Gene profiling of a compatible interaction between Phytophthora infestans and Solanum tuberosum suggests a role for carbonic anhydrase.

Late blight of potato, caused by the oomycete pathogen Phytophthora infestans, is a devastating disease that can cause the rapid death of plants. To investigate the molecular basis of this compatible interaction, potato cDNA microarrays were utilized to identify genes that were differentially expressed in the host during a compatible interaction with P. infestans. Of the 7,680 cDNA clones represented on the array, 643 (12.9%) were differentially expressed in infected plants as compared with mock-inoculated control plants. These genes were classified into eight groups using a nonhierarchical clustering method with two clusters (358 genes) generally down-regulated, three clusters (241 genes) generally up-regulated, and three clusters (44 genes) with a significant change in expression at only one timepoint. Three genes derived from two down-regulated clusters were evaluated further, using reverse transcription real-time polymerase chain reaction analysis. For these analyses, both incompatible and compatible interactions were included to determine if suppression of these genes was specific to compatibility. One gene, plastidic carbonic anhydrase (CA), was found to have a very different expression pattern in compatible vs. incompatible interactions. Virus-induced gene silencing was used to suppress expression of this gene in Nicotiana benthamiana. In CA-silenced plants, the pathogen grew more quickly, indicating that suppression of CA increases susceptibility to P. infestans.

Caspase-like protease involvement in the control of plant cell death.

Cell death as a highly regulated process has now been recognized to be an important, if not essential, pathway that is ubiquitous in all multicellular eukaryotes. In addition to playing key roles in the morphogenesis and sculpting of the organs to give rise to highly specialized forms and shapes, cell death also participates in the programmed creation of specialized cell types for essential functions such as the selection of B cells in the immune system of mammals and the formation of tracheids in the xylem of vascular plants. Studies of apoptosis, the most well-characterized form of animal programmed cell death, have culminated in the identification of a central tripartite death switch the enzymatic component of which is a conserved family of cysteine proteases called caspases. Studies in invertebrates and other animal models suggest that caspases are conserved regulators of apoptotic cell death in all metazoans. In plant systems, the identities of the main executioners that orchestrate cell death remain elusive. Recent evidence from inhibitor studies and biochemical approaches suggests that caspase-like proteases may also be involved in cell death control in higher plants. Furthermore, the mitochondrion and reactive oxygen species may well constitute a common pathway for cell death activation in both animal and plant cells. Cloning of plant caspase-like proteases and elucidation of the mechanisms through which mitochondria may regulate cell death in both systems should shed light on the evolution of cell death control in eukaryotes and may help to identify essential components that are highly conserved in eukaryotes.

Die and let live - programmed cell death in plants.

Cysteine and serine proteases are prominent players in the control of developmental and pathogen-activated cell deaths in plants. Ethylene, salicylic acid, the small G-protein Rac, calcium and reactive oxygen species are recurring mediators of death signaling. Lastly, the mitochondrion has emerged in both plant and animal systems as a 'central depot' that interprets multiple signals and in some instances determines the fate of the cell.

Caspases and programmed cell death in the hypersensitive response of plants to pathogens.

The hypersensitive response (HR) is induced by certain plant pathogens and involves programmed cell death (PCD) to restrict the spread of pathogens from the infection site [1]. Concurrent with the induction of cell death, the host activates a defense response [2]. The cell death associated with the HR in several plant-pathogen systems has morphological similarities to animal apoptosis [3,4], which suggests that cell death mechanisms in plants and animals may share common components that lead to similar cellular events. Caspases are conserved cysteine proteases that regulate animal PCD [5]; caspase activity or an involvement of caspases in cell death has yet to be reported in plants. In this work, we investigated the participation of caspases in HR cell death. Caspase-specific peptide inhibitors, Ac-YVAD-CMK [6] and Ac-DEVD-CHO [7], could abolish bacteria-induced plant PCD but did not significantly affect the induction of other aspects of HR, such as the expression of defense genes. This result confirmed our previous model that cell death can be uncoupled from defense gene activation during HR [8]. Caspase-like proteolytic activity was detected in tobacco tissues that were developing HR following infection with tobacco mosaic virus (TMV). Our results provide evidence for the presence of caspase-like plant protease(s) that participate in HR cell death.

Pathogen-induced programmed cell death in plants, a possible defense mechanism.

As much as the definition of life may be controversial, the definition of death also may prove problematic. In recent years it became apparent that the death of a living cell may follow more than one possible scenario: it may result from an externally applied physical injury (an accidental death), or it may be the outcome of activating an internal pathway for cell suicide (a programmed death). That cells can participate in their own execution may indicate that certain types of cell deaths that were previously considered to be caused by foreign agents such as pathogens or drugs may actually result from the activation of a programmed cell death pathway that is normally latent in cells. Here, we describe the activation of such a cell suicide pathway in plant cells upon the recognition of an invading pathogen. We discuss the possible use of this pathway as a defense mechanism against infection and the possibility that in many ways the use of this type of cell death in plants is functionally analogous to that used by mammalian cells in response to infection by pathogens.

Structure of the dehydrin tas14 gene of tomato and its developmental and environmental regulation in transgenic tobacco.

We have isolated a genomic clone encoding tomato TAS14, a dehydrin that accumulates in response to mannitol, NaCl or abscisic acid (ABA) treatment. A fragment of tas14 gene containing the region from -2591 to +162 fused to beta-glucuronidase gene drives ABA- and osmotic stress-induced GUS expression in transgenic tobacco. Histochemical analysis of salt-, mannitol- and ABA-treated plants showed GUS activity mainly localized to vascular tissues, outer cortex and adventitious root meristems, coinciding with the previously observed distribution of TAS14 protein in salt-stressed tomato plants. In addition, GUS activity was also observed in guard cells, trichomes and leaf axils. Developmentally regulated gus expression was studied in unstressed plants and found to occur not only in embryos, but also in flowers and pollen. Tas14 expression in floral organs was confirmed by northern blots of tomato flowers.