Kunitz-type trypsin inhibitor gene family in Arabidopsis and Populus trichocarpa and its expression response to wounding and herbivore in Populus nigra

Trypsin inhibitors (TIs) play important roles in plant defense against biotic stresses. In this work, we first characterized the KTI gene families in the herbaceous model system, Arabidopsis thaliana, and the woody model system, Populus trichocarpa. Genomic analysis of AtKTIs and PtKTIs including phylogenetic relationship, gene structure, and motif preservation was presented. The temporal and spatial expression pattern of AtKTI genes under biotic and abiotic stresses has been performed by mining the publicly available microarray data. Unlike Populus, the absence of AtKTI induction under herbivore attack suggested that AtKTIs may not be closely related to herbivore defense in this plant species. In order to assess the potential of PtKTI as target genes for genetic improvement of the biotic resistance in plant species of high economic impact, we isolated KTI complementary DNAs from Populus nigra on a genome-wide scale and analyzed their respective response to Apocheima cinerarius Erschoff and mechanical wounding. A basically similar subset of PnKTIs was shown to be rapidly induced by both treatments in this study, though quantitatively distinct. This study revealed a different collection of wound- and herbivore-induced P. nigra KTI genes from those reported previously for hybrid poplar infested with Malacosoma disstri. Our data demonstrated that Populus could deploy KTI genes actively and selectively in an insect-specific manner. While KTI genes constitute good candidates for genetic engineering to improve biotic resistance in transgenic plant, their selection should be herbivore-oriented to obtain sufficient effects.     

PAL-mediated SA biosynthesis pathway contributes to nematode resistance in wheat

The pathogen cereal cyst nematode (CCN) is deleterious to Triticeae crops and is a threat to the global crop yield. Accession no. 1 of Aegilops variabilis, a relative of Triticum aestivum (bread wheat), is highly resistant to CCN. Our previous study demonstrated that the expression of the phenylalanine ammonia lyase (PAL) gene AevPAL1 in Ae. variabilis is strongly induced by CCN. PAL, the first enzyme of phenylpropanoid metabolism, is involved in abiotic and biotic stress responses. However, its role in plant–CCN interaction remains unknown. In the present study, we proved that AevPAL1 helps to confer CCN resistance through affecting the synthesis of salicylic acid (SA) and downstream secondary metabolites. The silencing of AevPAL1 increased the incidence of CCN infection in roots and decreased the accumulation of SA and phenylalanine (Phe)-derived specialized metabolites. The exogenous pre-application of SA also improved CCN resistance. Additionally, the functions of PAL in phenylpropanoid metabolism correlated with tryptophan decarboxylase (TDC) functioning in tryptophan metabolism pathways. The silencing of either AevPAL1 or AevTDC1 exhibited a concomitant reduction in the expression of both genes and the contents of metabolites downstream of PAL and TDC. These results suggested that AevPAL1, possibly in coordination with AevTDC1, positively contributes to CCN resistance by altering the downstream secondary metabolites and SA content in Ae. variabilis. Moreover, AevPAL1 overexpression significantly enhanced CCN resistance in bread wheat and did not exhibit significant negative effects on yield-related traits, suggesting that AevPAL1 is valuable for the genetic improvement of CCN resistance in bread wheat.     

An assessment of the biotechnological use of hemoglobin modulation in cereals

Non‐symbiotic hemoglobin (nsHb) genes are ubiquitous in plants, but their biological functions have mostly been studied in model plant species rather than in crops. nsHb influences cell signaling and metabolism by modulating the levels of nitric oxide (NO). Class 1 nsHb is upregulated under hypoxia and is involved in various biotic and abiotic stress responses. Ectopic overexpression of nsHb in Arabidopsis thaliana accelerates development, whilst targeted overexpression in seeds can increase seed yield. Such observations suggest that manipulating nsHb could be a valid biotechnological target. We studied the effects of overexpression of class 1 nsHb in the monocotyledonous crop plant barley (Hordeum vulgare cv. Golden Promise). nsHb was shown to be involved in NO metabolism in barley, as ectopic overexpression reduced the amount of NO released during hypoxia. Further, as in Arabidopsis, nsHb overexpression compromised basal resistance toward pathogens in barley. However, unlike Arabidopsis, nsHb ectopic overexpression delayed growth and development in barley, and seed specific overexpression reduced seed yield. Thus, nsHb overexpression in barley does not seem to be an efficient strategy for increasing yield in cereal crops. These findings highlight the necessity for using actual crop plants rather than laboratory model plants when assessing the effects of biotechnological approaches to crop improvement.     

Ectopic Expression of StERF94 Transcription Factor in Potato Plants Improved Resistance to Fusarium solani Infection

ERF proteins (ethylene-responsive factors), which belong to the AP2/ERF superfamily, play essential roles in plant development, growth, and response to abiotic and biotic constraints. In a previous study, we cloned a cDNA encoding the StERF94 factor from potato plants and the phylogenetic analyses showed that it belongs to group IX of the ERF family. Genes of this group are known to be involved in plant response to biotic stress. The StERF94 cDNA was overexpressed in transgenic potato plants and the resulting transgenic plants showed a high tolerance to salinity. In this study, we investigated the response of StERF94 transgenic plants to biotic stress by evaluating their resistance to Fusarium solani infection. A significant enhanced resistance to the fungus was noticed in the transgenic plants which displayed limited malondialdehyde and H₂O₂ production and increasing antioxidant enzyme activities. Our findings also revealed that overexpression of StERF94 in potato enhanced expression of relevant defense genes like those encoding PR proteins (pathogenesis related) which led to a protection against disease propagation and reduction of fungus development in plant tissues.

     

Functional analysis of endo‐1,4‐β‐glucanases in response to Botrytis cinerea and Pseudomonas syringae reveals their involvement in plant–pathogen interactions

Plant cell wall modification is a critical component in stress responses. Endo‐1,4‐β‐glucanases (EGs) take part in cell wall editing processes, e.g. elongation, ripening and abscission. Here we studied the infection response of Solanum lycopersicum and Arabidopsis thaliana with impaired EGs. Transgenic TomCel1 and TomCel2 tomato antisense plants challenged with Pseudomonas syringae showed higher susceptibility, callose priming and increased jasmonic acid pathway marker gene expression. These two EGs could be resistance factors and may act as negative regulators of callose deposition, probably by interfering with the defence‐signalling network. A study of a set of Arabidopsis EG T‐DNA insertion mutants challenged with P. syringae and Botrytis cinerea revealed that the lack of other EGs interferes with infection phenotype, callose deposition, expression of signalling pathway marker genes and hormonal balance. We conclude that a lack of EGs could alter plant response to pathogens by modifying the properties of the cell wall and/or interfering with signalling pathways, contributing to generate the appropriate signalling outcomes. Analysis of microarray data demonstrates that EGs are differentially expressed upon many different plant–pathogen challenges, hormone treatments and many abiotic stresses. We found some Arabidopsis EG mutants with increased tolerance to osmotic and salt stress. Our results show that impairing EGs can alter plant–pathogen interactions and may contribute to appropriate signalling outcomes in many different biotic and abiotic plant stress responses.     

Abiotic and Biotic Stresses and Changes in the Lignin Content and Composition in Plants

Lignin is a polymer of phenylpropanoid compounds formed through a complex biosynthesis route, represented by a metabolic grid for which most of the genes involved have been sequenced in several plants, mainly in the model-plants Arabidopsis thaliana and Populus. Plants are exposed to different stresses, which may change lignin content and composition. In many cases, particularly for plant-microbe interactions, this has been suggested as defence responses of plants to the stress. Thus, understanding how a stressor modulates expression of the genes related with lignin biosynthesis may allow us to develop study-models to increase our knowledge on the metabolic control of lignin deposition in the cell wall. This review focuses on recent literature reporting on the main types of abiotic and biotic stresses that alter the biosynthesis of lignin in plants.