecular biology, biochemistry, chemical biology, and systems biology.

Figure 2. The pollen tube as a model system for cell polarity studiesA. Cultured pollen tubes show uniform cylindrically-shaped cells. B. Schematics showing polar distribution of the cytoplasm in pollen tubes. Note the apex contains dynamic F-actin and vesicles and the tip growth domain in the PM. C. The localization of GFP-tagged RIC4 indicating the distribution of active ROP1 as a dynamic apical cap in the pollen tube PM, which determines the tip growth domain and controls tip growth. D. A model for spatiotemporal regulation of a ROP signaling network and its role in the control of tip growth. The spatiotemporal dynamics of the apical ROP1 cap is generated by an elaborate mechanism involving interlinking positive and negative feedback loops and controls polarized exocytosis by activating two downstream pathways that check and balance each other. PM-localized ROP1 is locally activated by an unknown cue and its activity is amplified laterally to generate the ROP1 apical cap that determines the tip growth domain. Negative feedback-mediated global inhibition of ROP1 activation limits its lateral amplification, generating the dynamics of the apical ROP1 cap. This dynamics of the apical ROP1 activity controls localized exocytosis through by promoting actin dynamics and cytoslic calcium accumulation at the tip.
II. b. A ROP GTPase signaling network controls planar cell polarity and cell intercalation in the jigsaw-puzzle-shaped pavement cells in the leaf epidermis

Cells within the plane of a tissue usually share a common polarity called planar cell polarity, which is formed through coordination among cells and allows cell-cell coordinate within the tissue. Using Arabidopsis leaf pavement cells of the jigsaw puzzle appearance as a model system, the Yang’s laboratory has an established the framework of a signaling network that underlying the highly coordinate formation of interdigitating lobes and indentations (Figure 3). Interestingly, the central player in this network is also ROP GTPases (ROP2 and ROP4) as in the apical cell polarity and tip growth in pollen tubes, providing some of the first evidence that Rho GTPase-cytoskeleton signaling also control planar cell polarity. Since pavement cell morphogenesis relies on turgor-driven and wall-constrained diffuse growth that is the predominant mechanism for cell expansion in plants, this investigation may ultimately shed light on how cell expansion is controlled by developmental, hormonal, and cell-to-cell signals in developing organs in plants. Current research in the Yang laboratory focuses on identifying the signals that regulate the ROP2/4-dependent network and elucidating this network as well as the inter-cellular signaling mechanisms that coordinate lobe growth with indentation formation.

Figure 3. The development of the jigsaw-puzzle appearance in pavement cells requires a cell-to-cell coordination of intercalary lobe outgrowth and indentation formation. A. Pavement cell morphogenesis involves fine cortical F-actin associated with the tip of lobes and well-ordered cortical microtubules (MTs) associated with the indenting region. B. The jigsaw puzzle appearance of mature pavement cells. C. A model for ROP2 regulation of pavement cell morphogenesis. ROP2 is activated locally by unknown signal(s) and activates RIC4 to promote the assembly of the fine cortical F-actin required for lobe outgrowth. ROP2 also inactivates RIC1, a MT-associated ROP effector protein, which promotes the ordering of cortical MTs in the indenting region. These MTs promotes the indentation as well as suppresses ROP2 activation. The counteraction of the ROP2-RIC4 and RIC1-MT pathways generates the alternating domains of the plasma membrane for lobe and indent formation, respectively. The ROP2 pathway is suspected to produce an extracellular signal that could feedback activates itself for lobe formation and/or regulate the indent formation in the complementary region of the neighboring cell.
III. ROP GTPASES IN PLANT HORMONE SIGNALING 

Although important breakthroughs have been recently made in the understanding of hormone perception in plants, major gaps remain in our understanding of intracellular mechanisms behind hormone signaling, especially those in the PM. Recent work from the Yang laboratory and other groups has implicated PM-localized ROP GTPase signaling in the regulation of several plant hormones. The Yang laboratory has focused on the role of ROPs in ABA (abscisic acid) and auxin signaling. This study takes advantages of ROP knockout mutants combined with a robust novel ROP activity assay developed in this laboratory, which is based on a highly sensitive and quantitative luciferase reporter system. Using these genetic and biochemical assays, the current research is aimed at understanding whether or how individual ROPs and their interacting proteins are connected to known ABA and auxin signaling components or pathways.

Related Press Releases:


List of publications from HubMed
 

Selected Publications:


Yang Lab 2014Lab Personnel:

Harlow, Geoffrey
Graduate Student Researcher
Luo, Nan
Graduate Student Researcher
Zhu, Tiantian
Graduate Student Researcher
Chen, Jisheng
Visiting Researcher/Postdoc
Craddock, Christian
Visiting Researcher/Postdoc
Lavagi, Irene
Visiting Researcher/Postdoc
Li, Hui
Visiting Researcher/Postdoc
Liang, Quixia
Visiting Scientist
Rong, Duoyan
Visiting Student Researcher

Previous Members:

Liu, Gang
Postgraduate Researcher
Nagawa, Shingo
Postgraduate Researcher
Jamin, Augusta
Graduate Student Researcher: Chemical genetics of ROP GTPase signaling in pollen tube growth
Khamsuk, Ornusa
Graduate Student Researcher
Yan, An
Graduate Student Researcher: Roles of receptor-like kinases in pollination
Xu, Tongda
Graduate Student Researcher: Signals and early signaling events that regulate ROP signaling pathways leading to the formation of the jigsaw puzzle appearance in Arabidopsis pavement cells

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Center for Plant Cell Biology
Botany & Plant Sciences Department
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Tel: (951) 827-7177
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E-mail: genomics@ucr.edu

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