Research
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Cytoskeleton & Cell Morphogenesis
A complex network of filamentous proteins "the cytoskeleton" is intimately involved in cell division, cell growth and differentiation and sub-cellular, organelle motility. In plants two major cytoskeletal elements are recognized; actin microfilaments and microtubules. The fusion of nucleotide sequences encoding actin-binding or microtubule binding proteins to fluorescent proteins like the Green Fluorescent Protein (GFP) has made it possible to visualize the cytoskeleton, its functioning and regulation in live plant cells.
This section provides a brief glimpse into the pivotal role played by the cytoskeleton in cell shape development in higher plants.
Several reviews have been published on cytoskeletal involvement in plant cell morphogenesis (Kost et al. 1999, Mathur and Huelskamp, 2002, Mathur 2004, Mathur 2006).
General observations from a variety of cytoskeletal-drug treatments and mutant cell studies in different model cell types such as trichomes, root-hairs, hypocotyl-cells suggest the following:
Aberrant microtubule cytoskeleton activity results in a loss of growth directionality. Affected cells tend to grow isotropically and present a generally rounded and swollen appearance.
Aberrant actin cytoskeleton activity results in lower rate of cellular expansion and produces shorter/smaller cells. Alternatively, as seen in Arabidopsis mutants in different subunits of the ARP2/3 complex and its upstream regulators, cells may develop abnormal regions of expansion and non-expansion to produce randomly distorted shapes.
A general model has been proposed. Some interesting parallels suggesting high functional similarity between animal cell forward movement and plant cell extension growth have emerged from our cytoskeletal work (Mathur 2005). Amongst the different actin cytoskeleton regulators that our lab is currently investigating is the putative ARP2/3 complex and its upstream regulators, as well as the actin bundling protein fimbrin.
Live Cell Visualization & Organelle Dynamics
The discovery of the Green Fluorescent Protein (GFP) from Aequorea victoria and creation of different colour variants has revolutionized biology. The plant cell has become fully illuminated! Extrapolation of observations based on static images is rapidly giving way to non-invasive, dynamic, live-cell studies wherein different cellular components and compartments, highlighted through various multicolored targeted fluorescent proteins are studied either independently or in multicolour combinations.
Since 2008 we have created a number of live-imaging probes based on a monomeric green to red photoconvertible Eos fluorescent protein (Schenkel et al. 2008, Mathur et al. 2010, Wozny et al. 2012, Schattat et al. 2012). The mEosFP based probes allow tracking of single organelles, observations on interactions between similar and dis-similar organelles. Our lab uses a large collection of intracellular markers, generated either by us or obtained from other labs, for studying organelle dynamics and interactions in living plant cells. These include marker lines for cell-wall, plasmodesmata, general cytosol, endoplasmic-reticulum, endosomes, filamentous (F)-actin, Golgi-bodies, microtubules, mitochondria, nucleus, peroxisomes, plasma-membrane, pre-vacuolar compartments, and vacuoles.
Some of our recent studies using live-cell probes have involved the actin and microtubule cytoskeleton in leaf epidermal trichomes (Mathur et al. 1999, Mathur and Chua 2002), demonstrated actin dependent intracellular motility of peroxisomes (Mathur et al. 2002), elucidated the role of actin cytoskeleton in organelle distribution and cell morphogenesis (Kirik et al. 2002, Kirik et al. 2002), and visualized plus-end extension and behavior of microtubules (Mathur et al. 2003).Our work has extended to rapid subcellular responses and demonstrated that organelles such as peroxisomes respond to transient increases in ROS stress by extending peroxules (Sinclair et al. 2009, Mathur 2009). Other findings from the lab include the behaviour of plastid extensions called stromules (Schattat et al. 2011, Schattat et al. 2012).
Our lab is presently dissecting the response hierarchy and localized co-operation between plastids, mitochondria and peroxisomes and also between the actin and microtubule components of the cytoskeleton during differential growth in higher plant cells.
Plant Interactions
What is a plant cell's initial reaction to different abiotic and biotic environmental stimuli?
We are using different live-cell probes and a collection of Arabidopsis mutants to document the earliest intracellular responses of plant cells to diverse environmental stimuli. A study by (Sliwinska et al. 2012) shows the co-ordination of endoreduplication and tip-directed nuclear movement during collet hair development in Arabidopsis. Eventually, the data acquired through live imaging and time lapse movies will be compiled into an exhaustive Early Intracellular Response Profiling of Plants (EIRPP). In combination with pertinent molecular-genetic information this would allow us to:
(2), devise specific and innovative strategies for modifying / introducing desirable traits in agronomically important plants.
