Ph.D. Biology Harvard University, 1975
B.S. Botany University of California, Davis, 1967
The Feldman Lab researches plant development e.g. how the populations of cells in and around the meristem interact to control root development. We've shown that quiescent center formation precedes organization of a root meristem, and that high levels of enzyme ascorbic acid oxidase occur within the quiescent center. We use microarrays to characterize quiescent center expression profiles, and to study the many original and unique differentiation events occurring in the root cap as it perceives and transduces environmental stimuli.
Our lab's interests are in the area of plant development, with an emphasis on meristems, particularly those of roots. We are investigating how the various populations of cells which comprise or surround the meristem interact to control root development, especially patterning. Much of our recent effort has focused on two populations of cells: the root cap, and a region of mitotically inactive cells known as the quiescent center. We have shown that quiescent center formation precedes the organization of a root meristem and have hypothesized that a quiescent center is necessary for meristem organization. Based on characteristics of cells comprising the quiescent center we believe that these cells are true “stem cells” in the animal sense. Much of our current work is directed at understanding the underlying molecular and physiological controls of this “stemness”.
Recently, we have shown that the quiescent center maintains a relatively oxidizing (redox) microenvironment and that this is accompanied by low levels in the quiescent center of the two major redox regulators in organisms, gluthathione and ascorbic acid. By altering the redox status, making it relatively more reducing, we are able to stimulate cells in the quiescent center to divide and to lose their stem cell characteristics.
We have hypothesized that the local accumulation of auxin at the embryo pole is THE formative event in the establishment of a quiescent center (a stem cell niche), around which the root meristem organizes. Linking auxin accumulation and meristem establishment is currently a major focus in the lab. We believe that an important intermediate step in meristem establishment is an auxin-induced change in redox status in the presumptive quiescent center. In order to monitor hypothesized auxin-induced changes in redox status we have developed a GFP which when irradiated with two different wavelengths of light provides a ratiometric measurement of redox status in specific regions/cells in the root (Plant Physiology 141: 397-403). Using this new tool we will probe further events associated with auxin-induced root meristem establishment.
We also have evidence that changes in mitochondria physiology are associated with the formation of the quiescent center. Using GFP markers specific to the quiescent center, and by using microarrays, we are examining molecular events underlying quiescent center (and root mersitem) formation. These efforts depend on the use of a new technique known as laser capture microdissection which allows us to use a laser to dissect our specific cells which can be further examined and characterized by RT-PCR. The background for much of this work is explained in a recent review [Jiang, K. and Feldman, L.J. (2005) Regulation of Root Apical Meristem Development. Annu Rev Cell Dev Biol. 2005 Vol. 21: 485-509 pdf 540 kb].
Radish seedling. Arrow points to root cap.
We also are investigating the root cap, which is the terminal-most population of cells in a root. The root cap is the site of perception for many environmental stimuli, including gravity and light. Hence, it has much of its physiology and biochemistry devoted to the perception and transduction of environmental stimuli. We investigate how the cap communicates with the rest of the root. The cap also represents a unique population of cells which, in a space of 0.5 mm, initiates, differentiates, and then releases cells to the external environment where these detached cells may continue to live for up to 7 days. Using microarrays, we are studying the many original and unique differentiation events occurring in the cap and have examined many unique activities in the cap including it ability to sense many environmental stresses and stimuli, including gravity. This work has been recently described in, Transcription Profile Analyses Identify Genes and Pathways Central to Root Cap Functions in Maize (2005) Keni Jiang, Shibo Zhang, Stanley Lee George Tsai, Kyungpil Kim, Haiyan Huang Tong Zhu and Lewis J. Feldman. Plant Molecular Biology 60: 343-360.
Shown below are (a) RAMs of Arabidopsis thaliana and (b,c) Zea mays showing the location of various cell populations. For b and c, note the convergence of cell files to a small number of cells, circumscribed in blue-green (the originally designated promeristem). QC, quiescent center; PM, proximal meristem; RC, root cap; RCI, root cap initials; RCJ, root cap junction. Scale bar = 100 m.
With regard to graduate student research, I encourage graduate students to select and develop their own research projects. This increases the diversity of projects being done in the lab and makes for a broader graduate research experience. Graduate student projects have included: studies of the transition to flowering in Arabidopsis; physiology and development of the peanut gynophore; the genetic and molecular basis for leaf shape in Arabidopsis. Current graduate student research involves characterizing the role of the cle family of genes in Arabidopsis root development.
Jiang, K. and Feldman, L.J. (2005) Regulation of Root Apical Meristem Development. Annu Rev Cell Dev Biol. 2005 Vol. 21: 485-509 pdf 540 kb
Jiang, K, Zhang, S, Lee, S, Tsai, G, Kim, K, Huang, H, Zhu, T, and Lewis J. Feldman, L.J. (2005) Transcription Profile Analyses Identify Genes and Pathways Central to Root Cap Functions in Maize. Plant Molecular Biology 60: 343-363.
Jiang K. Ballinger T, Li, D, Zhang, S, Feldman LJ (2006) A Role for Mitochondria in the Establishment and Maintenance of the Maize Root Quiescent Center. Plant Physiol. 140: 1118-1125.
Jiang, K, Schwarzer, C, Lally, E, Zhang, S, Ruzin, S, Machen T, Remington, SJ and Feldman LJ . (2006). Expression and characterization of a redox-sensing Green Fluorescent protein (reduction-oxidation-sensitive green fluorescent protein) in Arabidopsis. Plant Physiol. 141: 397–403.
Kim K, Zhang S, Jiang K, Cai L, Lee I-B, Feldman L.J, Huang H 2007. Measuring similarities between gene expression profiles through new data transformations. BMC Bioinformatics, 8:29-43.
Jiang K, Zhu T, Diao Z, Huang H, Feldman LJ 2010. The maize root stem cell niche: a partnership between two sister cell populations. Planta 231, 411-424
Rosenwasswer S, Rot I, Meyer AJ, Feldman L, Jiang K, Friedman H. 2010 A fluorometer-based method for monitoring oxidation of redox-sensitive GFP (roGFP) during development and extended dark stress. Physiologia Plantrum 138, 493-502.
De Tullio MC, Jiang K, Feldman L 2010. Redox regulation of root apical meristem organization: connecting root development to its environment. Plant Physiology and Biochemistry 48, 328-336.
Meng L, Wong JH, Feldman LJ, Lemaux PG, Buchanan BB 2010. A membrane-associated thioredoxin required for plant growth moves from cell-to-cell suggestive of a role in intercellular communication. PNAS 107, 3900-3905.
Jubany-Mari T, Alegre-Battle L, Jiang K and Feldman LJ 2010. Use of a redox-sensing GFP(c-roGFP1) for real-time monitoring of cytosol redox status in Arabidopsis thaliana water-stressed plants. FEBS letters 584, 889-897.
Jiang K, Feldman LJ 2010. Positioning of the auxin maximum affects the character of cells occupying the root stem cell niche. Plant Signaling and Behavior 5, 1-3.
Meng L, Feldman LJ 2010. The roles of different CLE domains in Arabidopsis CLE polypeptide activity and functional specificity. Molecular Plant 3, 760-772.
Meng L, Feldman, LJ 2010. CLE14/CLE20 peptides may interact with CLAVATA2/CORYNE receptor-like kinases to irreversibly inhibit cell division in the root meristem of Arabidopsis. Planta, in press.
Honors and Awards
Distinguished Teaching Award - University of California, Berkeley - 1996
CNR Teaching Award - College of Natural Resources - 1992