[Show abstract][Hide abstract] ABSTRACT: Chloride (Cl–) is a micronutrient that accumulates to macronutrient levels since it is normally available in nature and actively taken
up by higher plants. Besides a role as an unspecific cell osmoticum, no clear biological roles have been explicitly associated
with Cl– when accumulated to macronutrient concentrations. To address this question, the glycophyte tobacco (Nicotiana tabacum L. var. Habana) has been treated with a basal nutrient solution supplemented with one of three salt combinations containing
the same cationic balance: Cl–-based (CL), nitrate-based (N), and sulphate+phosphate-based (SP) treatments. Under non-saline conditions (up to 5mM Cl–) and no water limitation, Cl– specifically stimulated higher leaf cell size and led to a moderate increase of plant fresh and dry biomass mainly due to
higher shoot expansion. When applied in the 1–5mM range, Cl– played specific roles in regulating leaf osmotic potential and turgor, allowing plants to improve leaf water balance parameters.
In addition, Cl– also altered water relations at the whole-plant level through reduction of plant transpiration. This was a consequence of
a lower stomatal conductance, which resulted in lower water loss and greater photosynthetic and integrated water-use efficiency.
In contrast to Cl–, these effects were not observed for essential anionic macronutrients such as nitrate, sulphate, and phosphate. We propose
that the abundant uptake and accumulation of Cl– responds to adaptive functions improving water homeostasis in higher plants.
Full-text · Article · Nov 2015 · Journal of Experimental Botany
[Show abstract][Hide abstract] ABSTRACT: Organ abscission is an important process in plant development and reproduction. During abscission, changes in cellular adhesion of specialized abscission zone cells ensure the detachment of infected organs or those no longer serving a function to the plant. In addition, abscission also plays an important role in the release of ripe fruits. Different plant species display distinct patterns and timing of organ shedding, most likely adapted during evolution to their diverse life styles. However, it appears that key regulators of cell separation may have conserved function in different plant species. Here, we investigate the functional conservation of the citrus ortholog of the Arabidopsis peptide ligand INFLORESCENCE DEFICIENT IN ABSCISSION (AtIDA), controlling floral organ abscission. We discuss the possible implications of modifying the citrus IDA ortholog for citrus fruit production.
Full-text · Article · Nov 2015 · Frontiers in Plant Science
[Show abstract][Hide abstract] ABSTRACT: For grafted plants, salt stress tolerance of the aerial plant part is poorly documented. Thus, we developed a simple, fast and inexpensive method to identify tolerant genotypes. Twigs of 14 mandarin accessions that we previously analyzed as seedlings were cut in solution to prevent embolism and were then evaluated in salt stress condition for a week. Physiological parameters such as gas exchanges, leaf Cl(-) and Na(+), as well as the presence of H2O2 and the activity of enzymes involved in ROS synthesis and detoxification processes were analyzed. One accession known to be tolerant as rootstock was shown to be sensitive with limited Cl(-) translocation from the solution to the shoot while sensitive accessions when grown as seedlings presented limited wilting symptoms and accumulated large leaf Cl(-) content. A model is proposed to explain the different strategies of the plant to cope with high toxic ion content. This method allows separation of the root compartment, where ion exclusion mechanisms may exist and have an impact on the salt stress tolerance of the whole plant.
Full-text · Article · Nov 2015 · Journal of plant physiology
[Show abstract][Hide abstract] ABSTRACT: RNA-seq studies in citrus have focused on physiological processes relevant for fruit quality and productivity of the major species, especially sweet orange. However, little or no attention has been paid to vegetative or reproductive tissues, and most of the Citrus species have never been analyzed. In this work we characterized the transcriptome of vegetative and reproductive tissues from a wide representation of Citrus species, with members from all the main phylogenetic groups. Our aims were to acquire a complete view of the citrus transcriptome landscape, to improve previous functional annotations and to obtain genetic markers (SNPs and Indels) associated to genes of agronomic interest.
28 samples were used for RNA-Seq analysis, obtained from 12 citrus species: C. medica, C. aurantifolia, C. limon, C. bergamia, C. clementina, C. deliciosa, C. reshni, C. maxima, C. paradisi, C. aurantium, C. sinensis, and Poncirus trifoliata. Four different organs were analyzed: root, bark, leaf, and flower.
A total of 3421 million Illumina reads were produced and mapped against the reference C. clementina genome sequence. Transcript discovery pipeline revealed 3326 new genes, the number of genes with alternative splicing was increased to 19739, and a total of 73797 transcripts were identified, which represents a 3 fold increase with respect the previous results from C. clementina.
Differential expression studies between the 4 tissues were performed with EDGE-R. Variants discovery analysis revealed the presence of indels and SNPs in genes relevant for fruit quality and productivity that could be used for breeding. Some relevant pathways in citrus were also analyzed: flavonoids and flavonols, ethylene and auxin.
[Show abstract][Hide abstract] ABSTRACT: Mandarin is an important genetic group in citrus largely used for variety breeding programs and also to generate new rootstocks better adapted to abiotic stress. In this study, 14 mandarin accessions representative of the diversity in this group were analyzed for their salt stress tolerance properties. Physiological parameters such as gas exchange, osmotic pressure, as well as leaf and root chloride contents were measured. Samples were harvested to characterize the presence of hydrogen peroxide and to monitor the activity of enzymes involved in reactive oxygen species synthesis and detoxification processes. Very different physiological behaviors were noted among accessions. Most cultivars that are used as rootstocks such as Citrus reshni Hort. ex Tan. (‘Cleopatra’) or Citrus depressa Hayata (‘Shekwasha’), were found to be tolerant, with limited root-to-shoot chloride translocation. Also, some accessions used as varieties showed similar tolerance traits. Interestingly some accessions that presented high leaf chloride contents were not always associated with sensitivity traits. Also accessions such as ‘Willowleaf’ showed quite high leaf chloride contents that were correlated with better detoxification processes. Tolerance traits that we identified are discussed in relation to the known genetic structure in mandarins. Finally, some of the salt stress tolerant accessions that we identified could potentially be used as parents in rootstock breeding programs and others in scion variety breeding programs.
Full-text · Article · Aug 2015 · Scientia Horticulturae
[Show abstract][Hide abstract] ABSTRACT: Trifoliate orange (Poncirus trifoliata (L.) Raf.) is a very useful taxon for the citrus industry since this rootstock is immune to the Citrus Tristeza virus and confers cold tolerance. Numerous trifoliate orange varieties exist but little is known regarding their behavioural variability when subjected to abiotic constraints. The diversity of 74 P. trifoliata accessions maintained in the INRA-CIRAD Citrus Germplasm Collection was investigated using simple sequence repeat markers. Two major genetic groups were clearly identified as a few homonyms, intergroup or intra-group hybrids and doubled-chromosome tetraploid forms. The Group 1 phenotype was characterized by larger flowers and leaves and smaller seeds than Group 2. Tetraploid accessions showed larger leaves and heavier seeds than all other diploid accessions, regardless of genetic classification. Eight genotypes belonging to both genetic groups, as well as two hybrids between the two groups, were selected to investigate their water deficit tolerance. Stress was applied by withdrawing irrigation for 4 weeks. Physiological parameters such as leaf stomatal conductance, quantum yield of photosystem II electron transport, soil water potential, leaf osmotic potential and transpiration rate were estimated. Some varieties, such as Rubidoux 0101033, were clearly more tolerant to water deficit than others, such as Pomeroy 0101040 and Pomeroy 0110081. Interestingly, accessions that had the highest soil water potential and were the least affected by stress belonged to genetic Group 2. Conversely, trifoliate oranges of genetic Group 1 were the least tolerant.
No preview · Article · Mar 2015 · The Journal of Agricultural Science
[Show abstract][Hide abstract] ABSTRACT: Transposable-element mediated chromosomal rearrangements require the involvement of two transposons and two double-strand breaks (DSB) located in close proximity. In radiobiology, DSB proximity is also a major factor contributing to rearrangements. However, the whole issue of DSB proximity remains virtually unexplored.
Based on DNA sequencing analysis we show that the genomes of 2 derived mutations, Arrufatina (sport) and Nero (irradiation), share a similar 2 Mb deletion of chromosome 3. A 7 kb Mutator-like element found in Clemenules was present in Arrufatina in inverted orientation flanking the 5' end of the deletion. The Arrufatina Mule displayed "dissimilar" 9-bp target site duplications separated by 2 Mb. Fine-scale single nucleotide variant analyses of the deleted fragments identified a TTC-repeat sequence motif located in the center of the deletion responsible of a meiotic crossover detected in the citrus reference genome.
Taken together, this information is compatible with the proposal that in both mutants, the TTC-repeat motif formed a triplex DNA structure generating a loop that brought in close proximity the originally distinct reactive ends. In Arrufatina, the loop brought the Mule ends nearby the 2 distinct insertion target sites and the inverted insertion of the transposable element between these target sites provoked the release of the in-between fragment. This proposal requires the involvement of a unique transposon and sheds light on the unresolved question of how two distinct sites become located in close proximity. These observations confer a crucial role to the TTC-repeats in fundamental plant processes as meiotic recombination and chromosomal rearrangements.
[Show abstract][Hide abstract] ABSTRACT: Plants are constantly exposed to stress factors. Biotic stress is produced by living organisms such as pathogens, whereas abiotic stress by unfavourable environmental conditions. In Citrus species, one of the most important fruit crops in the world, these stresses generate serious limitations in productivity. Through biochemical and transcriptomic assays, we had previously characterised the Citrus sinensis (L.) Osbeck nonhost response to Xanthomonas campestris pv. vesicatoria (Doidge), in contrast to Asiatic citrus canker infection caused by Xanthomonas citri subsp. citri (Hasse). A hypersensitive response (HR) including changes in the expression of several transcription factors was reported. Here, a new exhaustive analysis of the Citrus sinensis transcriptomes previously obtained was performed, allowing us to detect the over-representation of photosynthesis, abiotic stress and secondary metabolism processes during the nonhost HR. The broad downregulation of photosynthesis-related genes was correlated with an altered photosynthesis physiology. The high number of heat shock proteins and genes related to abiotic stress, including aquaporins, suggests that stresses crosstalk. Additionally, the secondary metabolism exhibited lignin and carotenoid biosynthesis modifications and expression changes in the cell rescue GSTs. In conclusion, novel features of the Citrus nonhost HR, an important part of the plants' defence against disease that has yet to be fully exploited in plant breeding programs, are presented.
Full-text · Article · Jan 2015 · Functional Plant Biology