Because lignin limits the use of wood for fiber, chemical, and energy production, strategies for its downregulation are of considerable interest. We have produced transgenic aspen (Populus tremuloides Michx.) trees in which expression of a lignin biosynthetic pathway gene Pt4CL1 encoding 4-coumarate:coenzyme A ligase (4CL) has been downregulated by antisense inhibition. Trees with suppressed Pt4CL1 expression exhibited up to a 45% reduction of lignin, but this was compensated for by a 15% increase in cellulose. As a result, the total lignin–cellulose mass remained essentially unchanged. Leaf, root, and stem growth were substantially enhanced, and structural integrity was maintained both at the cellular and whole-plant levels in the transgenic lines. Our results indicate that lignin and cellulose deposition could be regulated in a compensatory fashion, which may contribute to metabolic flexibility and a growth advantage to sustain the long-term structural integrity of woody perennials.

Biotechnology on genetic control of lignin biosynthesis in trees -Repression of lignin biosynthesis promotes cellulose accumulation and growth in transgenic trees-

Arbuscular mycorrhizal fungi act as biostimulants in horticultural crops

A critical review on effects, tolerance mechanisms and management of cadmium in vegetables.

Heavy metals and metalloids: Sources, risks and strategies to reduce their accumulation in horticultural crops

Arbuscular mycorrhizal symbioses that involve most plants and Glomeromycota fungi are integral and functional parts of plant roots In these associations, the fungi not only colonize the root cortex but also maintain an extensive network of hyphae that extend out of the root into the surrounding environment These external hyphae contribute to plant uptake of low mobility nutrients, such as P, Zn, and Cu Besides improving plant mineral nutrition, arbuscular mycorrhizal fungi (AMF) can alleviate heavy metal (HM) toxicity to their host plants HMs, such as Cu, Zn, Fe, and Mn, play essential roles in many biological processes but are toxic when present in excess This makes their transport and homeostatic control of particular importance to all living organisms AMF play an important role in modulating plant HM acquisition in a wide range of soil metal concentrations and have been considered to be a key element in the improvement of micronutrient concentrations in crops and in the phytoremediation of polluted soils In the present review, we provide an overview of the contribution of AMF to plant HM acquisition and performance under deficient and toxic HM conditions, and summarize current knowledge of metal homeostasis mechanisms in arbuscular mycorrhizas

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The heavy metal paradox in arbuscular mycorrhizas: from mechanisms to biotechnological applications

Polygalacturonase inhibiting proteins (PGIPs) are cell wall proteins that inhibit the pectin-depolymerizing activity of polygalacturonases secreted by microbial pathogens and insects. These ubiquitous inhibitors have a leucine-rich repeat structure that is strongly conserved in monocot and dicot plants. Previous reviews have summarized the importance of PGIP in plant defense and the structural basis of PG-PGIP interaction; here we update the current knowledge about PGIPs with the recent findings on the composition and evolution of pgip gene families, with a special emphasis on legume and cereal crops. We also update the information about the inhibition properties of single pgip gene products against microbial PGs and the results, including field tests, showing the capacity of PGIP to protect crop plants against fungal, oomycetes and bacterial pathogens.

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An update on polygalacturonase-inhibiting protein (PGIP), a leucine-rich repeat protein that protects crop plants against pathogens.

Physiological, biochemical, metabolite changes and gene expression analysis of greenhouse tomato (Solanum lycopersicumL.) were investigated in two grafting combinations (self-grafted ‘Ikram’ and ‘Ikram’ grafted onto interspecific hybrid rootstock ‘Maxifort’), with and without arbuscular mycorrhizal (AM), exposed to 0 and 25 µM Cd. Tomato plants responded to moderate Cd concentration by decreasing yield and crop growth parameters due to the accumulation of Cd in leaf tissue, inhibition of the PS II activity, reduced nutrients translocation, and also to the oxidative stress as evidenced by enhanced hydrogen peroxide (H2O2) generation, ion leakage and lipid peroxidation. AM inoculation significantly enhanced the metal concentration in shoots and reduced growth and yield. The Ikram/Maxifort combination induced higher antioxidant enzymes, higher accumulation of proline and reduction of lipid peroxidation products. This suggests that the use of Maxifort rootstock in tomato has a high reactive oxygen species scavenging activity since lower H2O2 concentrations were observed in the presence of Cd. The higher crop performance of Ikram/Maxifort in comparison to Ikram/Ikram combination was also due to the improved nutritional status (higher P, K, Ca, Fe, Mn, and Zn) and increased availability of metabolites involved in cadmium tolerance (phytochelatin PC2 and fructans inulins). The up-regulation of LeNRAMP3 gene in leaf of Ikram/Maxifort could explain the better nutritional status of interspecific grafting combination (higher Fe, Mn, and Zn).

Insight into the role of grafting and arbuscular mycorrhiza on cadmium stress tolerance in tomato.

The 4-coumarate-CoA ligases (4CL) contribute in channelizing flux of different phenylpropanoid biosynthetic pathways. Expression of 4CL is optimized at developmental stages and in response to environmental triggers such as biotic and abiotic stresses. The enzyme is valuable in metabolic pathway engineering for curcuminoids, resveratrol, biofuel production and nutritional improvement. Vigorous analysis of regulation at functional and expression level is obligatory to attain efficient commercial production of candidate metabolites using 4CL. Phenylpropanoid pathway provides precursors for numerous secondary metabolites in plants. In this pathway, 4-coumarate-CoA ligase (EC 6.2.1.12, 4CL) is the main branch point enzyme which generates activated thioesters. Being the last enzyme of three shared common steps in general phenylpropanoid pathway, it contributes to channelize precursors for different phenylpropanoids. In plants, 4CL enzymes are present in multiple isoforms and encoded by small gene family. It belongs to adenylate-forming enzyme family and catalyzes the reaction that converts hydroxy or methoxy cinnamic acid derivatives to corresponding thioesters. These thioesters are further utilized for biosynthesis of phenylpropanoids, which are known for having numerous nutritional and medicinal applications. In addition, the 4CL enzymes have been characterized from various plants for their role in plant physiology or in biotic and abiotic stresses. Furthermore, specific isoforms are differentially regulated upon exposure to diverse stimuli leading to flux diversion toward the particular metabolite biosynthesis. Evolutionary studies showed that 4CL separately evolved after monocot and dicot segregation. Here, we provide a comprehensive review on 4CL, which includes evolution, function, gene/protein structure, role in metabolite biosynthesis and cellular partition, and their regulation. Based on the available data, we have explored the scope for pathway engineering by utilizing 4CL enzymes.

Structural, functional and evolutionary diversity of 4-coumarate-CoA ligase in plants

Sugarcane borers are the major biotic pest in sugarcane that accounts nearly 25-30% yield loses Most of the present sugarcane varieties are not resistant to borers Development of borer resistance in sugarcane through transgenic technology could be the best approach Cry series of genes are known for development of insect pest resistance in plants in particular for the most damaging order 'Lepidoptera' The sugarcane (Saccharum hybrids) genotype CoC671 was transformed by Agrobacterium mediated method Cry 1Aa3 gene driven by CaMV35S promoter and Ocs terminator with selectable marker nptII driven by Nos promoter and terminator harboring in binary vector pBinAR was transformed into Agrobacterium tumefaciens strain EHA 105 was used in sugarcane transformation Young leaf roll discs were infected and regenerated plants were obtained in one step after infection with minimal callus phase Three to four shoots per explant were developed after 7-10 days incubation Regenerated shoots were allowed to grow further Two months old putative transgenic plants were taken for molecular characterization Out of 65 plants tested by PCR, 24 plants were positive for Cry1Aa3 gene This represents nearly 28% of the transformation efficiency All these plants were analyzed by Southern blot hybridization for integration of the inserted gene Four plants showed single copy number and another two showed more than two integrations All those 24 plants that are positive by PCR were subjected to ELISA test for expression of foreign protein It was observed that four transgenic plants showed around ten-fold high level expression and another two plants showed with moderate levels, 3-5 fold expression

Raviraj M. Kalunke

Papers

An update on polygalacturonase-inhibiting protein (PGIP), a leucine-rich repeat protein that protects crop plants against pathogens.

Insight into the role of grafting and arbuscular mycorrhiza on cadmium stress tolerance in tomato.

Structural, functional and evolutionary diversity of 4-coumarate-CoA ligase in plants

Agrobacterium mediated transformation of sugarcane for borer resistance using Cry 1Aa3 gene and one-step regeneration of transgenic plants

Detection of ciprofloxacin residues in cow milk: A novel and rapid optical β-galactosidase-based screening assay