A full-length copy of bean leaf chitinase mRNA has been cloned. The 1146-base-pair insert of pCH18 encodes the 27-residue amino-terminal signal peptide of the precursor and 301 residues of the mature protein. Utilizing pCH18 as a hybridization probe, we have shown that the increase in translatable chitinase mRNA seen upon ethylene treatment of bean seedlings is due to a 75-to 100-fold increase in steady-state mRNA levels. Southern blot analysis of bean genomic DNA revealed that chitinase is encoded by a small, multigene family consisting of approximately four members. From our nucleotide sequence analysis of five additional chitinase cDNA clones, it appears that at least two of these genes are expressed. Three of the bean chitinase genes have been isolated from a Sau3A genomic library and partially characterized.The development of disease resistance in higher plants is manifested by the accumulation of a number of host-synthesized polypeptides that are produced in response to pathogen attack. Among these are the following: (i) enzymes involved in the synthesis of phytoalexins (secondary metabolites that are toxic to bacteria and fungi) (1), (ii) enzymes leading to the formation of physical barriers to fungal invasion through modifications of the plant cell wall (2), (iii) inhibitors of serine endoproteases (2, 3), and (iv) lytic enzymes (e.g., chitinase and ,-1,3-glucanase) that are capable of degrading fungal cell walls (4,5). While inhibitor studies indicate that host RNA and protein synthesis are required for the induction of these proteins (6), there is a paucity of information concerning the regulation and expression of the genes involved.

A cDNA clone (pRU8604) encoding an endochitinase from potato (Solanum tuberosum L cv. Russet Burbank) leaves has been isolated and sequenced. The predicted coding region spans 328 amino acids and establishes the complete amino acid sequence for this enzyme (Figure 1). This gene is tightly regulated by the phytohormone ethylene, showing an mduction of approximately 30-fold m young leaves. It has also been demonstrated that this gene is expressed in leaves, roots, stem, and petioles of the mature potato. Although expression can also be detected in tubers, the eevel of induction by ethylene is greatly reduced suggesting that constitutive expression may afford greater pathogen resistance in this organ. Homology comparisons between the prinmary structure of potato sequence with

Chitinase gene expression has been shown to be transcriptionally regulated by a number of inducers, including ethylene, elicitors, and pathogen attack. To investigate the mechanism(s) responsible for induction of chitinase gene expression in response to various stimuli, we have developed a transient gene expression system in bean (Phaseolus vulgaris) protoplasts that is responsive to ethylene and elicitor treatment. This system was used to study the expression of a chimeric gene composed of the 5' flanking sequences of a bean endochitinase gene fused to the reporter gene ,-glucuronidase linked to a 3' fragment from nopaline synthase. Addition of 1-aminocyclopropane-1-carboxylic acid, the direct precursor of ethylene, or elicitors such as chitin oligosaccharides or cell wall fragments derived from Colletotrichum lagenarium, to transformed protoplasts resulted in a rapid and marked increase in the expression of the chimeric gene. The kinetics and dose response for these treatments were similar to those observed for the native gene in vivo. Analyses of 5' deletion mutants in the protoplast system indicated that DNA sequences located between -305 and -236 are important for both ethylene and elicitor induction of the reporter gene.Chitinase, a lytic enzyme found in most higher plants (1, 3), catalyzes the hydrolysis of chitin, a A-( 1,4)-linked polymer of 2-acetamido-2-deoxy-13-D-glucose. Although no endogenous substrate for this enzyme has been found in plants, chitin is a major component of the cell walls of many fungi (31). For this reason, Abeles et al. (1) proposed that chitinase functions as a defense against chitin-containing pathogens. This hypothesis is supported by studies which indicate that chitinase levels are increased in response to pathogen attack (19,20,24,25). In vitro studies have demonstrated further that plant chitinases are capable of hydrolyzing the cell walls ofplant pathogenic fungi (30) and releasing elicitors ofdefense reactions (14). In addition, plants treated with the phytohormone ethylene (1, 3) or elicitors such as isolated fungal cell walls (7,21,22), endogenous plant cell walls (21), or chitin oligosaccharides (14, 23), have also been shown to contain

Hepatic cytokine gene expression is independently stimulated by circulating microbial products and reductions in the cellular O2 supply. Although these stimuli occur sequentially after gram-negative bacteremia, it is unknown whether their interplay augments production of interleukin (IL)-1 by the liver. We studied the effects of intraportal Escherichia coli (EC) bacteremia and secondary constant-flow hypoxia (Po2, approximately 46 Torr for 30 min) on IL-1 alpha and IL-1 beta gene expression in ex situ buffer-perfused rat livers over 180 min (n = 67). At t = 0, normoxic EC and normal saline (NS) controls received 10(9) live EC serotype 055:B5 and 0.9% NaCl, respectively; in livers subjected to EC+hypoxia-reoxygenation (H/R) and NS+H/R, hypoxia began 0.5 h after EC or NS and was followed by 120 min of reoxygenation. Portal and hepatic venous perfusates were serially analyzed for bacterial colony-forming units, O2 uptake, and aspartate aminotransferase. At 60 min (peak hypoxia) and 180 min, cDNAs for IL-1 alpha and IL-1 beta were hybridized to whole liver RNA, and IL-1 beta protein levels in venous perfusates were assessed. Intrahepatic levels of reduced glutathione (GSH) were measured as an index of oxidative stress. Compared with normoxic EC, IL-1 alpha transcripts decreased at 180 min in EC+H/R livers (P < 0.0001) as did IL-1 beta mRNA (P < 0.05), despite similar EC clearance, GSH levels, posthypoxic O2 uptake, and aspartate aminotransferase release. Hepatic secretion of IL-1 beta likewise fell in EC+H/R vs. EC controls (P < 0.005). Prostaglandin H synthase-2 (COX-2) message accumulation was not enhanced by H/R, and indomethacin did not reverse H/R-mediated suppression of IL-1 production. In contrast, H/R-related falls in EC-induced IL-1S expression were reversed by allopurinol or catalase. Thus brief hypoxic stress of the liver causing neither GSH depletion nor functional impairment downregulates postbacteremic IL-1 expression by a mechanism involving O2 radicals but not cyclooxygenase metabolites.

A genomic clone encoding manganese-containing superoxide dismutase (SOD; EC 1.15.1.1) was isolated from a Hevea brasiliensis genomic library made in lambda phage EMBL3 by using a heterologous cDNA probe of MnSOD from Nicotiana plumbaginifolia. The nucleotide sequence of 4968 bp from the genomic clone was determined. Based on the putative translation initiation codon and stop codon, PCR primers were designed and utilized for cloning the full-length cDNA from total mRNA. Of the two distinct cDNAs of MnSOD isolated, MnSOD-A has a perfect match with exons of the nuclear gene, while MnSOD-B has a 90.2% homology and is 6 nucleotides longer than MnSOD-A in the putative transit peptide region. The nuclear gene comprises 6 exons and 5 introns, giving a total length of 3211 bp. The sequences of 1400 bp upstream of the initiation codon and 320 bp downstream of the stop codon were also determined. Southern analysis of genomic DNA from Hevea probed with a genomic fragment indicated there are at least two genes of MnSOD in Hevea. Northern blot analysis showed that MnSOD transcripts were present in all tissues examined (leaf, petiole, root, latex, callus) with young leaves showing the highest levels in intact plants. The transcript level in embryogenic callus was nearly 50-fold higher than in mature leaves. In addition, transcripts of MnSOD could be induced 3- to 5-fold in response to sucrose, ethephon and Murashige-Skoog salts.