The export of amino acid in the phloem is altered in wheat plants lacking the short arm of chromosome 7B

Grain protein content is one of the major determinants of the baking and nutritional quality of wheat. It has previously been reported that the ditelosomic line of wheat (Triticum aestivum L.) CSDT7BL, where the short arm of chromosome 7B is missing, shows a lower grain protein concentration than the normal line, but a similar grain yield. In the present paper the growth and nitrogen (N) metabolism of wheat plants cv. Chinese Spring (CS) and its ditelosomic line CSDT7BL were compared. When plants were grown to maturity in pots with different N supplements, the wild-type line showed a higher grain protein concentration and a lower straw N concentration than the ditelosomic line at every N level analysed, suggesting a deficiency in the N remobilization capacity. When 15-d-old plants were grown in a growth cabinet in pots with sand, and supplied with nutrient solutions of different nitrate concentrations, the ditelosomic line showed no differences in N uptake per unit of root dry weight, nitrate reductase activity, nitrate, total N concentration or free amino acid concentration. However, the ditelosomic line showed a decreased capacity to export amino acids in the phloem under high N, independently of the N source. This deficiency was also observed under dark-induced senescence. The diminished export of amino acids to the phloem was principally caused by a decrease in the export of Glu, Asp, and Gln. It is suggested that the decrease in grain protein concentration in the ditelosomic line is a consequence of defective export in the phloem of these amino acids.     

Citrus Vascular Proteomics Highlights the Role of Peroxidases and Serine Proteases during Huanglongbing Disease Progression

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Highlights

• •HLB is the most devastating citrus disease associated with the pathogen CLas.
• •Proteases and peroxidases accumulated in plant vascular tissue after CLas infection.
• •Dynamic changes in serine protease activity occur across genotypes and environments.

     

Analysis of volatile compounds released from embryogenic cultures and somatic embryos of sweet oranges by head space SPME

Volatile compounds released from callus and nucellar embryo tissues of ‘Valencia late’ and ‘Washington Navel’ sweet oranges (Citrus sinensis, L. Osbeck) were collected/concentrated by head space solid phase micro extraction and analysed by gas chromatography-mass spectrometry. Friable, white embryogenic cultures released a number of volatile compounds, including some essential oils. Different samples of the same embryogenic culture showed variability, possibly related to the presence of tissues undergoing differentiation. Analyses of the somatic embryos permitted the identification of several components, including limonene and methyl anthranilate. Considering the simplicity and the very small sample required (0.3 g of fresh tissue) head space solid phase micro extraction is suitable for studies and comparisons of volatile metabolites released from in vitro Citrus tissue cultures suggesting its potential in Citrus biochemical, genetic and breeding research. This revised version was published online in June 2006 with corrections to the Cover Date.     

Brain Networks Responsible for Sense of Agency: An EEG Study

BackgroundSelf-agency (SA) is a person’s feeling that his action was generated by himself. The neural substrates of SA have been investigated in many neuroimaging studies, but the functional connectivity of identified regions has rarely been investigated. The goal of this study is to investigate the neural network related to SA.MethodsSA of hand movements was modulated with virtual reality. We examined the cortical network relating to SA modulation with electroencephalography (EEG) power spectrum and phase coherence of alpha, beta, and gamma frequency bands in 16 right-handed, healthy volunteers.ResultsIn the alpha band, significant relative power changes and phase coherence of alpha band were associated with SA modulation. The relative power decrease over the central, bilateral parietal, and right temporal regions (C4, Pz, P3, P4, T6) became larger as participants more effectively controlled the virtual hand movements. The phase coherence of the alpha band within frontal areas (F7-FP2, F7-Fz) was directly related to changes in SA. The functional connectivity was lower as the participants felt that they could control their virtual hand. In the other frequency bands, significant phase coherences were observed in the frontal (or central) to parietal, temporal, and occipital regions during SA modulation (Fz-O1, F3-O1, Cz-O1, C3-T4L in beta band; FP1-T6, FP1-O2, F7-T4L, F8-Cz in gamma band).ConclusionsOur study suggests that alpha band activity may be the main neural oscillation of SA, which suggests that the neural network within the anterior frontal area may be important in the generation of SA.     

An alternative method for the genetic transformation of sweet organce

Summary An alternative method for transforming sweet organe [Citrus sinensis (L.) Osbeck] has been developed. Plasmid DNA encoding the non-destructive selectable marker enhanced green fluorescent protein gene was introduced using polyethylene glycol into protoplasts of ‘Itaborai’ sweet organe isolated from an embryogenic nucellar-derived suspension culture. Following protoplast culture in liquid medium and transfer to solid medium, transformed calluses were identified via expression of the green fluorescent protein, physically separated from non-transformed tissue, and cultured on somatic embryogenesis induction medium. Transgenic plantlets were recovered from germinating somatic embryos and by in vitro rooting of shoots. To expedite transgenic plant recovery, regenerated shoots were also micrografted onto sour orange seedling rootstocks. Presence of the transgene in calluses and regenerated sweet organe plants was verified by gene amplification and Southern analyses. Potential advantages of this transformation system over the commonly used Agrobacterium methods for citrus are discussed.     

Genome-wide analyses of Liberibacter species provides insights into evolution,phylogenetic relationships,and virulence factors

‘Candidatus Liberibacter’ species are insect-transmitted, phloem-limited α-Proteobacteria in the order of Rhizobiales. The citrus industry is facing significant challenges due to huanglongbing, associated with infection from ‘Candidatus Liberibacter asiaticus’ (Las). In order to gain greater insight into ‘Ca. Liberibacter’ biology and genetic diversity, we have performed genome sequencing and comparative analyses of diverse ‘Ca. Liberibacter’ species, including those that can infect citrus. Our phylogenetic analysis differentiates ‘Ca. Liberibacter’ species and Rhizobiales in separate clades and suggests stepwise evolution from a common ancestor splitting first into nonpathogenic Liberibacter crescens followed by diversification of pathogenic ‘Ca. Liberibacter’ species. Further analysis of Las genomes from different geographical locations revealed diversity among isolates from the United States. Our phylogenetic study also indicates multiple Las introduction events in California and spread of the pathogen from Florida to Texas. Texan Las isolates were closely related, while Florida and Asian isolates exhibited the most genetic variation. We have identified conserved Sec translocon (SEC)-dependent effectors likely involved in bacterial survival and virulence of Las and analysed their expression in their plant host (citrus) and insect vector (Diaphorina citri). Individual SEC-dependent effectors exhibited differential expression patterns between host and vector, indicating that Las uses its effector repertoire to differentially modulate diverse organisms. Collectively, this work provides insights into the evolution of ‘Ca. Liberibacter’ species, the introduction of Las in the United States and identifies promising Las targets for disease management.     

An integrated proteomic and metabolomic study to evaluate the effect of nucleus-cytoplasm interaction in a diploid citrus cybrid between sweet orange and lemon

Key message

Our results provide a comprehensive overview how the alloplasmic condition might lead to a significant improvement in citrus plant breeding, developing varieties more adaptable to a wide range of conditions.

Abstract

Citrus cybrids resulting from somatic hybridization hold great potential in plant improvement. They represent effective products resulting from the transfer of organelle-encoded traits into cultivated varieties. In these cases, the plant coordinated array of physiological, biochemical, and molecular functions remains the result of integration among different signals, which derive from the compartmentalized genomes of nucleus, plastids and mitochondria. To dissect the effects of genome rearrangement into cybrids, a multidisciplinary study was conducted on a diploid cybrid (C2N), resulting from a breeding program aimed to improve interesting agronomical traits for lemon, the parental cultivars ‘Valencia’ sweet orange (V) and ‘femminello’ lemon (F), and the corresponding somatic allotetraploid hybrid (V?+?F). In particular, a differential proteomic analysis, based on 2D-DIGE and MS procedures, was carried out on leaf proteomes of C2N, V, F and V?+?F, using the C2N proteome as pivotal condition. This investigation revealed differentially represented protein patterns that can be associated with genome rearrangement and cell compartment interplay. Interestingly, most of the up-regulated proteins in the cybrid are involved in crucial biological processes such as photosynthesis, energy production and stress tolerance response. The cybrid differential proteome pattern was concomitant with a general increase of leaf gas exchange and content of volatile organic compounds, highlighting a stimulation of specific pathways that can be related to observed plant performances. Our results contribute to a better understanding how the alloplasmic condition might lead to a substantial improvement in plant breeding, opening new opportunities to develop varieties more adaptable to a wide range of conditions.

     

The effect of inoculation with Azospirillum brasilense on growth and nitrogen utilization by wheat plants

Azospirillium brasilense is a rhizosphere bacteria that has been reported to improve yield when inoculated on wheat plants. However, the mechanisms through which this effect is induced is still unclear. In the present work, we have studied the effects of inoculating a highly efficient A. brasilense strain on wheat plant grown in 5 kg pots with soil in a greenhouse, under three N regimes (0, 3 or 16 mM NO₃ ^–, 50 ml/pot once or twice-a -week), and in disinfected or non-disinfected soil. At the booting stage, the inoculated roots in both soils showed a similar colonization by Azospirillum sp. that was not affected by N addition. The plants grown in the disinfected soil showed a higher biomass, N content and N concentration than those in the non-disinfected soil, and in both soils the inoculation stimulated plant growth, N accumulation, and N and NO₃ ^– concentration in the tissues.At maturity, the inoculated plants showed a higher biomass, grain yield and N content than the uninoculated ones in both soils, and a higher grain protein concentration than the uninoculated. It is concluded that in the present experiments, A. brasilenseincreased plant growth by stimulating nitrogen uptake by the roots.