Search Results (6)

Although phloem-feeding insects such as aphids can cause significant damage to plants, relatively little is known about early plant defenses against these insects. As a first line of defense, legumes can stop the phloem mass flow through a conformational change in phloem proteins known as forisomes in response to Ca²⁺ influx. However, specialized phloem-feeding insects might be able to suppress the conformational change of forisomes and thereby prevent sieve element occlusion. To investigate this possibility, we triggered forisome dispersion through application of a local heat stimulus to the leaf tips of pea (Pisum sativum), clover (Trifolium pratense) and broad bean (Vicia faba) plants infested with different pea aphid (Acyrthosiphon pisum) host races and monitored forisome responses. Pea aphids were able to suppress forisome dispersion, but this depended on the infesting aphid host race, the plant species, and the age of the plant. Differences in the ability of aphids to suppress forisome dispersion may be explained by differences in the composition and quantity of the aphid saliva injected into the plant. Various mechanisms of how pea aphids might suppress forisome dispersion are discussed. Full article

In plants, phloem is not only a vital structure that is used for nutrient transportation, but it is also the location of a response that defends against various stresses, named phloem-based defense (PBD). Phloem proteins (PP2s) are among the predominant proteins in phloem, indicating their potential functional role in PBD. Sclerotinia disease (SD), which is caused by the necrotrophic fungal pathogen S. sclerotiorum (Sclerotinia sclerotiorum), is a devastating disease that affects oil crops, especially Brassica napus (B. napus), mainly by blocking nutrition and water transportation through xylem and phloem. Presently, the role of PP2s in SD resistance is still largely estimated. Therefore, in this study, we identified 62 members of the PP2 gene family in the B. napus genome with an uneven distribution across the 19 chromosomes. A phylogenetic analysis classified the BnPP2s into four clusters (I–IV), with cluster I containing the most members (28 genes) as a consequence of its frequent genome segmental duplication. A comparison of the gene structures and conserved motifs suggested that BnPP2 genes were well conserved in clusters II to IV, but were variable in cluster I. Interestingly, the motifs in different clusters displayed unique features, such as motif 6 specifically existing in cluster III and motif 1 being excluded from cluster IV. These results indicated the possible functional specification of BnPP2s. A transcriptome data analysis showed that the genes in clusters II to IV exhibited dynamic expression alternation in tissues and the stimulation of S. sclerotiorum, suggesting that they could participate in SD resistance. A GWAS analysis of a rapeseed population comprising 324 accessions identified four BnPP2 genes that were potentially responsible for SD resistance and a transgenic study that was conducted by transiently expressing BnPP2-6 in tobacco (Nicotiana tabacum) leaves validated their positive role in regulating SD resistance in terms of reduced lesion size after inoculation with S. sclerotiorum hyphal plugs. This study provides useful information on PP2 gene functions in B. napus and could aid elaborated functional studies on the PP2 gene family. Full article

Odorant-binding proteins (OBPs) typically act as transporters of odor molecules and play an important role in insect host location. Here, we identified an OBP in brown planthopper (BPH) Nilaparvata lugens salivary glands via transcriptome sequencing. Real-time quantitative PCR and Western blotting analysis results showed that NlugOBP11 was highly expressed in salivary glands and secreted into rice plant during feeding, suggesting that it assists in BPH feeding on rice. Functional analysis in N. lugens saliva revealed that silencing this gene by RNA interference decreased the BPH stylet performance in the phloem of rice plants, reduced sap sucking, and ultimately led to insect death. Moreover, overexpression of NlugOBP11 in rice protoplasts or Nicotiana benthamiana leaves inhibited the production of defense-related signaling molecule salicylic acid in rice plant. The results demonstrate that NlugOBP11 is not only essential for BPH feeding, but also acts as an effector that inhibits plant defense. Full article

Vascular bundles play important roles in transporting nutrients, growth signals, amino acids, and proteins between aerial and underground tissues. In order to understand these sophisticated processes, a comprehensive analysis of the roles of the components located in the vascular tissues is required. A great deal of data has been obtained from proteomic analyses of vascular tissues in plants, which mainly aim to identify the proteins moving through the vascular tissues. Here, different aspects of the phloem and xylem proteins are reviewed, including their collection methods, and their main biological roles in growth, and biotic and abiotic stress responses. The study of vascular proteomics shows great potential to contribute to our understanding of the biological mechanisms related to development and defense in plants. Full article

To understand the positional and temporal defense mechanisms of coniferous tree bark at the tissue and cellular levels, the phloem topochemistry and structural properties were examined after artificially induced bark defense reactions. Wounding and fungal inoculation with Endoconidiophora polonica of spruce bark were carried out, and phloem tissues were frequently collected to follow the temporal and spatial progress of chemical and structural responses. The changes in (+)-catechin, (−)-epicatechin, stilbene glucoside, and resin acid distribution, and accumulation patterns within the phloem, were mapped using time-of-flight secondary ion mass spectrometry (cryo-ToF-SIMS), alongside detailed structural (LM, TEM, SEM) and quantitative chemical microanalyses of the tissues. Our results show that axial phloem parenchyma cells of Norway spruce contain (+)-catechins, the amount of which locally increases in response to fungal inoculation. The preformed, constitutive distribution and accumulation patterns of (+)-catechins closely follow those of stilbene glucosides. Phloem phenolics are not translocated but form a layered defense barrier with oleoresin compounds in response to pathogen attack. Our results suggest that axial phloem parenchyma cells are the primary location for (+)-catechin storage and synthesis in Norway spruce phloem. Chemical mapping of bark defensive metabolites by cryo-ToF-SIMS, in addition to structural and chemical microanalyses of the defense reactions, can provide novel information on the local amplitudes and localizations of chemical and structural defense mechanisms and pathogen–host interactions of trees. Full article

Lipid transfer proteins (LTPs) are a class of small, cationic proteins that bind and transfer lipids and play an important role in plant defense. However, their precise biological role in plants under adverse conditions including salinity and possible regulation by stress hormone abscisic acid (ABA) remains unknown. In this work, we studied the localization of LTPs and ABA in the roots of pea plants using specific antibodies. Presence of LTPs was detected on the periphery of the cells mainly located in the phloem. Mild salt stress (50 mM NaCI) led to slowing plant growth and higher immunostaining for LTPs in the phloem. The deposition of suberin in Casparian bands located in the endoderma revealed with Sudan III was shown to be more intensive under salt stress and coincided with the increased LTP staining. All obtained data suggest possible functions of LTPs in pea roots. We assume that these proteins can participate in stress-induced pea root suberization or in transport of phloem lipid molecules. Salt stress increased ABA immunostaining in pea root cells but its localization was different from that of the LTPs. Thus, we failed to confirm the hypothesis regarding the direct influence of ABA on the level of LTPs in the salt-stressed root cells. Full article