Breeding system in a population of Trigonella balansae (Leguminosae)

BACKGROUND AND AIMS: Although some taxonomic studies in the genus Trigonella have been conducted, there has been no concerted effort to study the breeding system. This paper examines the floral structure and pollination system in a population of T. balansae, an annual pasture legume. METHODS: Floral morphology, hand and vector pollination, stigma receptivity, pollen tube growth, using scanning electron and fluorescence microscopy, were conducted. KEY RESULTS: Measurements of floral structure from before to after anthesis indicates an inability for T. balansae to self-pollinate and a requirement for an external vector to effectively transfer pollen from the anthers onto the stigmas of this species. Seed set can be obtained by hand or honeybee manipulation of T. balansae flowers. CONCLUSIONS: Trigonella balansae is a self-compatible species, but which requires vectors such as honeybees to bring about pollination.     

Biochemical characterization of transgenic tomato plants in which carotenoid synthesis has been inhibited through the expression of antisense RNA to pTOM5

Transgenic tomato plants expressing antisense RNA to a ripening-related cDNA clone (pTOM5) had yellow ripening fruit and pale coloured flowers. Carotenoid levels in fruit of these plants were reduced by up to 97%. In order to determine the step of carotenoid biosynthesis which was blocked, a cell-free system active in the synthesis of carotenoid intermediates was prepared. Incubations with radiolabelled carotenoid precursors led to the identification of the block between GGDP and phytoene. Analysis of carotenoids in different tissues of transgenic and control plants indicated that although ripe fruit and flower carotenoid levels were reduced in the modified plants, leaf carotenoid levels were not decreased. This implies that the pTOM5 gene product is not involved in carotenoid synthesis in the leaf.     

Jasmonoyl‐l‐isoleucine hydrolase 1 (JIH1) regulates jasmonoyl‐l‐isoleucine levels and attenuates plant defenses against herbivores

For most plant hormones, biological activity is suppressed by reversible conjugation to sugars, amino acids and other small molecules. In contrast, the conjugation of jasmonic acid (JA) to isoleucine (Ile) is known to enhance the activity of JA. Whereas hydroxylation and carboxylation of JA‐Ile permanently inactivates JA‐Ile‐mediated signaling in plants, the alternative deactivation pathway of JA‐Ile by its direct hydrolysis to JA remains unstudied. We show that Nicotiana attenuata jasmonoyl‐l ‐isoleucine hydrolase 1 (JIH1), a close homologue of previously characterized indoleacetic acid alanine resistant 3 (IAR3) gene in Arabidopsis, hydrolyzes both JA‐Ile and IAA‐Ala in vitro. When the herbivory‐inducible NaJIH1 gene was silenced by RNA interference, JA‐Ile levels increased dramatically after simulated herbivory in irJIH1, compared with wild‐type (WT) plants. When specialist (Manduca sexta) or generalist (Spodoptera littoralis) herbivores fed on irJIH1 plants they gained significantly less mass compared with those feeding on wild‐type (WT) plants. The poor larval performance was strongly correlated with the higher accumulation of several JA‐Ile‐dependent direct defense metabolites in irJIH1 plants. In the field, irJIH1 plants attracted substantially more Geocoris predators to the experimentally attached M. sexta eggs on their leaves, compared with empty vector plants, which correlated with higher herbivory‐elicited emissions of volatiles known to function as indirect defenses. We conclude that NaJIH1 encodes a new homeostatic step in JA metabolism that, together with JA and JA‐Ile‐hydroxylation and carboxylation of JA‐Ile, rapidly attenuates the JA‐Ile burst, allowing plants to tailor the expression of direct and indirect defenses against herbivore attack in nature.     

Chloroplast Structure and Function Is Altered in the NCS2 Maize Mitochondrial Mutant

The nonchromosomal stripe 2 (NCS2) mutant of maize (Zea mays L.) has a DNA rearrangement in the mitochondrial genome that segregates with the abnormal growth phenotype. Yet, the NCS2 characteristic phenotype includes striped sectors of pale-green tissue on the leaves. This suggests a chloroplast abnormality. To characterize the chloroplasts present in the mutant sectors, we examined the chloroplast structure by electron microscopy, chloroplast function by radiolabeled carbon dioxide fixation and fluorescence induction kinetics, and thylakoid protein composition by polyacrylamide gel electrophoresis. The data from these analyses suggest abnormal or prematurely arrested chloroplast development. Deleterious effects of the NCS2 mutant mitochondria upon the cells of the leaf include structural and functional alterations in the both the bundle sheath and mesophyll chloroplasts.     

Genetic structures of the CIMMYT international yield trial targeted to irrigated environments

International yield trials are assembled by CIMMYT to disseminate promising wheat breeding materials worldwide. To assess the genomic structure and linkage disequilibrium (LD) within this germplasm, wheat lines disseminated during 25 years of the Elite Spring Wheat Yield Trial (ESWYT) targeted for irrigated environments of the world were genotyped with the high-throughput Diversity Arrays Technology (DArT) marker system. Analyses of population structure assigned the ESWYT germplasm into five major sub-populations that are shaped by prominent CIMMYT wheat lines and their descendants. Based on genetic distance, we concluded that a constant level of genetic diversity was maintained over the years of ESWYT dissemination. Genetic distance between the individual ESWYT lines significantly increased when the ESWYT were grouped according to the differences in years of ESWYT dissemination, suggesting a systematic change in allele frequencies over time, most probably due to breeding and directional selection. By means of multiple regression analyses, 78 markers displaying a significant change in allele frequency across years were identified and interpreted as an indicator for constant selection. The markers identified were partly associated with grain yield, leaf, stem, and yellow rust and point to key genomic regions for further investigation. Large numbers of adjacent DArT marker pairs showed significant LD across the ESWYT population and within each of the five sub-populations identified. Sub-population differentiation measured by the fixation index and average genetic distance were highly correlated with LD levels, suggesting that the sub-populations themselves explain much of the LD.     

Human impacts and the global distribution of extinction risk

Understanding the global geographical distribution of extinction risk is a key challenge in conservation biology. It remains controversial, however, to what extent areas become threat hotspots simply because of high human impacts or due to predisposing ecological conditions. Limits to the taxonomic and geographical extent, resolution and quality of previously available data have precluded a full global assessment of the relative roles of these factors. Here, we use a new global database on the geographical distributions of birds on continents and continental islands to show that, after controlling for species richness, the best predictors of the global pattern of extinction risk are measures of human impact. Ecological gradients are of secondary importance at a global scale. The converse is true for individual biogeographic realms, within which variation in human impact is reduced and its influence on extinction risk globally is therefore underestimated. These results underline the importance of a global perspective on the mechanisms driving spatial patterns of extinction risk, and the key role of anthropogenic factors in driving the current extinction crisis.     

The isolation of Ant1, a transposable element from Aspergillus niger

A transposable element has been isolated from the industrially important fungus Aspergillus niger (strain N402). The element was identified as an insertion sequence within the coding region of the nitrate reductase gene. It had inserted at a TA site and appeared to have duplicated the target site upon insertion. The isolated element was found to be 4798 by in length and contained 37-bp inverted, imperfect, terminal repeats (ITRs). The sequence of the central region of the element revealed an open reading frame (designated ORF1) which showed similarity, at the amino acid level, to the transposase of the Tc1/mariner class of DNA transposons. Another sequence within the central region of the element showed similarity to the 3 coding and downstream untranslated region of the amyA gene of A. niger. Sequence homology and structural features indicate that this element, which has been named Ant1 (A. niger transposon 1), is related to the Tc1/mariner group of DNA transposons. Ant1 is apparently present as a single copy in strain N402 of A. niger.