Trichoderma spp. are known to produce enzymes with high xylanolytic activity. Different xylanases and various components of their xylanolytic system have been identified and purified. Some of the xylanases have been characterized extensively with respect to their physicochemical, hydrolytic, and molecular properties. Cellulase-free xylanase preparations have been tested successfully in industrial applications such as the prebleaching of kraft pulps in the pulp and paper industry. Future work on understanding the functional significance of xylanase multiplicity, the mechanisms of xylanase prebleaching, and the structural conformation of xylanases could lead to improved or alternative applications of Trichoderma xylanases.

Trichoderma Xylanases, Their Properties and Application

Summary
A long-standing goal in plant research is to optimize the protective function of biochemical agents that impede pest and pathogen attack. Nearly 40 years ago, pathogen-inducible diterpenoid production was described in rice, and these compounds were shown to function as antimicrobial phytoalexins. Using rice and maize as examples, we discuss recent advances in the discovery, biosynthesis, elicitation and functional characterization of monocot terpenoid phytoalexins. The recent expansion of known terpenoid phytoalexins now includes not only the labdane-related diterpenoid superfamily but also casbane-type diterpenoids and β-macrocarpene-derived sequiterpenoids. Biochemical approaches have been used to pair pathway precursors and end products with cognate biosynthetic genes. The number of predicted terpenoid phytoalexins is expanding through advances in cereal genome annotation and terpene synthase characterization that likewise enable discoveries outside the Poaceae. At the cellular level, conclusive evidence now exists for multiple plant receptors of fungal-derived chitin elicitors, phosphorylation of membrane-associated signaling complexes, activation of mitogen-activated protein kinase, involvement of phytohormone signals, and the existence of transcription factors that mediate the expression of phytoalexin biosynthetic genes and subsequent accumulation of pathway end products. Elicited production of terpenoid phytoalexins exhibit additional biological functions, including root exudate-mediated allelopathy and insect antifeedant activity. Such findings have encouraged consideration of additional interactions that blur traditionally discrete phytoalexin classifications. The establishment of mutant collections and increasing ease of genetic transformation assists critical examination of further biological roles. Future research directions include examination of terpenoid phytoalexin precursors and end products as potential signals mediating plant physiological processes.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/tpj.12436

Biosynthesis, elicitation and roles of monocot terpenoid phytoalexins

1. The Plant Hormone, Ethylene. 2. Ethylene in Plant Physiology. 3. Biochemistry of Microbial Production of Ethylene. 4. Factors Affecting Microbial Production of Ethylene In Vitro. 5. Biochemistry of Microbial Production of Ethylene. 6. Ethylene in Symbiosis. 7. Ethylene in Pathogenesis. 8. Ethylene in Agriculture: Synthetic and Natural Sources and Applications.

Ethylene: Agricultural Sources and Applications

We have investigated the abilities of extracellular enzymes from dark-grown cell-suspension cultures of sycamore maple (Acer pseudoplatanus L.) to oxidize monolignols, the precursors for lignin biosynthesis in plants, as well as a variety of other lignin-related compounds. Laccase and peroxidase both exist as a multiplicity of isoenzymes in filtrates of spent culture medium, but their abilities to produce water-insoluble, dehydrogenation polymers (DHPs) from the monolignols (in the presence of hydrogen peroxide for the peroxidase reaction) appear identical whether or not the enzymes are purified from the concentrated filtrates or left in a crude mixture. The patterns of bonds formed in these DHPs are identical to those found in DHPs synthesized using horseradish peroxidase or fungal laccase, and many of these bonds are found in the natural lignins extracted from different plant sources. On the other hand, sycamore maple laccase is very much less active on phenolic substrates containing multiple aromatic rings than is sycamore maple peroxidase. We suggst that whereas laccase may function during the early stages of lignification to polymerize monolignols into oligo-lignols, cell-wall peroxidases may function when H2O2 is produced during the later stages of xylem cell development or in response to environmental stresses.

Extracellular laccases and peroxidases from sycamore maple (Acer pseudoplatanus) cell-suspension cultures. Reactions with monolignols and lignin model compounds

Effective biocontrol strains of Trichoderma virens can induce the production of defense-related compounds in the roots of cotton. Ineffective strains do not induce these compounds to significant levels. This elicittation was found to be heat stable, insoluble in chloroform, passed through a 5K molecular weight cut-off (MWCO) filter, but not a 3K MWCO filter, and was sensitive to treatment by proteinase K. When the active material was subjected to sodium dodecyl sulfate-polyacrylamide gel electrophoresis, several bands were present in the material from biocontrol-active strains that were lacking in inactive strains. When eluted and tested for elicitation activity, with or without renaturation, four bands stimulated cotton terpenoid production. One band showed cross-reaction with an antibody to the ethylene-inducing xylanase from T. viride. Another band of approximately 18 kDa, gave significant stimulation of cotton terpenoid production and increased peroxidase activity in cotton radicles in all tests, with or without renaturation. The 18-kDa protein was subjected to amino-terminal sequence analysis, and the first 19 amino acids at the amino terminus were determined to be DTVSYDTGYDNGSRSLNDV. A database homology search using the BLASTp algorithm showed the highest similarity to a serine proteinase from Fusarium sporotrichioides.

Elicitors of plant defense responses from biocontrol strains of Trichoderma virens

A protein component of Cellulysin is known to induce ethylene biosynthesis in a variety of plant tissues and harbors an endo-beta-1,4-xylanase activity. Antiserum to the native ethylene biosynthesis-inducing xylanase immunoprecipitates both the enzymatic and biological activities. However, antisera raised against either the denatured 22- or 14-kilodalton (kDa) polypeptides comprising the native protein were ineffective in precipitating either activity. All three antibodies recognized the 14- and 22-kDa antigens on immunoblots. Synthesis of a single 22-kDa extracellular polypeptide detectable on immunoblots with the three antisera against the Cellulysin polypeptides was inducible in Trichoderma viride during growth on D-xylose, xylan, or crude cell-wall preparations. Induction was not observed when the fungus was grown on L-xylose, beta-methyl-D-xylose, glucose, or several purified cell-wall polymers, including pectin, polygalacturonate, arabinogalactan, and cellulose. Production of this protein was influenced by substrate concentration and culture pH. When grown in the induction medium, several other species of Trichoderma and Gliocladium also synthesize a 22-kDa xylanase that could be detected on immunoblots and was capable of inducing ethylene biosynthesis. Isoelectric focusing demonstrated that the cross-reactive polypeptides from these fungi exist as isoforms. The primary form had a pI of 9.4, and less abundant forms focused at pI 8.4 and lower. Culture filtrates of two plant pathogens, Fusarium oxysporum f. sp. pisi and Macrophomina phaseolina, also contained ethylene biosynthesis-inducing and xylanase activities, as well as a 22-kDa cross-reactive polypeptide. M. phaseolina filtrates also contained substantial amounts of a 14-kDa polypeptide similar to that found in Cellulysin

H.R. Gamble

Papers

The ethylene biosynthesis-inducing xylanase: its induction in Trichoderma viride and certain plant pathogens