The mechanisms underlying the organization of cell layers in the development of plant organs are not fully understood. In order to gain insight into the progression of events that lead to differentiation of peripheral cell layers, GC Ingram and associates at the ICMB, the University of Edinburgh, cloned the ARABIDOPSIS CRINKLY4 gene and studied its expression in fast dividing cells in various meristematic zones.

In the September, 03 issue of Development (vol 130:4249-58), the above authors report that they have characterized the ARABIDOPSIS CRINKLY4 gene. Their study reveals that this gene encodes a functional kinase and that it is expressed in the L1 cell layer of most of the meristematic and organ primordial tissues such as the ovule integuments. Using insertional mutations, they were able to show that this gene regulates cellular organization of certain organ development such as sepal margins and the integument around the nucellar tissue. The abundant presence of the receptor kinase in anticlinal and the inner periclinal plasma membrane of 'exterior' cells indicates that the above gene plays a significant role in certain developmental process restricted to outer meristematic cell layers. Based on their findings, the authors propose that ARABIDOPSIS CRINKLY4 organizes and maintains external cell layers in organs of vital importance by receiving and transmitting signals from adjoining L1 cell layers alone or possibly both from L1- and underlying layers of cells.

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It is known for quite some time that calcium plays a significant role in signal transduction pathways. Calcium critically influences the expression of stress-related genes. However, the molecular mechanism underlying calcium function has not yet been worked out. It is believed that in the cytosol there are sensor molecules such as calcium binding proteins that recognize calcium changes within the cell. It is also known that there are calcineurin B-like (CBL) protein families that act as calcium sensors in plants.

In the August, 03 issue of Plant Cell (vol.15:1833-45), a team of scientists led by S. Luan at the Department of Plant and Microbial Biology, UCB, report that CBL1, a member of the CBL family CBL1, is highly stress sensitive and is induced by multiple stress signals. An increase in the CBL1-encoded protein level in transgenic Arabidopsis plants was found to modify the stress response pathways in these plants. The authors studies further revealed that this gene acted differently under different kinds of stress. For example, CBL1 positively regulates the drought-induced gene expression but negatively regulate the cold-responsive genes. Consistent with this, transgenics over-expressing CBL1 became more tolerant to salt and drought, while their susceptibility to freezing temperatures increased. Conversely, the cold tolerance capacity of cbl1 null mutants in Arabidopsis plants increased, while these mutants were more susceptible in the drought and saline environment. The authors concluded that depending upon the environment, CBL1 acts as a positive or a negative regulator of stress responses.

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Phytophthora infestans causes late blight disease of potato. In certain years the damage is very severe. Fungicide treatment has thus far been the only solution to contain this ravaging disease in the USA and other developed countries. No potato cultivars in the USA are known to contain genes that confer resistance to late blight. The absence of a resistant potato variety prompted a research team led by J. Jiang and J.P. Helgeson at the University of Wisconsin, Madison (WUM) to survey a wide range of Solanum species, searching for genes that would protect the potato crop against this deadly disease. When laboratory tests revealed that S. bulbocastanum, a wild diploid potato species is highly resistant to all known races of P. infestans, they cloned the gene and designated it the RB gene. The effective and long-lasting resistance ability of this diploid species was also demonstrated in the field. 

In the July 18, 2003, online publication of PNAS, the 12-member team affiliated to USDA, UCD, UWM and two other institutions, report the cloning of the major resistance gene RB in S. bulbocastanum. The authors used a combination of techniques: a map-based method supported by a long-range (LR)-PCR strategy. Their study revealed a cluster of four resistance genes of the CC-NBS-LRR (coiled coil-nucleotide binding site-Leu-rich repeat) class. They were located within the genetically mapped RB region. Transgenics transformed with one of these four genes showed late blight resistance over a wide range of pathogen races. Thus, the above investigation yielded the cloned RB gene - a new resistance source for developing late blight resistant potato varieties. Another byproduct of this investigation has been the demonstration that LR-PCR method can be used to isolate genes that cannot be maintained in the bacterial artificial chromosome system.