Hevein is a chitin-binding protein that is present in laticifers of the rubber tree (Hevea brasilensis

Reactive oxygen species are common causes of cellular damages in all aerobic organisms. In Escherichia coli, the oxyR gene product is a positive regulator of the oxyR regulon that is induced in response to H202 stress. To identify genes involved in counteracting oxidative stress in plants, we transformed a AoxyR mutant of E. coli with an Arabidopsis thaliana cDNA library and selected for clones that restored the ability of the AoxyR mutant to grow in the presence of H202. Using this approach, we isolated a cDNA that has strong homology with the annexin super-gene family. The complemented mutant showed higher catalase activity. mRNA expression of the annexin gene in A. thaliana was higher in roots as compared with other organs and was also increased when the plants were exposed to H202 stress or salicylic acid. Based on the results presented in this study, we propose a novel physiological role for annexin in counteracting H202 stress.

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Hevea brasiliensis is the major producer of natural rubber which is cis-1,4-polyisoprene. The enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) is involved in the biosynthesis of rubber and other plant products. We have used a hamster HMGR cDNA clone as a heterologous hybridization probe to isolate and characterize cDNA and genomic clones of HMGR from H. brasiliensis. Sequence analysis revealed that these clones fall into two different classes, HMGR1 and HMGR2. Comparison of the two classes shows 86% nucleotide sequence homology and 95% amino acid homology. The carboxy-termini of Hevea HMGRs are highly homologous to those of hamster, yeast and Arabidopsis HMGR. The amino-terminus of Hevea HMGR contains two potential membrane-spanning domains as in Arabidopsis HMGR while seven such domains are found in the HMGRs of other organisms. The apparent molecular mass of Hevea HMGR was estimated in western blot analysis to be 59 kDa. Northern blot analysis indicated that the HMGR1 transcript of 2.4 kb is more highly-expressed in laticifer than in leaf. Genomic Southern analysis using 3'-end cDNA probes indicates the presence of at least two HMGR genes in Hevea.