Insect regurgitant and wounding elicit similar defense responses in poplar leaves: not something to spit at?

Genome-wide identification, phylogenetic analysis, and expression profiling of glycine-rich RNA-binding protein (GRPs) genes in seeded and seedless grapes (Vitis vinifera)

Glycine-rich RNA-binding proteins (GRPs) are essential for many physiological and biochemical processes in plants, especially the response to environmental stresses. GRPs exist widely in angiosperms and gymnosperms plant species; however, their roles in Vitis vinifera are still poorly understood. To characterize VviGRP gene family, we performed a genomic survey, bioinformatics and expression analysis of VviGRPs in grape. We identified nineteen VviGRPs gene family members. The result of bioinformatics analysis showed their motif distribution, gene structure characteristics and chromosomal locations. Then we carried out synteny and phylogenetic analysis to study the origin and evolutionary relationship of GRPs. Tissue-specific expression analysis showed that VviGRPs have different expression patterns. Meanwhile, we studied expression profiles of seventeen ovule-expressed genes during seed development of stenospermocarpic seedless and seeded grapes, and the result showed that most of them have much higher relative expression levels in stenospermocarpic seedless grapes than that of seeded one before 25 days after full bloom (DAFB). It is suggested that VviGRPs may involve in the seed development process. Taken together, our research indicated that VviGRPs are related to seed development and will be beneficial for further investigations into the seed abortion mechanism under stenospermocarpic grapes.

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The online version contains supplementary material available at 10.1007/s12298-021-01082-3.

Feeding on tea GH19 chitinase enhances tea defense responses induced by regurgitant derived from Ectropis grisescens

Multiple isoforms of chitinases participate in plant defense against outside invaders. However, the functions of hydrolase family 19 (GH19) chitinases on pest control remain largely unknown. Here we reported the isolation and functional analysis of a gene CsChi19, which encodes a GH19 endochitinase protein of 332 amino acid residues from tea plant (Camellia sinensis). CsChi19 expression levels were upregulated in response to mechanical wounding, infestation by two important pests: the tea geometrid Ectropis grisescens and the tea green leafhopper Empoasca (Matsumurasca) onukii, a fungal pathogen Colletotrichum fructicola, and treatment with two phytohormones: jasmonic acid (JA) and salicylic acid. CsChi19 was heterologously expressed in Escherichia coli, and its catalytic function was further elucidated. The protein could hydrolyze colloidal chitin, and the optimum temperature and pH for its activity was 40°C and pH 5.0. CsChi19 were found to be toxic to tea pests when they were fed on artificial diets containing this protein. Interestingly, the regurgitant derived from E. grisescens fed with artificial diets containing CsChi19 protein induced stronger expression of CsMPK3, more JA burst, more accumulation of defense-related secondary metabolites, and more emission of volatiles than the regurgitant derived from E. grisescens fed only with artificial diets. Our results provide first evidence that CsChi19 is involved in mediating a novel defense mechanism of tea plant through altering the composition of the regurgitant.

Root condensed tannins vary over time, but are unrelated to leaf tannins

Although the negative effects of root herbivores on plant fitness are expected to be similar to those of above-ground herbivores, the study of below-ground plant defences is limited compared to the rich literature on above-ground defences. Current theory predicts that concentrations of defensive chemicals above- and below-ground should be correlated, as the evolutionary drivers that shape plant defence are similar across the whole plant. We conducted a field study to measure root condensed tannin concentrations in Populus tremuloides, and determine how they related to leaf condensed tannin concentrations, tree position within the stand (edge vs. interior), tree size, and time of year. Overall, root tannin concentrations were substantially lower than leaf tannin concentrations. At individual sampling periods, root and leaf tannin concentrations were uncorrelated with each other, and did not vary with stand position or size. Across the growing season both root and leaf tannin concentrations did show similar trends, with both highest in the early summer, and declining through mid-summer and fall. These results suggest that the mechanisms that influence leaf and root tannin levels in aspen are independent within individual stems, possibly due to different evolutionary pressures experienced by the different tissue types or in response to localized (roots vs. foliage) stressors. However, across individual stems, the similar patterns in chemical defence over time, independent of plant size or stand position indicate that larger scale processes can have consistent effects across individuals within a population, such as the relative investment in defence of tissues in the spring versus the fall. Overall, we conclude that using theories based on above-ground defence to predict below-ground defences may not be possible without further studies examining below-ground defence.

A L-type lectin gene is involved in the response to hormonal treatment and water deficit in Volkamer lemon

Combination of biotic and abiotic stress is a major challenge for crop and fruit production. Thus, identification of genes involved in cross-response to abiotic and biotic stress is of great importance for breeding superior genotypes. Lectins are glycan-binding proteins with a functions in the developmental processes as well as in the response to biotic and abiotic stress. In this work, a lectin like gene, namely ClLectin1, was characterized in Volkamer lemon and its expression was studied in plants exposed to either water stress, hormonal elicitors (JA, SA, ABA) or wounding to understand whether this gene may have a function in the response to multiple stress combination. Results showed that ClLectin1 has 100% homology with a L-type lectin gene from C. sinensis and the in silico study of the 5'UTR region showed the presence of cis-responsive elements to SA, DRE2 and ABA. ClLectin1 was rapidly induced by hormonal treatments and wounding, at local and systemic levels, suggesting an involvement in defence signalling pathways and a possible role as fast detection biomarker of biotic stress. On the other hand, the induction of ClLectin1 by water stress pointed out a role of the gene in the response to drought. The simultaneous response of ClLectin1 expression to water stress and SA treatment could be further investigated to assess whether a moderate drought stress may be useful to improve citrus performance by stimulating the SA-dependent response to biotic stress.

Effects of jasmonic acid, branching and girdling on carbon and nitrogen transport in poplar

• Here, we examined the impact of jasmonate (JA) treatment, branching and phloem girdling on ¹³C and ¹⁵N import, invertase activity and polyphenol accumulation in juvenile tissues of unbranched and branched hybrid poplar saplings (Populus nigra × P. deltoides). • The import of ¹³C to juvenile tissues was positively correlated with invertase activity at the treatment site and enhanced by JA. Both invertase activity and ¹³C import were greater in shorter, younger branches and smaller, younger leaves. By contrast, JA treatments, branching and girdling had little or no impact on ¹⁵N import. • In poplar saplings with multiple lateral branches, we observed almost no ¹³C movement from subtending source leaves into lateral branches above them, with or without JA treatment. The presence of potentially competing branches, treated with JA or not, girdled or not, had no impact on carbohydrate (CHO) import or polyphenol accumulation in target branches. • We conclude that poplar branches comprise modules that are relatively independent from each other and from the stem below in terms of CHO movement, carbon-based defence production and response to elicitors. By contrast, branches are closely linked modules in terms of nitrogen movement. This should produce trees that are highly heterogeneous in quality for herbivores.

AtGRP5, a vacuole-located glycine-rich protein involved in cell elongation

Although several glycine-rich protein (GRP) genes were isolated and characterized, very little is known about their function. The primary structure of AtGRP5 from Arabidopsis thaliana has a signal peptide followed by a region with high glycine content. In this work, green fluorescent protein fusions were obtained in order to characterize the sub-cellular localization of the AtGRP5 protein. The results indicated that this protein is the first described vacuolar GRP. Sense, antisense and RNAi transgenic A. thaliana plants were generated and analyzed phenotypically. Plants overexpressing AtGRP5 showed longer roots and an enhanced elongation of the inflorescence axis, while antisense and RNAi plants demonstrated the opposite phenotype. The analysis of a knockout T-DNA line corroborates the phenotypes obtained with the antisense and RNAi plants. Altogether, these results suggest that this vacuolar GRP could be involved in organ growth by promoting cell elongation processes.

Shoot–root defense signaling and activation of root defense by leaf damage in poplarThis article is one of a selection of papers published in the Special Issue on Poplar Research in Canada

Shoot–root systemic defense signaling of hybrid poplar (Populus trichocarpa Torr. & A. Gray × Populus deltoides Bartr. ex Marsh.) was investigated with molecular techniques to extend existing knowledge of poplar defense. Treatment of roots with methyl jasmonate demonstrated that transcripts of PtdTI3, a poplar trypsin inhibitor and marker of poplar defense responses, can be induced in poplar roots as well as leaves. Moreover, simulated herbivory of poplar leaves with methyl jasmonate treatment or wounding with pliers also induced PtdTI3 mRNA in roots, which implies downward, or basipetal, systemic signaling from shoots to roots. In addition, the inducible root-defense response comprised both increased PtdTI3 protein levels and trypsin-inhibitor activity. The inducible systemic response was further investigated with comparative macroarray analyses which indicated that in addition to PtdTI3, other genes respond in roots after wounding and methyl jasmonate treatment of leaves. The majority of the 17 genes encode previously identified leaf herbivory defense genes; however, some genes strongly up-regulated in leaves were not induced in roots. The identification of multiple defense genes that are inducible in roots following leaf damage is clear evidence of a systemic defense response in roots and the presence of basipetal shoot–root defense signaling.

Herbivore-induced volatiles as rapid signals in systemic plant responses: how to quickly move the information?

Plants respond to local herbivory or pathogen infection with phenotypic changes, which reduce the danger of future attack. This so-called induced resistance is usually not restricted to the attacked plant organ but is also expressed in distant, so far undamaged parts of the plant. Signaling compounds such as jasmonic acid and salicylic acid have been discovered that move within the plant via the xylem or the phloem and elicit the resistance, thus acting as plant hormones. We now found that volatiles released in response to herbivore damage are required to elicit extrafloral nectar secretion in other parts of the same plant. Extrafloral nectar attracts ants and other carnivorous arthropods and serves as an effective indirect defense against herbivores. So called green leaf volatiles are released within minutes in response to tissue damage and were among the compounds that induced nectar secretion in yet undamaged parts of the damaged plant, but also in neighboring plants. Being gaseous and transported via the air, green leaf volatiles can serve a rapid within-plant communication, which moves much faster from one plant organ to the other than any plant-internal compound.