Host Plant Factors Research Articles

Knockout of the tomato translational elongation factor using CRISPR-Cas9 technology

Pathogenic viruses cause severe tomato losses around the world despite the development of both classical breeding and biotechnological methods. Since replication of phytoviruses involves the interaction between viral components and host plant factors, therefore loss-of-function mutations in the latters can confer viral resistance in plants. There are evidences that eukaryotic translation elongation factor 1 (eEF1) proteins are involved in the replication of some plant viruses. However, the involvement of individual subunits of the eEF1B in the viral cycle is still poorly understood.
 This work is devoted to the study of the role of the eEF1B factor in the development of tomato virus infection. The contribution of each of the α, β and γ subunits of the eEF1B factor to tomato viral resistance will be determined by CRISPR-Cas9-induced targeted mutagenesis of corresponding gene sequences. As an applied aspect, we expect to find ways to create tomato plants with increased resistance to certain viral diseases. A series of binary vectors contained sequences encoded different RNAs targeting the eEF1B subunit genes was constructed. As a result of Agrobacterium-mediated transformation of tomato, more than 300 independent transgenic lines were obtained. The presence of expression cassettes with functional genes (Cas9 and sgRNAs) was confirmed by PCR. The presence of mutations in target sequences was detected using T7E1 analysis and sequencing. It turned out that the majority of transgenic lines carrying mutations have a chimeric genotype, and mutations of the target genes in the homozygous state were not detected. The propagation of self-pollinated transgenic plants under greenhouse condition and following analyses of target genes to segregate the insertion of foreign DNA and obtain homozygous mutations in eEF1B subunit sequences are in progress.

Diversity and biogeography of plant phyllosphere bacteria are governed by latitude-dependent mechanisms.

Predicting and managing the structure and function of plant microbiomes requires quantitative understanding of community assembly and predictive models of spatial distributions at broad geographic scales. Here, we quantified the relative contribution of abiotic and biotic factors to the assembly of phyllosphere bacterial communities, and developed spatial distribution models for keystone bacterial taxa along a latitudinal gradient, by analyzing 16S rRNA gene sequences from 1453 leaf samples taken from 329 plant species in China. We demonstrated a latitudinal gradient in phyllosphere bacterial diversity and community composition, which was mostly explained by climate and host plant factors. We found that host-related factors were increasingly important in explaining bacterial assembly at higher latitudes while nonhost factors including abiotic environments, spatial proximity and plant neighbors were more important at lower latitudes. We further showed that local plant-bacteria associations were interconnected by hub bacteria taxa to form metacommunity-level networks, and the spatial distribution of these hub taxa was controlled by hosts and spatial factors with varying importance across latitudes. For the first time, we documented a latitude-dependent importance in the driving factors of phyllosphere bacteria assembly and distribution, serving as a baseline for predicting future changes in plant phyllosphere microbiomes under global change and human activities.

Deep spatial and temporal graph convolutional network for rice planthopper population dynamic forecasting

Rice planthoppers (RPH) are important pests that cause severe yield losses in rice production in China. The widespread and intensive use of insecticides to prevent RPH causes serious issues. Forecasting the population dynamics of RPH is an important part of integrated pest management, which helps to prevent impending RPH outbreaks and reduce the use of insecticide. However, forecasting RPH population dynamics is very challenging as it results from complex spatial and temporal dispersion processes impacted by many factors, such as source populations, meteorological conditions, and host plant characteristics. Therefore, a novel deep learning-based model using graph convolutional network (GCN) and long short-term memory network (LSTM) is proposed in this study to capture RPH population dynamics. This model includes one dynamic GCN (DGCN) for modeling source populations and two attention-based LSTM encoder-decoder network (ALSTM) for modeling meteorological and host plants, respectively. The proposed model can dynamically aggregate the outputs of one DGCN and two ALSTM based on data to produce the final output for each county. The proposed model is evaluated on the dataset collected in South and Southwest China during 2000–2019, which includes populations, meteorological and host plant factors. The results demonstrate that DGCN-ALSTM outperforms other state-of-art deep learning methods and traditional time series forecasting approaches. The improvement brought by DGCN-ALSTM are about 1.95 %, 1.32 %, and 1.60 % for brown planthopper population, and 1.79 %, 0.71 %, and 0.32 % for white back planthopper population according to the R, RMAE, and RRMSE take DGCN as the baseline, respectively. The proposed DGCN-ALSTM provides a new better tool to forecast RPH population dynamics and the accurate forecasting results can guide local plant protection organizations to develop detailed sustainable pest control strategies and methods to control RPH in time.

Risk Assessment of the Worldwide Expansion and Outbreak of Massicus raddei (Blessig) (Coleoptera: Cerambycidae) Based on Host Plant and Climatic Factors

Massicus raddei (Blessig) is a serious trunk borer of oak species, currently widespread only in eastern Asia. A better understanding of the invasive potential of this borer across other distribution-free areas is further needed to prevent its invasion and outbreaks. In this study, we mapped the current distribution of M. raddei, two susceptible hosts (Quercus mongolia and Q. liaotungensis) and all 11 host species of this borer, and then modeled their potential distributions. We comprehensively compared the current distributions and potential invasion ranges among M. raddei, susceptible hosts and all hosts to select areas at risk for the establishment of this borer. MaxEnt model predictions revealed that (1) the central and eastern US, a small area of central and western Europe, western Georgia, and central Argentina had suitable climates for M. raddei. Such highly suitable areas for this borer overlapped considerably with the current plantation and potential distributions of its hosts. Consequently, susceptible hosts and climate suitability together create the highest risk for M. raddei establishment and outbreaks, throughout central and eastern America, a small area of central Europe, western Norway and western Georgia, and (2) the broad host suitability across six continents creates a situation favorable for the colonization of this borer, further extending the spatial scale of possible infestation by M. raddei worldwide.

Diversity of Arbuscular Mycorrhizal Fungi (AMF) in Rhizosphere of Some Economic and Medicinal Crops in SEAMEO BIOTROP, Bogor, West Java

The diversity of terrestrial plants in Indonesia are very huge, including production crops such as palm oil (Elaeis sp.), teak (Tectona grandis L.), lemon (Citrus limon L.) and Aloe vera. The quality of production crops is influenced by the diversity of soil microorganisms, namely the Arbuscular Mycorrhizal Fungi (AMF). AMF plays an important role in the growth and development of the host plant. This study aims to determine the diversity of AMF in the rhizosphere of some production crops at SEAMEO BIOTROP, West Java. Research methods are soil sampling and preparation, soil sieving, AMF spore extraction and morphological identification. As a result, spore density tends to be uniform in all four plants (3 spores per 10 gram). The highest to lowest relative abundance percentage of spores on Glomus sp. (52.17%), Acaulospora sp. (34.79%) and Gigaspora sp. (13,04%). Soil, host plant and AMF factors affect the diversity of AMF.

Impact of Temperature and Rainfall Change on Epidemics Caused by Plant Viruses: A Review

Plant virus diseases are one of the limiting factors to crop productivity by diminishing the quantity, quality and responsible for significant economic losses worldwide. The Epidemic of plant virus diseases is the result of interactions between virus, host plant, vector, and environmental factors. Changes in host plants and insect vector dynamics that result from temperature and rainfall change could have an influence on the spread of plant viruses. The rising of temperature and heat stress increase the susceptibility of host plants to virus infection and accelerates the fitness of viruses to cause disease. The increasing temperature also changes insect vector population dynamics by accelerating insect phenology, causing earlier and prolonged colonization because it makes appropriate environmental conditions for the insect vectors. Insect populations of most virus vectors build up more rapidly in areas with high temperatures and high relative humidity and decline at low temperature. In addition, the rising temperatures can increase the efficiency of virus transmission from infected to healthy plants by insect vectors. An increasing frequency of heavy rainfall events is likely to slow the virus prevalence and incidence by washing insect vectors, thus reducing vector density. Flooding within annual crop growing period enhances the subsequent growth of weed and volunteer crop plant which act as reservoirs of insect vectors and the viruses, and its occurrence outside growing seasons increases subsequent growth of such reservoirs. Keywords : Host plant; Vectors; Virus epidemics DOI: 10.7176/JEES/12-1-01 Publication date: January 31 st 2022

Impact of Temperature and Rainfall Change on Epidemics caused by Plant viruses

Plant virus diseases are one of the limiting factors to crop productivity by diminishing the quantity, quality and responsible for significant economic losses worldwide. The Epidemic of plant virus diseases is the result of interactions between virus, host plant, vector, and environmental factors. Changes in host plants and insect vector dynamics that result from temperature and rainfall change could have an influence on the spread of plant viruses. The rising of temperature and heat stress increase the susceptibility of host plants to virus infection and accelerates the fitness of viruses to cause disease. The increasing temperature also changes insect vector population dynamics by accelerating insect phenology, causing earlier and prolonged colonization because it makes appropriate environmental conditions for the insect vectors. Insect populations of most virus vectors build up more rapidly in areas with high temperatures and high relative humidity and decline at low temperature. In addition, the rising temperatures can increase the efficiency of virus transmission from infected to healthy plants by insect vectors. An increasing frequency of heavy rainfall events is likely to slow the virus prevalence and incidence by washing insect vectors, thus reducing vector density. Flooding within annual crop growing period enhances the subsequent growth of weed and volunteer crop plant which act as reservoirs of insect vectors and the viruses, and its occurrence outside growing seasons increases subsequent growth of such reservoirs. Keywords: Host plant; Vectors; Virus epidemics DOI: 10.7176/JNSR/12-3-05 Publication date: February 28 th 2021

DIVERSITY OF FRUIT FLIES (TEPHRITIDAE: BACTROCERA SPP.) IN CAMPUS C OF AIRLANGGA UNIVERSITY, SURABAYA, INDONESIA

This research aims to get information about the species of host plants and fruit flies, composition and structure of community, distribution pattern, and impact of environmental factors to fruit flies in Campus C, Airlangga University. Research was conducted from August to November 2019. A modification of Steiner trap with methyl eugenol 1.5 ml bait was installed in nine sites. Each Steiner trap was placed on a mango tree 1-2 meters above ground level. Trapped fruit fly specimens were collected after one week. Four replications were made, with intervals between two periods of installation. As many as 682 host plants of the fruit flies were found at the study site consisting of 25 species from 15 families. Results showed that 1121 individuals of Bactrocera fruit flies were found, consisting of 6 species, namely B. carambolae, B. dorsalis, B. minuscula, B. papayae, B. occipitalis, and B. musae. The most abundant species was B. carambolae (62.8%), followed by B. dorsalis (22.8%), B. minuscula (8.4%), B. papayae (4.5%), B. occipitalis (1%), and the lowest was B. musae (0.5%). B. occipitalis has an even distribution pattern, while five other species have aggregated distribution patterns. The diversity index at nine locations ranged from 0.855 (low) to 1.328 (moderate). B. carambolae and B. dorsalis were the dominant species. The presence of fruit flies was influenced by environmental (humidity, temperature, sunlight intensity, wind) and host plant factors.

Recessive resistance to plant viruses by the deficiency of eukaryotic translation initiation factor genes.

Plant viruses, obligate parasitic pathogens, utilize a variety of host plant factors in the process of their infection due to the limited number of genes encoded in their own genomes. The genes encoding these host factors are called susceptibility genes because they are responsible for the susceptibility of plants to viruses. Plants lacking or having mutations in a susceptibility gene essential for the infection of a virus acquire resistance to the virus. Such resistance trait is called recessive resistance because of the recessive inherited characteristics. Recessive resistance is reported to account for about half of the plant viral resistance loci mapped in known cultivated crops. Eukaryotic translation initiation factor (eIF) 4E family genes are well-known susceptibility genes. Although there are many reports about eIF4E-mediated recessive resistance to plant viruses, the mechanistic insight of the resistance is still limited. Here we review focusing on studies that have elucidated the mechanism of eIF4E-mediated recessive resistance.

Edaphic and host plant factors are linked to the composition of arbuscular mycorrhizal fungal communities in the root zone of endangered Ulmus chenmoui Cheng in China.

Despite the importance of arbuscular mycorrhizal fungi (AMF) within deciduous forest ecosystems, we know little about how natural AMF communities are structured in the root zone of the endangered elm species Ulmus chenmoui. In this study, three U. chenmoui sampling sites, differing with respect to plant health, age, and growth status, were selected in Anhui Province, China. AMF biodiversity in the root zones of individual U. chenmoui trees was investigated using high‐throughput sequencing. In total, 61 AMF operational taxonomic units were detected. Five genera, namely Glomus (62.82%), Paraglomus (17.82%), Rhizophagus (4.29%), Septoglomus (4.06%) and Funneliformis (2.35%), and 29 species of AMF were identified. Correlation analysis indicated that available soil phosphorus and potassium concentrations were the main edaphic factors influencing AMF community structure. There was a difference in AMF species richness among the three U. chenmoui stands. Our study showed that soil nutrient concentrations and plant health, age, and growth status can exert a selective effect on the composition of the AMF population in the soil in the root zones of U. chenmoui trees.

A random survival forest illustrates the importance of natural enemies compared to host plant quality on leaf beetle survival rates

BackgroundWetlands are habitats where variation in soil moisture content and associated environmental conditions can strongly affect the survival of herbivorous insects by changing host plant quality and natural enemy densities. In this study, we combined natural enemy exclusion experiments with random survival forest analyses to study the importance of local variation in host plant quality and predation by natural enemies on the egg and larval survival of the leaf beetle Galerucella sagittariae along a soil moisture gradient.ResultsOur results showed that the exclusion of natural enemies substantially increased the survival probability of G. sagittariae eggs and larvae. Interestingly, the egg survival probability decreased with soil moisture content, while the larval survival probability instead increased with soil moisture content. For both the egg and larval survival, we found that host plant height, the number of eggs or larvae, and vegetation height explained more of the variation than the soil moisture gradient by itself. Moreover, host plant quality related variables, such as leaf nitrogen, carbon and phosphorus content did not influence the survival of G. sagittariae eggs and larvae.ConclusionOur results suggest that the soil moisture content is not an overarching factor that determines the interplay between factors related to host plant quality and factors relating to natural enemies on the survival of G. sagittariae in different microhabitats. Moreover, the natural enemy exclusion experiments and the random survival forest analysis suggest that natural enemies have a stronger indirect impact on the survival of G. sagittariae offspring than host plant quality.

VirD5 is required for efficient Agrobacterium infection and interacts with Arabidopsis VIP2.

During Agrobacterium (Agrobacterium tumefaciens) infection, the translocated virulence proteins (VirD2, VirE2, VirE3, VirF and VirD5) play crucial roles. It is thought that, through protein-protein interactions, Agrobacterium uses and abuses host plant factors and systems to facilitate its infection. Although some molecular functions have been revealed, the roles of VirD5 still need to be further elucidated. Here, plant transformation and tumorigenesis mediated by genetically modified Agrobacterium strains were performed to examine VirD5 roles. In addition, protein-protein interaction-associated molecular and biochemistry technologies were used to reveal and elucidate VirD5 interaction with Arabidopsis VirE2 interacting protein 2 (VIP2). Our results showed that deleting virD5 from Agrobacterium reduced its tumor formation ability and stable transformation efficiency but did not affect the transient transformation efficiency. We also found that VirD5 can interact with Arabidopsis VIP2. Further experiments demonstrated that VirD5 can affect VIP2 binding to cap-binding proteins (CBP20 and CBP80). The tumorigenesis efficiency for cbp80 mutant was not significantly changed, but that for cbp20, cbp20cbp80 mutants were significantly increased. This work demonstrates experimentally that VirD5 is required for efficient Agrobacterium infection and may promote this process by competitive interaction with Arabidopsis VIP2. CBP20 is involved in the Agrobacterium infection process and its effect can be synergistically enhanced by CBP80.

Population and Diversity of Arbuscular Mycorrhiza Fungi in the Rhizosphere of Kasetsart Cassava Clone Grown on Two Different Locations

Population and diversity of arbuscular mycorrhiza fungi (AMF) are varied in the soil and influenced by biotic factors such as host plant and abiotic factors such as soil fertility, soil moisture, pH, temperature, etc. This study aimed to determine the population, diversity, and the dominant type of AMF in the rhizosphere of Kasetsart cassava clones obtained from LampungTimur and Tulang Bawang Barat Regencies, Lampung Province, Indonesia. Population of AMF was counted directly from the rhizosphere of Kasetsart cassava clones and the diversity of AMF was assesed using a pot culture experiment. The results showed that the population and the diversity of AMF in the rhizosphere of Kasetsart clone obtained from Tulang Bawang Barat was higher than that from LampungTimur. The predominant type of AMF found in the pot culture using soil samples from Lampung Timur was spore with S2 code that belongs to the genus Gigaspora and S4 code that belongs to the genus Glomus. On the other hand, the type of AMF found in the rhizosphere of soil samples from Tulang Bawang Barat was dominated by spore with S9 code that belongs to the genus Entrophospora.

Effects of Host Plant Factors on the Bacterial Communities Associated with Two Whitefly Sibling Species.

BackgroundAlthough discrepancy in the specific traits and ecological characteristics of Bemisia tabaci between species are partially attributed to the B. tabaci-associated bacteria, the factors that affect the diversity of B. tabaci-associated bacteria are not well-understood. We used the metagenomic approach to characterize the B. tabaci-associated bacterial community because the approach is an effective tool to identify the bacteria.Methodology and ResultsTo investigate the effects of the host plant and a virus, tomato yellow leaf curl virus (TYLCV), on the bacterial communities of B. tabaci sibling species B and Q, we analyzed the bacterial communities associated with whitefly B and Q collected from healthy cotton, healthy tomato, and TYLCV-infected tomato. The analysis used miseq-based sequencing of a variable region of the bacterial 16S rDNA gene. For the bacteria associated with B. tabaci, we found that the influence of the host plant species was greater than that of the whitefly cryptic species. With further analysis of host plants infected with the TYLCV, the virus had no significant effects on the B. tabaci-associated bacterial community.ConclusionsThe effects of different plant hosts and TYLCV-infection on the diversity of B. tabaci-associated bacterial communities were successfully analyzed in this study. To explain why B. tabaci sibling species with different host ranges differ in performance, the analysis of the bacterial community may be essential to the explanation.

In silico prediction and validation of potential gene targets for pospiviroid-derived small RNAs during tomato infection

Viroids are small, covalently closed, circular non-coding RNA pathogens of flowering plants. It is proposed that the symptoms of viroid pathogenesis result from a direct interaction between the viroid genomic RNA and unknown host plant factors. Using a comparative genomic approach we took advantage of the detailed annotation of the Arabidopsis thaliana (Arabidopsis) genome to identify sequence homologies between putative viroid-derived small RNAs (vd-sRNAs) and coding regions in the plant genome. A pool of sequence homologies among 29 species of the Pospiviroidae family and the Arabidopsis genome was analyzed. Using this strategy we identified putative host gene targets that may be involved in symptom expression in viroid-infected plants. In this communication, we report the in silico prediction and the experimental validation of pospiviroid-derived sRNAs conserved in the lower strand of the pathogenicity domain of seven viroid species infecting tomato; those vd-sRNAs targeted for cleavage the host mRNA encoding a conserved tomato WD40-repeat protein (SolWD40-repeat; SGN_U563134). Analysis of SolWD40-repeat expression indicated that this gene is down-regulated in tomato plants infected with tomato planta macho viroid (TPMVd). Furthermore, 5′ RLM-RACE revealed that the SolWD40-repeat mRNA is cleaved at the predicted target site showing complementarity to a corresponding TPMVd-sRNA identified in silico. Our approach proved to be useful for the identification of natural host genes containing sequence homologies with segments of the Pospiviroidae genome. Using this strategy we identified a functionally conserved gene in Arabidopsis and tomato, whose expression was modified during viroid infection in the host genome; regulation of this gene expression could be guided by vd-sRNA:mRNA complementarity, suggesting that the comparison of the Arabidopsis genome to viroid sequences could lead to the identification of unexpected interactions between viroid RNAs and their host.

Rad54 is not essential for any geminiviral replication mode in planta.

The circular single-stranded DNA of phytopathogenic geminiviruses is propagated by three modes: complementary strand replication (CSR), rolling circle replication (RCR) and recombination-dependent replication (RDR), which need host plant factors to be carried out. In addition to necessary host polymerases, proteins of the homologous recombination repair pathway may be considered essential, since geminiviruses are particularly prone to recombination. Among several others, Rad54 was suggested to be necessary for the RCR of Mungbean yellow mosaic India virus. This enzyme is a double-stranded DNA-dependent ATPase and chromatin remodeller and was found to bind and modulate the viral replication-initiator protein in vitro and in Saccharomyces cerevisiae. In contrast to the previous report, we scrutinized the requirement of Rad54 in planta for two distinct fully infectious geminiviruses with respect to the three replication modes. Euphorbia yellow mosaic virus and Cleome leaf crumple virus were inoculated into Rad54-deficient and wildtype Arabidopsis thaliana plant lines to compare the occurrence of viral DNA forms. Replication intermediates were displayed in the time course of infection by one and two-dimensional agarose gel electrophoresis and Southern hybridization. The experiments showed that Rad54 was neither essential for CSR, RCR nor RDR, and it had no significant influence on virus titers during systemic infection.

The putative Agrobacterium transcriptional activator-like virulence protein VirD5 may target T-complex to prevent the degradation of coat proteins in the plant cell nucleus.

Agrobacterium exports at least five virulence proteins (VirE2, VirE3, VirF, VirD2, VirD5) into host cells and hijacks some host plant factors to facilitate its transformation process. Random DNA binding selection assays (RDSAs), electrophoretic mobility shift assays (EMSAs) and yeast one-hybrid systems were used to identify protein-bound DNA elements. Bimolecular fluorescence complementation, glutathione S-transferase pull-down and yeast two-hybrid assays were used to detect protein interactions. Protoplast transformation, coprecipitation, competitive binding and cell-free degradation assays were used to analyze the relationships among proteins. We found that Agrobacterium VirD5 exhibits transcriptional activation activity in yeast, is located in the plant cell nucleus, and forms homodimers. A specific VirD5-bound DNA element designated D5RE (VirD5 response element) was identified. VirD5 interacted directly with Arabidopsis VirE2 Interacting Protein 1 (AtVIP1). However, the ternary complex of VirD5-AtVIP1-VirE2 could be detected, whereas that of VirD5-AtVIP1-VBF (AtVIP1 Binding F-box protein) could not. We demonstrated that VirD5 competes with VBF for binding to AtVIP1 and stabilizes AtVIP1 and VirE2 in the cell-free degradation system. Our results indicated that VirD5 may act as both a transcriptional activator-like effector to regulate host gene expression and a protector preventing the coat proteins of the T-complex from being quickly degraded by the host's ubiquitin proteasome system (UPS).

Host Tree Influences on Longicorn Beetle (Coleoptera: Cerambycidae) Attack in SubtropicalCorymbia(Myrtales: Myrtaceae)

Phoracantha longicorn beetles are endemic to Australia, and some species have become significant pests of eucalypts worldwide, yet little is known about their host plant interactions and factors influencing tree susceptibility in Australia. Here, we investigate the host relationships of Phoracantha solida (Blackburn, 1894) on four eucalypt taxa (one pure species and three hybrid families), examining feeding site physical characteristics including phloem thickness, density, and moisture content, and host tree factors such as diameter, height, growth, taper, and survival. We also determine the cardinal and vertical (within-tree) and horizontal (between-tree) spatial distribution of borers. Fewer than 10% of P. solida attacks were recorded from the pure species (Corymbia citriodora subsp. variegate (Hook)), and this taxon also showed the highest survival, phloem thickness, relative growth rate, and bark:wood area. For the two most susceptible taxa, borer severity was negatively correlated with moisture content, and positively related to phloem density. Borers were nonrandomly and nonuniformly distributed within trees, and were statistically aggregated in 32% of plots. More attacks were situated on the northern side of the tree than the other aspects, and most larvae fed within the lower 50 cm of the bole, with attack height positively correlated with severity. Trees with borers had more dead neighbors, and more bored neighbors, than trees without borers, while within plots, borer incidence and severity were positively correlated. Because the more susceptible taxa overlapped with less susceptible taxa for several physical tree factors, the role of primary and secondary chemistries in determining host suitability needs to be investigated. Nevertheless, taxon, moisture content, phloem density, tree size, and mortality of neighboring trees appeared the most important physical characteristics influencing host suitability for P. solida at this site.

A Paradigm for Endosymbiotic Life: Cell Differentiation of Rhizobium Bacteria Provoked by Host Plant Factors

Symbiosis between Rhizobium bacteria and legumes leads to the formation of the root nodule. The endosymbiotic bacteria reside in polyploid host cells as membrane-surrounded vesicles where they reduce atmospheric nitrogen to support plant growth by supplying ammonia in exchange for carbon sources and energy. The morphology and physiology of endosymbionts, despite their common function, are highly divergent in different hosts. In galegoid plants, the endosymbionts are terminally differentiated, uncultivable polyploid cells, with remarkably elongated and even branched Y-shaped cells. Bacteroid differentiation is controlled by host peptides, many of which have antibacterial activity and require the bacterial function of BacA. Although the precise and combined action of several hundred host peptides and BacA has yet to be discovered, similarities, especially to certain insect-bacterium symbioses involving likewise host peptides for manipulation of endosymbionts, suggest convergent evolution. Rhizobium-legume symbiosis provides a rich source of information for understanding host-controlled endosymbiotic life in eukaryotic cells.

The roles of bacterial and host plant factors in Agrobacterium-mediated genetic transformation

The genetic transformation of plants mediated by Agrobacterium tumefaciens represents an essential tool for both fundamental and applied research in plant biology. For a successful infection, culminating in the integration of its transferred DNA (T-DNA) into the host genome, Agrobacterium relies on multiple interactions with host-plant factors. Extensive studies have unraveled many of such interactions at all major steps of the infection process: activation of the bacterial virulence genes, cell-cell contact and macromolecular translocation from Agrobacterium to host cell cytoplasm, intracellular transit of T-DNA and associated proteins (T-complex) to the host cell nucleus, disassembly of the T-complex, T-DNA integration, and expression of the transferred genes. During all these processes, Agrobacterium has evolved to control and even utilize several pathways of host-plant defense response. Studies of these Agrobacterium-host interactions substantially enhance our understanding of many fundamental cellular biological processes and allow improvements in the use of Agrobacterium as a gene transfer tool for biotechnology.