Somaclonal variation versus chemically induced mutagenesis in tomato (Lycopersicon esculentum L.)

Summary A comparison was made of the type and frequency of mutational events found in the progeny of tomato plants regenerated after one passage in vitro with those induced by chemical mutagenesis with ethyl methane sulphonate. Several mutants were recovered in the progeny of regenerated and mutagenized plants of two cultivars of tomato. They can be grouped into the following categories: seedling lethality, male sterility, resistance to Verticillium, short stature, change in number of lateral shoots or in leaf shape. The results indicate that the two sources of variability differ in their effect, changing the spectrum and frequency of the mutants as well as, at least in some cases, their pattern of segregation.     

Genetic relationship between o6 and pro-1 mutants in maize

Summary This paper reports that the opaque-6 (o6) mutation of maize, which causes seedling lethality and interferes in the endosperm with the synthesis of zeins and b-32 protein, is a proline requiring mutant functionally allelic to proline-1 (pro-1). Furthermore, immunological studies on the b-32 content of ten independently originated o6 and pro-1 alleles demonstrated that four alleles contain an apparently normal b-32 protein while the others are either devoid of it or contain trace amounts of cross-reacting proteins of lower molecular weight.     

Alterations in G-proteins in congestive heart failure in cardiomyopathic (UM-X7.1) hamsters

In order to explain the attenuated sympathetic support during the development of heart failure, the status of -adrenergic mechanisms in the failing myocardium was assessed by employing cardiomyopathic hamsters (155–170 days old) at moderate degree of congestive heart failure. The norepinephrine turnover rate was increased but the norepinephrine content was decreased in cardiomyopathic hearts. The number and the affinity of receptors in the sarcolemmal preparations were not changed in these hearts at moderate stage of congestive heart failure. While the basal adenylyl cyclase activity was not altered in sarcolemma, the stimulation of enzyme activity by NaF, forskolin, Gpp(NH)p or epinephrine was depressed in hearts from these cardiomyopathic hamsters. Since G-proteins are involved in modifying the adenylyl cyclase activity, the functional and bioactivities as well as contents of both Gs and Gi proteins were determined in the cardiomyopathic heart sarcolemma. The functional stimulation of adenylyl cyclase by cholera toxin, which activates Gs proteins, was markedly depressed whereas that by Pertussis toxin, which inhibits Gi proteins, was markedly augmented in cardiomyopathic hearts. The cholera toxin and pertussis toxin catalyzed ADP-ribosylation was increased by 37 and 126%, respectively; this indicated increased bioactivities of both Gs and Gi proteins in experimental preparations. The immunoblot analysis suggested 74 and 124% increase in Gs and Gi contents in failing hearts, respectively. These results suggest that depressed adenylyl cyclase activation in cardiomyopathic hamsters may not only be due to increased content and bioactivity of Gi proteins but the functional uncoupling of Gs proteins from the adenylyl cyclase enzyme may also be involved at this stage of heart failure.     

Effectiveness of acoustic “prey”: Environmental enrichment for a captive African leopard (Panthera pardus)

In the course of developing active naturalistic exercise opportunities for zoo felines at moderate cost, a computer-controlled acoustic prey device was established. Changes in the behavior of a 16-year-old melanistic leopard (Sabrina) were studied as she learned to actively pursue bird sounds and obtained food treats as a function of the activity. By the twenty-ninth day she began to capture all 24 bird parts supplied on the feeder belt and continues to actively use the opportunity on a daily basis. General activity and apparent well-being have been enhanced, while stereotypic behaviors have decreased. © 1995 Wiley-Liss, Inc.     

Natural Variation in Maize Aphid Resistance Is Associated with 2,4-Dihydroxy-7-Methoxy-1,4-Benzoxazin-3-One Glucoside Methyltransferase Activity

Plants differ greatly in their susceptibility to insect herbivory, suggesting both local adaptation and resistance tradeoffs. We used maize (Zea mays) recombinant inbred lines to map a quantitative trait locus (QTL) for the maize leaf aphid (Rhopalosiphum maidis) susceptibility to maize Chromosome 1. Phytochemical analysis revealed that the same locus was also associated with high levels of 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one glucoside (HDMBOA-Glc) and low levels of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one glucoside (DIMBOA-Glc). In vitro enzyme assays with candidate genes from the region of the QTL identified three O-methyltransferases (Bx10a-c) that convert DIMBOA-Glc to HDMBOA-Glc. Variation in HDMBOA-Glc production was attributed to a natural CACTA family transposon insertion that inactivates Bx10c in maize lines with low HDMBOA-Glc accumulation. When tested with a population of 26 diverse maize inbred lines, R. maidis produced more progeny on those with high HDMBOA-Glc and low DIMBOA-Glc. Although HDMBOA-Glc was more toxic to R. maidis than DIMBOA-Glc in vitro, BX10c activity and the resulting decline of DIMBOA-Glc upon methylation to HDMBOA-Glc were associated with reduced callose deposition as an aphid defense response in vivo. Thus, a natural transposon insertion appears to mediate an ecologically relevant trade-off between the direct toxicity and defense-inducing properties of maize benzoxazinoids.     

An in vitro network of intermolecular interactions between viral RNA segments of an avian H5N2 influenza A virus: comparison with a human H3N2 virus

The genome of influenza A viruses (IAV) is split into eight viral RNAs (vRNAs) that are encapsidated as viral ribonucleoproteins. The existence of a segment-specific packaging mechanism is well established, but the molecular basis of this mechanism remains to be deciphered. Selective packaging could be mediated by direct interaction between the vRNA packaging regions, but such interactions have never been demonstrated in virions. Recently, we showed that the eight vRNAs of a human H3N2 IAV form a single interaction network in vitro that involves regions of the vRNAs known to contain packaging signals in the case of H1N1 IAV strains. Here, we show that the eight vRNAs of an avian H5N2 IAV also form a single network of interactions in vitro, but, interestingly, the interactions and the regions of the vRNAs they involve differ from those described for the human H3N2 virus. We identified the vRNA sequences involved in five of these interactions at the nucleotide level, and in two cases, we validated the existence of the interaction using compensatory mutations in the interacting sequences. Electron tomography also revealed significant differences in the interactions taking place between viral ribonucleoproteins in H5N2 and H3N2 virions, despite their canonical ‘7 + 1’ arrangement.     

Evolutionary Dynamics of the Leucine-Rich Repeat Receptor-Like Kinase (LRR-RLK) Subfamily in Angiosperms

Gene duplications are an important factor in plant evolution, and lineage-specific expanded (LSE) genes are of particular interest. Receptor-like kinases expanded massively in land plants, and leucine-rich repeat receptor-like kinases (LRR-RLK) constitute the largest receptor-like kinases family. Based on the phylogeny of 7,554 LRR-RLK genes from 31 fully sequenced flowering plant genomes, the complex evolutionary dynamics of this family was characterized in depth. We studied the involvement of selection during the expansion of this family among angiosperms. LRR-RLK subgroups harbor extremely contrasting rates of duplication, retention, or loss, and LSE copies are predominantly found in subgroups involved in environmental interactions. Expansion rates also differ significantly depending on the time when rounds of expansion or loss occurred on the angiosperm phylogenetic tree. Finally, using a d_N/d_S-based test in a phylogenetic framework, we searched for selection footprints on LSE and single-copy LRR-RLK genes. Selective constraint appeared to be globally relaxed at LSE genes, and codons under positive selection were detected in 50% of them. Moreover, the leucine-rich repeat domains, and specifically four amino acids in them, were found to be the main targets of positive selection. Here, we provide an extensive overview of the expansion and evolution of this very large gene family.Receptor-like kinases (RLKs) constitute one of the largest gene families in plants and expanded massively in land plants (Embryophyta; Lehti-Shiu et al., 2009, 2012). For plant RLK gene families, the functions of most members are often not known (especially in recently expanded families), but some described functions include innate immunity (Albert et al., 2010), pathogen response (Dodds and Rathjen, 2010), abiotic stress (Yang et al., 2010), development (De Smet et al., 2009), and sometimes multiple functions (Lehti-Shiu et al., 2012). The RLKs usually consist of three domains: an N-terminal extracellular domain, a transmembrane domain, and a C-terminal kinase domain (KD). In plants, the KD usually has a Ser/Thr specificity (Shiu and Bleecker, 2001), but Tyr-specific RLKs were also described (e.g. BRASSINOSTEROID INSENSITIVE1; Oh et al., 2009). Interestingly, it was estimated that approximately 20% of RLKs contain a catalytically inactive KD (e.g. STRUBBELIG and CORYNE; Chevalier et al., 2005; Castells and Casacuberta, 2007; Gish and Clark, 2011). In Arabidopsis (Arabidopsis thaliana), 44 RLK subgroups (SGs) were defined by inferring the phylogenetic relationships between the KDs (Shiu and Bleecker, 2001). Interestingly, different SGs show different duplication/retention rates (Lehti-Shiu et al., 2009). Specifically, RLKs involved in stress responses show a high number of tandemly duplicated genes whereas those involved in development do not (Shiu et al., 2004), which suggests that some RLK genes are important for the responses of land plants to a changing environment (Lehti-Shiu et al., 2012). There seem to be relatively few RLK pseudogenes compared with other large gene families, and copy retention was argued to be driven by both drift and selection (Zou et al., 2009; Lehti-Shiu et al., 2012). As most SGs are relatively old and RLK subfamilies expanded independently in several plant lineages, duplicate retention cannot be explained by drift alone, and natural selection is expected to be an important driving factor in RLK gene family retention (Lehti-Shiu et al., 2009).Leucine-rich repeat-receptor-like kinases (LRR-RLKs), which contain up to 30 leucine-rich repeat (LRRs) in their extracellular domain, constitute the largest RLK family (Shiu and Bleecker, 2001). Based on the KD, 15 LRR-RLK SGs have been established in Arabidopsis (Shiu et al., 2004; Lehti-Shiu et al., 2009). So far, two major functions have been attributed to them: defense against pathogens and development (Tang et al., 2010b). LRR-RLKs involved in defense are predominantly found in lineage-specific expanded (LSE) gene clusters, whereas LRR-RLKs involved in development are mostly found in nonexpanded groups (Tang et al., 2010b). It was also discovered that the LRR domains are significantly less conserved than the remaining domains of the LRR-RLK genes (Tang et al., 2010b). In addition, a study of four plant genomes (Arabidopsis, grape [Vitis vinifera], poplar [Populus trichocarpa], and rice [Oryza sativa]) showed that LRR-RLK genes from LSE gene clusters show significantly more indications of positive selection or relaxed constraint than LRR-RLKs from nonexpanded groups (Tang et al., 2010b).The genomes of flowering plants (angiosperms) have been shown to be highly dynamic compared with most other groups of land plants (Leitch and Leitch, 2012). This dynamic is mostly caused by the frequent multiplication of genetic material, followed by a complex pattern of differential losses (i.e. the fragmentation process) and chromosomal rearrangements (Langham et al., 2004; Leitch and Leitch, 2012). Most angiosperm genomes sequenced so far show evidence for at least one whole-genome multiplication event during their evolution (Jaillon et al., 2007; D’Hont et al., 2012; Tomato Genome Consortium, 2012). At a smaller scale, tandem and segmental duplications are also very common in angiosperms (Arabidopsis Genome Initiative, 2000; International Rice Genome Sequencing Project, 2005; Rizzon et al., 2006). Although the most common fate of duplicated genes is to be progressively lost, in some cases they can be retained in the genome, and adaptive as well as nonadaptive scenarios have been discussed to play a role in this preservation process (for review, see Moore and Purugganan, 2005; Hahn, 2009; Innan, 2009; Innan and Kondrashov, 2010). Whole-genome sequences also revealed that the same gene may undergo several rounds of duplication and retention. These LSE genes were shown to evolve under positive selection more frequently than single-copy genes in angiosperms (Fischer et al., 2014). That study analyzed general trends over whole genomes. Here, we ask if, and to what extent, this trend is observable at LRR-RLK genes. As this gene family is very dynamic and large, and in accordance with the results of Tang et al. (2010b), we expect the effect of positive selection to be even more pronounced than in the whole-genome average.We analyzed 33 Embryophyta genomes to investigate the evolutionary history of the LRR-RLK gene family in a phylogenetic framework. Twenty LRR-RLK SGs were identified, and from this data set, we deciphered the evolutionary dynamics of this family within angiosperms. The expansion/reduction rates were contrasted between SGs and species as well as in ancestral branches of the angiosperm phylogeny. We then focused on genes whose number increased dramatically in an SG- and/or species-specific manner (i.e. LSE genes). Those genes are likely to be involved in species-specific cellular processes or adaptive interactions and were used as a template to infer the potential occurrence of positive selection. This led to the identification of sites at which positive selection likely acted. We discuss our results in the light of angiosperm genome evolution and current knowledge of LRR-RLK functions. Positive selection footprints identified in LSE genes highlight the importance of combining evolutionary analysis and functional knowledge to guide further investigations.