Environmental cDNA analysis of the genes involved in lignocellulose digestion in the symbiotic protist community of Reticulitermes speratus

To clarify the lignocellulolytic process of the lower termite symbiotic protistan system, we constructed a cDNA library from an as yet uncultivated symbiotic protist community of the lower termite Reticulitermes speratus. The library was constructed by the biotinylated CAP trapper method and analyzed by one-pass sequencing. Phylogenetic analysis of actin orthologs confirmed that the resulting library reflected the intact organismal and mRNA composition of the symbiotic system. The contents of the library included abundant numbers of lignocellulolytic genes of the glycosyl hydrolase family orthologs (families 3, 5, 7, 8, 10, 11, 26, 43, 45 and 62). Our results clearly indicated that a multiple family of glycosyl hydrolase enzymes was involved in the protistan cellulose degradation system. The data also suggested that the most extensively expressed enzyme was glycosyl hydrolase family 7, a cellobiohydrolase ortholog. This family of enzymes enables the degradation of crystalline cellulose, the principal component of wood biomass.     

A Possible Regulation of Ethylene Production by the Epidermis in Mung Bean Hypocotyl Sections

IAA-induced and l-aminocyclopropane-l-carboxylic acid (ACC)-dependentethylene production in etiolated mung bean (Vigna radiata [L]Wilczek) hypocotyl sections does not occur in epidermal cells(Todaka and Imaseki 1985). Mung bean hypocotyls contain a proteinwhich inhibits auxin-induced ethylene biosynthesis in hypocotylsections (Sakai and Imaseki 1975a, b). This inhibitory proteinwas also found to inhibit ACC-dependent ethylene productionin hypocotyl sections, but not in hypocotyl sections from whichthe epidermis had been removed. Uptake of ACC by both unpeeledand peeled sections was not inhibited by the protein. Similarly,IAA-induced ethylene production was inhibited by the proteinin unpeeled hypocotyl sections, but not in peeled sections.The protein was not inactivated in peeled sections, as proteinsynthesis by peeled sections was inhibited to the same extentas in unpeeled sections. The protein inhibited incorporationof 3,4-[¹⁴C]-methionine into ACC and ethylene in unpeeled sections,but not in peeled sections, whereas oxidation of the labeledmethionine into CO₂ was inhibited by the protein to a similarextent in both types of hypocotyl sections. KCN, a potent inhibitorof ethylene production, inhibited both IAA-induced and ACC-dependentethylene production in both peeled and unpeeled hypocotyl sections.It is likely that the epidermis plays some role in controllingethylene production which occurs in stem cells other than epidermalcells. (Received July 16, 1985; Accepted October 21, 1985)     

Overproduction of the Membrane-bound Receptor-like Protein Kinase 1, RPK1, Enhances Abiotic Stress Tolerance in Arabidopsis

RPK1 (receptor-like protein kinase 1) localizes to the plasma membrane and functions as a regulator of abscisic acid (ABA) signaling in Arabidopsis. In our current study, we investigated the effect of RPK1 disruption and overproduction upon plant responses to drought stress. Transgenic Arabidopsis overexpressing the RPK1 protein showed increased ABA sensitivity in their root growth and stomatal closure and also displayed less transpirational water loss. In contrast, a mutant lacking RPK1 function, rpk1-1, was found to be resistant to ABA during these processes and showed increased water loss. RPK1 overproduction in these transgenic plants thus increased their tolerance to drought stress. We performed microarray analysis of RPK1 transgenic plants and observed enhanced expression of several stress-responsive genes, such as Cor15a, Cor15b, and rd29A, in addition to H₂O₂-responsive genes. Consistently, the expression levels of ABA/stress-responsive genes in rpk1-1 had decreased compared with wild type. The results suggest that the overproduction of RPK1 enhances both the ABA and drought stress signaling pathways. Furthermore, the leaves of the rpk1-1 plants exhibit higher sensitivity to oxidative stress upon ABA-pretreatment, whereas transgenic plants overproducing RPK1 manifest increased tolerance to this stress. Our current data suggest therefore that RPK1 overproduction controls reactive oxygen species homeostasis and enhances both water and oxidative stress tolerance in Arabidopsis.