Reasserting the priority of <Emphasis Type="Italic">Hypericum cordiforme</Emphasis> A.St.-Hil. (Hypericaceae) over <Emphasis Type="Italic">H. cordatum</Emphasis> (Vell.) N.Robson

Priority concerning the publication of St. Hilaire’s name Hypericum cordiforme over H. cordatum is confirmed since its effective publication in Flora Brasiliae Meridionalis (1828) predates the publication of Vellozo’s name Receveura cordata, the basionym of H. cordatum, in Florae fluminensis (1829). We also provide a second-step lectotypification for H. cordiforme and a lectotypification and epitypification for Receveura cordata. Hypericum cordiforme var. genuinum is for the first time determined to be an invalid name, and H. cordatum subsp. kleinii is placed in the synonymy of H. cordiforme.     

Mid-Pliocene bald ibis (<Emphasis Type="Italic">Geronticus</Emphasis> cf. <Emphasis Type="Italic">calvus</Emphasis>; Aves: Threskiornithidae) from the Cradle of Humankind,Gauteng, South Africa and its environmental and evolutionary implications

We document the presence of the bald ibis genus Geronticus Wagler, 1832 (Aves: Threskiornithidae) from the mid-Pliocene (ca. 3–3.5 Ma) of South Africa based on an incomplete skull from the Bolt’s Farm Cave System (Cradle of Humankind, Gauteng, South Africa). The fossil cranium is distinct on morphometric and structural grounds from Geronticus apelex, the only other Pliocene Geronticus described from Southern Africa, but is very close in dimensions and general morphology to the extant G. calvus of South Africa, and the Bolt’s Farm fossil ibis is therefore attributed to G. cf. calvus. Modern Geronticus ibises are localised to temperate, open grasslands and semi-arid steppe, and nest exclusively on cliffs and similar rocky eminences. Given its attribution as G. cf. calvus, the Bolt’s Farm ibis was likely similar in ecology to the extant G. calvus, suggesting that the habitat surrounding the Bolt’s Farm fossil site during the mid-Pliocene featured open grassland and presence of cliffs. This record constrains the divergence between G. calvus and its putative ancestor G. apelex to the mid-Pliocene and implies that G. calvus has possibly been subject to “evolutionary/morphological stasis” for more than 3 million years. This postulated stasis would be consistent with the notion that extant genera with few species (i.e. high genus-to-species ratios) show low rates of phenotypic diversification and change through the Neogene.     

Vetch aphid, <Emphasis Type="Italic">Megoura crassicauda</Emphasis> (Hemiptera: Aphididae), parasitism does not reduce the bean production of narrow-leaved vetch, <Emphasis Type="Italic">Vicia sativa</Emphasis> subsp. <Emphasis Type="Italic">nigra</Emphasis> (Fabaceae)

Megoura crassicauda Mordvilko (Hemiptera: Aphididae) is a dominant aphid species found on Vicia sativa subsp. nigra (L.) Ehrh. (Fabaceae) in the spring. Worker ants of Formica japonica, the dominant ant species attracted to the extrafloral nectaries of V. s. nigra, often attack ladybirds (Coccinella septempunctata), which are aphid enemies. However, the workers of F. japonica do not attack or exclude M. crassicauda, the non-myrmecophilous aphid. It appears that the “bodyguard” retained by the plant guards the plant’s herbivore by attacking the herbivores’ enemies, rather than guarding the plant itself. The relationship between V. s. nigra and M. crassicauda was observed in the field to examine and evaluate the cost of parasitism. Parasitism by M. crassicauda delayed flower bud formation markedly in V. s. nigra but did not kill the plants. V. s. nigra plants that were parasitized showed a net bean production similar to that of the non-parasitized controls. The parasitism rate of M. crassicauda increased when extrafloral nectaries were used by F. japonica. These results may indicate that M. crassicauda provides V. s. nigra with benefits by preventing other serious disadvantages.     

Susceptibility of germinating cruciferous seeds to <Emphasis Type="Italic">Bagrada hilaris</Emphasis> (Hemiptera: Pentatomidae) feeding injury

Bagrada hilaris (Burmeister) (Hemiptera: Pentatomidae) is a serious pest that attacks both germinating and seedling stages of a variety of cruciferous crops grown in the Central Coast of California. B. hilaris feeding on germinating seeds can cause severe stunting and plant mortality, and little is known about the feeding preference of B. hilaris for germinating seeds of major cruciferous hosts and varieties of hosts. No-choice and choice experiments were conducted in which germinating seeds in soilless and soil settings were exposed to B. hilaris adults for 7 days. Susceptibility scores were developed using B. hilaris feeding injury sites, distorted leaves, and deformed and dead plants to determine the overall B. hilaris preference for germinating host seeds. Based on the scores, the order of preference was arugula (Eruca sativa L.)?>?turnip (B. rapa L. var. rapa)?>?mizuna (B. rapa L. nipposinica)?>?kale (B. oleracea L. acephala)?>?choi (Brassica rapa L. var. chinensis)?>?broccoli (B. oleracea var. italica Plenck)?>?cauliflower (B. oleracea L. var. botrytis)?>?lettuce (Lactuca sativa L.)?>?sweet alyssum (Lobularia maritima [L.] Desv.). The lowest feeding injury was recorded on germinating lettuce and sweet alyssum seeds. Furthermore, no-choice and choice experiments were conducted with four varieties each of arugula and mizuna, twelve varieties each of kale and choi, and nine varieties/types of leafy Asian greens. The arugula varieties ‘Wild Rocket’ and ‘Spirit’ were more damaged by B. hilaris than other varieties tested. Among mizuna varieties, ‘Beira F1’ was more attractive to B. hilaris than ‘Scarlet’ or ‘Starbor F1.’ The choi varieties ‘Tokyo Bekana,’ ‘Feng Qing Choi F1,’ ‘Joi Choi F1,’ and ‘Win-Win Choi F1’ were more attractive than ‘Rosie F1.’ The leafy Asian greens variety ‘Carlton F1’ was more attractive to B. hilaris than ‘Yukina Savon,’ ‘Tatsoi OG,’ ‘Komatsuna Summerfest F1,’ ‘Red Rain F1,’ and ‘Shungiku.’ Therefore, the results suggest that not all varieties were equally susceptible to B. hilaris feeding and possibly be utilized for further field evaluation as a trap crop or developing more resistant varieties to B. hilaris.     

Association between <Emphasis Type="Italic">ATM</Emphasis> gene polymorphisms,lung cancer susceptibility and radiation-induced pneumonitis: a meta-analysis

Background

Previous studies have suggested that DNA double-strand break (DSB) repair is an important protective pathway after damage. The ataxia telangiectasia mutated (ATM) gene plays an important role in the DNA DSB repair pathway. DNA damage is a major cytotoxic effect that can be caused by radiation, and the ability to repair DNA after damage varies among different tissues. Impaired DNA repair pathways are associated with high sensitivity to radiation exposure. Hence, ATM gene polymorphisms are thought to influence the risk of cancer and radiation-induced pneumonitis (RP) risk in cancer patients treated with radiotherapy. However, the results of previous studies are inconsistent. We therefore conducted this comprehensive meta-analysis.

Methods

A systematic literature search was performed in the PubMed, Embase, China National Knowledge Internet (CNKI) and Wanfang databases to identify studies that investigated the association between the ATM gene polymorphisms and both lung cancer and RP radiotherapy-treated lung cancer (the last search was conducted on Dec.10, 2015). The odds ratio (OR) and 95% confidence interval (CI) were used to investigate the strength of these relationships. Funnel plots and Begg’s and Egger’s tests were conducted to assess the publication bias. All analyses were performed in STATA 13.0 software.

Results

Ten eligible case-control studies (4731 cases and 5142 controls) on lung cancer susceptibility and four (192 cases and 772 controls) on RP risk were included. The results of the overall and subgroup analyses indicated that in the ATM gene, the rs189037 (?111G?>?A, ?4519G?>?A), rs664677 (44831C?>?T, 49238C?>?T) and rs664143 (131,717 T?>?G) polymorphisms were significantly associated with lung cancer susceptibility (OR?=?1.21, 95% CI?=?1.04–1.39, P?=?0.01; OR?=?1.26, 95% CI?=?1.06–1.49, P?=?0.01; OR?=?1.43, 95% CI?=?1.15–1.78, P?<?0.01). Additionally, the rs189037 variant was significantly associated with RP risk (OR?=?1.74, 95% CI?=?1.02–2.97, P?=?0.04). No publication bias was found in the funnel plots, Begg’s tests or Egger’s tests.

Conclusions

The results indicate that the ATM rs189037, rs664677 and rs664143 gene polymorphisms are risk factors for lung cancer, while the ATM rs189037 variant was significantly associated with RP risk.

     

Occurrence and distribution of multiple antibiotic-resistant <Emphasis Type="Italic">Enterococcus</Emphasis> and <Emphasis Type="Italic">Lactobacillus</Emphasis> spp. from Indian poultry: in vivo transferability of their erythromycin,tetracycline and vancomycin resistance

The objective of this study was to determine the occurrence and distribution of antibiotic resistant (AR) lactic acid bacteria (LAB) in Indian poultry. LAB from poultry farm feces (n = 21) and samples from slaughter houses comprising chicken intestine (n = 46), raw meat (n = 23), and sanitary water (n = 4) were evaluated and compared with those from organic chicken (OC) collected from nearby villages. Screening studies showed 5–7 log units higher erythromycin (ER), tetracycline (TC) and vancomycin (VAN) resistant LAB from conventional poultry chicken (CC) compared to OC. Molecular characterization of isolated cultures (n = 32) with repetitive-PCR profiling and 16S rRNA gene sequencing revealed their taxonomical status as Enterococcus faecium (n = 16), Enterococcus durans (n = 2), Lactobacillus plantarum (n = 10), Lactobacillus pentosus (n = 1) and Lactobacillus salivarius (n = 3). The isolates were found to harbor erm(B), msr(C), msr(A/B), tet(M), tet(L) and tet(K) genes associated with Tn916 and Tn917 family transposons. Expression studies through real-time PCR revealed antibiotic-induced expression of the identified AR genes. In vitro and in vivo conjugational studies revealed transfer of ER and TC resistant (ER^R and TC^R) genes with transfer frequencies of 10^?7 and 10^?4 transconjugants recipient^?1, respectively. Although no known VAN resistance (VAN^R) genes were detected, high phenotypic resistance was observed and was transferable to the recipient. From a public health point of view, this study reports Indian poultry as a major source of high levels of AR bacteria contaminating the food chain and the environment. Thus, urgent and determined strategies are needed to control the spread of multiple AR bacteria.     

Revision of <Emphasis Type="Italic">Neolebouria</Emphasis> Gibson, 1976 (Digenea: Opecoelidae), with <Emphasis Type="Italic">Trilobovarium</Emphasis> n. g., for species infecting tropical and subtropical shallow-water fishes

A new opecoelid trematode is reported from fishes of the Lethrinidae, Lutjanidae and Nemipteridae off Lizard Island on the northern Great Barrier Reef, Australia. The new species keys to Neolebouria Gibson, 1976 and shows strong similarity to several species of that genus, but is not consistent with the type-species, N. georgiensis Gibson, 1976, or others known from temperate/polar and/or deep-sea fishes. The new species is also phylogenetically distant from N. lanceolata (Price, 1934) Reimer, 1987, the only representative of the genus for which molecular data are available. A new genus, Trilobovarium n. g., is proposed for the new species, T. parvvatis n. sp. Eight morphologically similar species, previously recognised as belonging to Neolebouria, from shallow-water, mostly tropical/subtropical fishes, are transferred to Trilobovarium: T. diacopae (Nagaty & Abdel Aal, 1962) n. comb.; T. ira (Yamaguti, 1940) n. comb.; T. khalili (Ramadan, 1983) n. comb.; T. krusadaiense (Gupta, 1956) n. comb.; T. lineatum (Aken’Ova & Cribb, 2001) n. comb.; T. moretonense (Aken’Ova & Cribb, 2001) n. comb.; T. palauense (Machida, 2014) n. comb.; and T. truncatum (Linton, 1940) n. comb. Paramanteriella Li, Qiu & Zhang, 1988 is resurrected for five species of Neolebouria with a post-bifurcal genital pore: P. cantherini Li, Qiu & Zhang, 1988; P. capoori (Jaiswal, Upadhyay, Malhotra, Dronen & Malhotra, 2014) n. comb.; P. confusa (Overstreet, 1969) n. comb.; P. leiperi (Gupta, 1956) n. comb.; and P. pallenisca (Shipley & Hornell, 1905) n. comb. Neolebouria georgenascimentoi Bray, 2002, a species with an exceptionally long cirrus-sac, is transferred to Bentholebouria Andres, Pulis & Overstreet, 2004 as B. georgenascimentoi (Bray, 2002) n. comb., and N. maorum (Allison, 1966) Gibson 1976, an unusual species known from cephalopods, is designated a species incertae sedis. Eleven species are retained in a revised concept of Neolebouria.     

Phylogenetic relationships of the genus <Emphasis Type="Italic">Armadolepis</Emphasis> Spassky, 1954 (Eucestoda,Hymenolepididae), with descriptions of two new species from Palaearctic dormice (Rodentia,Gliridae)

Two new species of hymenolepidid cestodes belonging to the genus Armadolepis Spassky, 1954 are described from dormice (Gliridae) from the southern East European Plain and the northwestern Caucasus, Russia. Armadolepis (Bremserilepis) longisoma n. sp., with a rudimentary, unarmed rostellar apparatus is described from the fat dormouse Glis glis (Linnaeus) from the Republic of Adygeya, Russia. Additionally, A. (Armadolepis) dryomi n. sp., characterised by a well-developed rostellar apparatus and armed rhynchus is described from the forest dormouse Dryomys nitedula Pallas from Rostov Oblast’, Russia. Armadolepis (Bremserilepis) longisoma n. sp. differs from A. (Bremserilepis) myoxi (Rudolphi, 1819) in having a substantially longer strobila and cirrus-sac, wider scolex and ovary and larger rostellar pouch and testes. Armadolepis (Armadolepis) dryomi n. sp. is distinguishable from A. (Armadolepis) spasskii Tenora & Baru?, 1958, A. (Armadolepis) jeanbaeri Makarikov, 2017 and A. (Armadolepis) tenorai Makarikov, 2017 in having a substantially longer and wider strobila, and larger rostellar pouch and cirrus-sac. Furthermore, A. dryomi n. sp. can be distinguished from its congeners by the number and size of rostellar hooks and the arrangement of the testes. Phylogenetic affinities of Armadolepis were studied for the first time using partial sequences of the nuclear ribosomal 28S DNA gene. Phylogenetic analysis strongly supported the status of Armadolepis as a separate genus belonging to the “Rodentolepis clade”.     

Characterization of <Emphasis Type="Italic">Lr75</Emphasis>: a partial,broad-spectrum leaf rust resistance gene in wheat

Key message

Here, we describe a strategy to improve broad-spectrum leaf rust resistance by marker-assisted combination of two partial resistance genes. One of them represents a novel partial adult plant resistance gene, named Lr75.

Abstract

Leaf rust caused by the fungal pathogen Puccinia triticina is a damaging disease of wheat (Triticum aestivum L.). The combination of several, additively-acting partial disease resistance genes has been proposed as a suitable strategy to breed wheat cultivars with high levels of durable field resistance. The Swiss winter wheat cultivar ‘Forno’ continues to show near-immunity to leaf rust since its release in the 1980s. This resistance is conferred by the presence of at least six quantitative trait loci (QTL), one of which is associated with the morphological trait leaf tip necrosis. Here, we used a marker-informed strategy to introgress two ‘Forno’ QTLs into the leaf rust-susceptible Swiss winter wheat cultivar ‘Arina’. The resulting backcross line ‘ArinaLrFor’ showed markedly increased leaf rust resistance in multiple locations over several years. One of the introgressed QTLs, QLr.sfr-1BS, is located on chromosome 1BS. We developed chromosome 1B-specific microsatellite markers by exploiting the Illumina survey sequences of wheat cv. ‘Chinese Spring’ and mapped QLr.sfr-1BS to a 4.3 cM interval flanked by the SSR markers gwm604 and swm271. QLr.sfr-1BS does not share a genetic location with any of the described leaf rust resistance genes present on chromosome 1B. Therefore, QLr.sfr-1BS is novel and was designated as Lr75. We conclude that marker-assisted combination of partial resistance genes is a feasible strategy to increase broad-spectrum leaf rust resistance. The identification of Lr75 adds a novel and highly useful gene to the small set of known partial, adult plant leaf rust resistance genes.

     

Can a biologist fix a radio? — or,what I learned while studying apoptosis

This article by Yu. Lazebnik, “Can a Biologist Fix a Radio? — or, What I Learned while Studying Apoptosis” has already been published in English (Cancer Cell, 2002, 2, 179–182) and in Russian (Uspekhi Gerontologii, 2003, No. 12, 166–171). Nevertheless, we have undertaken its secondary publication in our journal for two reasons: first, our journal has different readers, and, second, the great significance of this manifest of Yuri Lazebnik. The author in bright and clever form shows the emerging necessity to create formalized language designed to describe complicated systems of regulation of biochemical processes in living cells. The article is published with permission of Cancer Cell and Uspekhi Gerontologii.Editor-in-Chief of Biokhimiya/Biochemistry (Moscow) V.P.Skulachev     

Heterologous expression of a novel <Emphasis Type="Italic">Poa pratensis</Emphasis> gibberellin 2-oxidase gene, <Emphasis Type="Italic">PpGA2ox</Emphasis>, caused dwarfism,late flowering,and increased chlorophyll accumulation in <Emphasis Type="Italic">Arabidopsis</Emphasis>

Gibberellin 2-oxidases (GA2oxs) irreversibly convert bioactive gibberellins (GAs) and their immediate precursors into inactive GAs via 2-β hydroxylation and so regulate gibberellin content in plants. However, to the best of our knowledge, little has been known about the GA2oxs and its function in cool season turfgrass Poa pratensis. In this study, rapid amplification of cDNA end (RACE) was employed to isolate PpGA2ox from P. pratensis. The open reading frame of PpGA2ox was 1 047 bp in length, corresponding to 348 amino acids. PpGA2ox was localized in both nucleus and cytoplasm. The expression of PpGA2ox could be up-regulated by 10 μM gibberellic acid, 5 μM methyl jasmonate, or 10 μM indole-3-acetic acid. In addition, its native promoter could drive GUS expression in both leaf apex and shoot apical region. Moreover, overexpression of PpGA2ox in Arabidopsis led to GA-deficiency leading to dwarf phenotype, delayed flowering time, and increased chlorophyll content. Our study suggests that PpGA2ox could be a candidate gene for breeding new cultivars of P. pratensis.     

Disentangling the effects of isolation-by-distance and isolation-by-environment on genetic differentiation among <Emphasis Type="Italic">Rhododendron</Emphasis> lineages in the subgenus <Emphasis Type="Italic">Tsutsusi</Emphasis>

Ecological speciation has long been noted as a central topic in the field of evolutionary biology, and investigation into the relative importance of ecological and geographical factors is becoming increasingly emphasized. We surveyed genetic variation of 277 samples from 25 populations of nine Rhododendron species within Tsutsusi subgenus in Taiwan using simple sequence repeats of expressed sequence tags. Bayesian clustering revealed four genetic lineages: (1) the Rhododendron simsii, Rhododendron kanehirai, and Rhododendron nakaharae lineage (lineage 1); (2) the Rhododendron longiperulatum, Rhododendron breviperulatum, and Rhododendron noriakianum lineage (lineage 2); (3) the Rhododendron rubropilosum lineage (lineage 3); and (4) the Rhododendron oldhamii lineage (lineage 4). Asymmetric introgressions were found from lineage 3 into lineages 1 and 2 (introgressed lineages). Genetic admixture of non-R. oldhamii species was also revealed by a neighbor-joining tree. Variation partitioning showed that environment explained much larger portions of genetic variation than geography between non-introgressed lineages (i.e., between R. oldhamii and other lineages). However, the Mantel and partial Mantel tests and the multiple matrix regression with randomization found that isolation-by-distance played a more important role than isolation-by-environment (IBE) in contributing to genetic variation in most between lineage comparisons. Nevertheless, strong IBE was found when compared between non-introgressed lineages of R. oldhamii and R. rubropilosum, suggesting post-speciation ecological divergence. Several environmental variables, including annual mean temperature, aspect, isothermality, seasonal precipitation, slope, and soil pH, could be important ecological drivers involved in reproductive isolation between R. oldhamii and non-R. oldhamii species within the Tsutsusi subgenus.     

<Emphasis Type="Italic">PAD4</Emphasis>, <Emphasis Type="Italic">LSD1</Emphasis> and <Emphasis Type="Italic">EDS1</Emphasis> regulate drought tolerance,plant biomass production,and cell wall properties

Key message

Arabidopsis and poplar with modified PAD4, LSD1 and EDS1 genes exhibit successful growth under drought stress. The acclimatory strategies depend on cell division/cell death control and altered cell wall composition.

Abstract

The increase of plant tolerance towards environmental stresses would open much opportunity for successful plant cultivation in these areas that were previously considered as ineligible, e.g. in areas with poor irrigation. In this study, we performed functional analysis of proteins encoded by PHYTOALEXIN DEFICIENT 4 (PAD4), LESION SIMULATING DISEASE 1 (LSD1) and ENHANCED DISEASE SUSCEPTIBILITY 1 (EDS1) genes to explain their role in drought tolerance and biomass production in two different species: Arabidopsis thaliana and Populus tremula × tremuloides. Arabidopsis mutants pad4-5, lsd1-1, eds1-1 and transgenic poplar lines PAD4-RNAi, LSD1-RNAi and ESD1-RNAi were examined in terms of different morphological and physiological parameters. Our experiments proved that Arabidopsis PAD4, LSD1 and EDS1 play an important role in survival under drought stress and regulate plant vegetative and generative growth. Biomass production and acclimatory strategies in poplar were also orchestrated via a genetic system of PAD4 and LSD1 which balanced the cell division and cell death processes. Furthermore, improved rate of cell division/cell differentiation and altered physical properties of poplar wood were the outcome of PAD4- and LSD1-dependent changes in cell wall structure and composition. Our results demonstrate that PAD4, LSD1 and EDS1 constitute a molecular hub, which integrates plant responses to water stress, vegetative biomass production and generative development. The applicable goal of our research was to generate transgenic plants with regulatory mechanism that perceives stress signals to optimize plant growth and biomass production in semi-stress field conditions.

     

New species of the buprestid genus <Emphasis Type="Italic">Endelus</Emphasis> Deyrolle (Coleoptera,Buprestidae) from China,India, and Laos

Endelus (Kubaniellus) indicus sp. n. from India, E. (K.) lao sp. n. and E. (K.) khnzoriani sp. n. from Laos, E. (s. str.) sausai sp. n. from China, and E. (s. str.) dembickyi sp. n. from India are described, the two latter species are included in the Endelus bicarinatus Théry, 1932 species-group recently established by the author. E. collinus Obenberger, 1922 is included in this group; lectotype of this species is designated. Keys to species of the subgenus Kubaniellus and of the E. collinus group are provided. E. (K.) kareni Kalashian is for the first time recorded for Shaanxi Prov., E. pacholatkoi Kalashian, E. smaragdinus Desc. et Vill., and E collinus Obenb., for Laos (the latter species, also for Myanmar).     

Genetic relationships of Chukchi charr <Emphasis Type="Italic">Salvelinus andriashevi</Emphasis> and Taranetz charr <Emphasis Type="Italic">Salvelinus taranetzi</Emphasis>

On the basis of sequence analysis of the mitochondrial DNA (mtDNA) control region (CR), cytochrome b (Cytb), and cytochrome oxidase-1 (CoI) genes, the relationships of endemic species Salvelinus andriashevi Berg, 1948, represented by the only population from Lake Estikhed (Chukotka), were estimated. The data on the genealogical analysis of mtDNA haplotypes supported phylogenetic closeness of S. andriashevi and S. taranetzi. It was also demonstrated that the specimens of Chukchi charr, along with Salvelinus sp. 4 (Lake Nachikinskoe), S. krogiusae (Lake Dal’nee), S. boganidae and S. elgyticus (Lake El’gygytgyn), and S. a. erythrinus from Canada’s Northwest Territories (NWT) belonged to the Arctic group of Taranetz charr. The problem of coincidence of taxonomic differentiation of charrs of the genus Salvelinus based on morphological and genetic analyses is discussed.     

<Emphasis Type="Italic">chr</Emphasis> genes from adaptive replicons are responsible for chromate resistance by <Emphasis Type="Italic">Burkholderia xenovorans</Emphasis> LB400

The chromate ion transporter (CHR) superfamily includes proteins that confer chromate resistance by extruding toxic chromate ions from cytoplasm. Burkholderia xenovorans strain LB400 encodes six CHR homologues in its multireplicon genome and has been reported as highly chromate-resistant. The objective of this work was to analyze the involvement of chr redundant genes in chromate resistance by LB400. It was found that B. xenovorans plant rhizosphere strains lacking the megaplasmid are chromate-sensitive, suggesting that the chr gene present in this replicon is responsible for the chromate-resistance phenotype of the LB400 strain. Transformation of a chromate-sensitive B. xenovorans strain with each of the six cloned LB400 chr genes showed that genes from ‘adaptive replicons’ (chrA1b and chr1NCb from chromosome 2 and chrA2 from the megaplasmid) conferred higher chromate resistance levels than chr genes from ‘central’ chromosome 1 (chrA1a, chrA6, and chr1NCa). An LB400 insertion mutant affected in the chrA2 gene displayed a chromate-sensitive phenotype, which was fully reverted by transferring the chrA2 wild-type gene, and partially reverted by chrA1b or chr1NCb genes. These data indicate that chr genes from adaptive replicons, mainly chrA2 from the megaplasmid, are responsible for the B. xenovorans LB400 chromate-resistance phenotype.