Functional Quality and Radical Scavenging Activity of Selected Watermelon (Citrullus lanatus (Thunb.) Mansfeld) Genotypes as Affected by Early and Full Cropping Seasons.

Growing conditions and seasonal fluctuations are critical factors affecting fruit and vegetable nutritional quality. The effects of two partially overlapping cropping seasons, early (ECS; January-May) and full (FCS; March-July), on the main carpometric traits and bioactive components of different watermelon fruits were investigated in the open field. Four watermelon genotypes, comprising of three commercial cultivars 'Crimson Sweet', 'Dumara', 'Giza', and the novel hybrid 'P503 F1', were compared. The carpometric traits varied significantly between genotypes. Soluble solids and yield were higher under FCS than ECS. The variation affecting colour indexes between the two growing seasons exhibited a genotype-dependent trend. The antioxidant components and radical scavenging activity of watermelon fruits were also significantly affected by differences in received solar energy and temperature fluctuations during the trial period. The average citrulline, total phenolics and flavonoid contents were 93%, 71% and 40% higher in FCS than in ECS. A genotype-dependent variation trend was also observed for lycopene and total vitamin C between cropping seasons. The hydrophilic and lipophilic radical scavenging activities of the pulp of ripe watermelon fruits of the different genotypes investigated varied between 243.16 and 425.31 µmol Trolox Equivalent (TE) of 100 g-1 of fresh weight (fw) and from 232.71 to 341.67 µmol TE of 100 g-1 fw in FCS and ECS, respectively. Our results, although preliminary, show that the functional quality of watermelon fruits is drastically altered depending on the environmental conditions that characterize the ECS and LCS.

The Plant Growth-Promoting Bacteria Strain Bacillus mojavensis I4 Enhanced Salt Stress Tolerance in Durum Wheat.

Plant growth and production are adversely affected by soil salinity. A plant growth-promoting bacteria (PGPB) designated as the "I4 strain" of Bacillus mojavensis was isolated from Tunisian soil (Sfax, Tunisia) and showed the ability to be grown in the presence of NaCl concentrations ranging from 0 to 10% in Luria Bertani (LB) medium. The PGPB-mediated salt tolerance in durum wheat was evaluated. The physiological parameters such as growth, shoot and root length, dry and fresh weight were higher in I4-inoculated wheat plants in comparison with non-treated plants under salt stress. Results showed that this strain promoted wheat growth and preserved the membrane damage by notably lowering the electrolytes leakage and malondialdehyde content in contrast to non-inoculated plants. Moreover, leaf chlorophyll content, biochemical parameters and antioxidant enzyme activities measurement showed a better salt and heavy metal stress adaptation of the I4-inoculated plants. Due to these outcomes, it could be suggested that the inoculation of the PGPB I4 strain enhanced the wheat plant's growth, especially under salt stress conditions. This study confirms the ameliorative role played by PGPB in tolerating salt stress in wheat and their potential use as biofertilizers to enhance its growth in saline soil and help in promoting this plant's culture to provide food security under these perturbed global circumstances.

Transcriptome meta-analysis of abiotic stresses-responsive genes and identification of candidate transcription factors for broad stress tolerance in wheat.

Under field conditions, wheat is subjected to single or multiple stress conditions. The elucidation of the molecular mechanism of stress response is a key step to identify candidate genes for stress resistance in plants. In this study, RNA-seq data analysis identified 17.324, 10.562, 5.510, and 8.653 differentially expressed genes (DEGs) under salt, drought, heat, and cold stress, respectively. Moreover, the comparison of DEGs from each stress revealed 2374 shared genes from which 40% showed highly conserved expression patterns. Moreover, co-expression network analysis and GO enrichment revealed co-expression modules enriched with genes involved in transcription regulation, protein kinase pathway, and genes responding to phytohormones or modulating hormone levels. The expression of 15 selected transcription factor encoding genes was analyzed under abiotic stresses and ABA treatment in durum wheat. The identified transcription factor genes are excellent candidates for genetic engineering of stress tolerance in wheat.

Overexpression of durum wheat NAC transcription factor TtNTL3A promotes early flowering and increases multiple stress tolerance in transgenic Arabidopsis.

Plant-specific NAC transcription factors play important roles in plant development processes, hormone signaling and response to biotic and abiotic stresses. Here, a newly identified membrane-bound NAC gene, designated as TtNTL3A, was isolated from durum wheat. TtNTL3A was homologous to bread wheat TaNAC8 and rice OsNAC8. Moreover, yeast trans-activation assays revealed that TtNTL3A is a transcriptional activator. TtNTL3A was highly expressed in developing seeds and was induced by abiotic stresses, abscisic acid treatment and the infection with Fusarium graminearum. Besides, Transgenic Arabidopsis overexpressing TtNTL3A showed early flowering phenotype and higher tolerance to salt and drought stresses. RT-qPCR analysis revealed that drought and salt-responsive genes were highly expressed in transgenic lines compared to WT plants. Besides, these lines showed resistance to Fusarium graminearum, which was accompanied by a higher expression of pathogenesis-related genes (AtPR-1, Atpdf1.2, and AtNPR1) in TtNTL3A-OE lines. These findings suggest that TtNTL3A is an interesting target of genetic engineering to improve wheat tolerance to biotic and abiotic stresses.

Functional analysis of TmHKT1;4-A2 promoter through deletion analysis provides new insight into the regulatory mechanism underlying abiotic stress adaptation.

MAIN CONCLUSION: Bioinformatic, molecular, and biochemical analysis were performed to get more insight into the regulatory mechanism by which TmHKT1;4-A2 is regulated. HKT transporters from different plant species have been shown to play important role in plant response to salt. In previous work, TmHKT1;4-A2 gene from Triticum monococcum has been characterized as a major gene for Nax1 QTL (Tounsi et al. Plant Cell Physiol 57:2047-2057, 2016). So far, little is known about its regulatory mechanism. In this study, the promoter region of TmHKT1;4-A2 (1400 bp) was isolated and considered as the full-length promoter (PA2-1400). In silico analysis revealed the presence of important cis-acting elements related to abiotic stresses and phytohormones. Interestingly, our real-time RT-PCR analysis provided evidence that TmHKT1;4-A2 is regulated not only by salt stress but also by osmotic, heavy metal, oxidative, and hormones stresses. In transgenic Arabidopsis plants, TmHKT1;4-A2 is strongly active in vascular tissues of roots and leaves. Through 5'-end deletion analysis, we showed that PA2-1400 promoter is able to drive strong GUS activity under normal conditions and in response to different stresses compared to PA2-824 and PA2-366 promoters. These findings provide new information on the regulatory mechanism of TmHKT1;4-A2 and shed more light on its role under different stresses.

Highlight on the expression and the function of a novel MnSOD from diploid wheat (T. monococcum) in response to abiotic stress and heavy metal toxicity.

Superoxide dismutases (SODs) play a pivotal role in improving abiotic stress tolerance in plant cells. A novel manganese superoxide dismutase gene, denoted as TmMnSOD, was identified from Triticum monococcum. The encoded protein displayed high sequence identity with MnSOD family members and was highly homologous to TdMnSOD from durum wheat. Furthermore, the 3D structure analysis revealed that TmMnSOD displayed homotetramer subunit organization, incorporating four Mn2+ ions. Notably, TmMnSOD structure contains predominantly alpha helices with three beta sheets. On the other hand, under stress conditions, TmMnSOD transcript level was significantly up-regulated by salt, oxidative and heavy metal stresses. At the functional level, TmMnSOD imparts tolerance of yeast and E. coli cells under diverse stresses. Promoter analysis of TmMnSOD gene showed the presence of a great number of salt and pathogen-responsive cis-regulatory elements, highlighting the interest of this gene in breeding programs towards improved tolerance to salt stress in wheat.

Localization and expression analysis of a novel catalase from Triticum monococcum TmCAT1 involved in response to different environmental stresses.

Catalase proteins play a crucial role in detoxifying hydrogen peroxide, generated during plant growth, and in response to various environmental stresses. Despite their importance, little is known about their localization and expression in wheat. In this study, we identified and characterized a novel peroxisomal catalase gene from Triticum monococcum, designated as TmCAT1. Phylogenetic analysis revealed that TmCAT1 shared high identity with TdCAT1 and other plant catalases belonging to subfamily 1. We predicted the 3D structure model and the oligomerization arrangement of TmCAT1. Besides, we displayed an arrangement in asymmetric unit, which involved interactions including, mainly, residues from N-terminal domain. Interestingly, sequence analysis indicated that TmCAT1, like TdCAT1, had the peroxisomal targeting signal (PTS1) around its C-terminus. Transient expression of TmCAT1-GFP and TdCAT1-GFP in tobacco leaves revealed that the two fused proteins are targeted into peroxisomes. However, the truncated forms lacking the tripeptide QKL remained in the cytosol. Concerning the expression profile analysis, TmCAT1 is expressed especially in leaves in normal condition. On the other hand, it is up-regulated by different stress incorporating salt, osmotic, oxidative, heavy metal and hormones stresses. Functional analysis by heterologous expression in yeast cells showed that TmCAT1 improved tolerance to multiple abiotic stresses. The presence of important cis-regulatory elements in the promoter region of TmCAT1 strongly reinforces the interest of this gene in plant adaptation to various stresses.

Promoter of the TmHKT1;4-A1 gene of Triticum monococcum directs stress inducible, developmental regulated and organ specific gene expression in transgenic Arbidopsis thaliana.

HKT transporters which mediate Na+-specific transport or Na+-K+ co-transport, play an important role in protecting plants from salinity stress by preventing Na+-over-accumulation in leaves. In this work, a 1508-bp genomic fragment upstream of the TmHKT1;4-A1 translated sequence from Triticum monococcum has been isolated, cloned, and designated as the ''PrTmHKT1;4-A1'' promoter. Sequence analysis of ''PrTmHKT1;4-A1'' revealed the presence of cis-regulatory elements which could be required for abiotic stress and abscisic acid (ABA) responsiveness. The PrTmHKT1;4-A1 sequence was fused to the ß-glucuronidase gene and the resulting construct was transferred into Arabidopsis plants. Histochemical assays of stably transformed Arabidopsis plants showed that PrTmHKT1;4-A1 is active in this heterologous system. Under control conditions, GUS histochemical staining was observed significantly only in leaves of 20-day-old plants. Histological sections prepared at this stage and in leaves revealed activity localized in leaf veins (phloem and bundle sheath). In flowers, GUS activity was detected only in sepals. After 3 days of challenging the plants with salt, dehydration or ABA treatments, the PrTmHKT1;4-A1 transformed Arabidopsis plants showed a substantial increase in the GUS staining in leaves, compared to untransformed plants under the same conditions. Real time qPCR expression analysis of the uidA gene, showed that GusA transcripts were up-regulated by salt, dehydration, and ABA treatments. All together, these results showed that PrTmHKT1;4-A1 is an age-dependent, abiotic-stress-inducible, organ-specific and tissue-specific promoter in a heterologous dicot system.

Genome-wide analysis and expression profiling of the ERF transcription factor family in potato (Solanum tuberosum L.).

The ERF transcription factors belong to the AP2/ERF superfamily, one of the largest transcription factor families in plants. They play important roles in plant development processes, as well as in the response to biotic, abiotic, and hormone signaling. In the present study, 155 putative ERF transcription factor genes were identified from the potato (Solanum tuberosum) genome database, and compared with those from Arabidopsis thaliana. The StERF proteins are divided into ten phylogenetic groups. Expression analyses of five StERFs were carried out by semi-quantitative RT-PCR and compared with published RNA-seq data. These latter analyses were used to distinguish tissue-specific, biotic, and abiotic stress genes as well as hormone-responsive StERF genes. The results are of interest to better understand the role of the AP2/ERF genes in response to diverse types of stress in potatoes. A comprehensive analysis of the physiological functions and biological roles of the ERF family genes in S. tuberosum is required to understand crop stress tolerance mechanisms.

PVY-resistant transgenic potato plants expressing an anti-NIa protein scFv antibody.

A synthetic gene encoding a single chain Fv fragment of an antibody directed against the nuclear inclusion a (NIa) protein of potato virus Y (PVY) was used to transform two commercial potato cultivars (Claustar and BF15). The NIa protease forms the nuclear inclusion body A and acts as the major protease in the cleavage of the viral polyprotein into functional proteins. Immunoblot analysis showed that most of the resulting transgenic plants accumulate high levels of the transgenic protein. Furthermore, a majority of the selected transgenic lines showed an efficient and complete protection against the challenge virus after mechanical inoculation with PVYO strain. Two transgenic lines showed an incomplete resistance with delayed appearance of symptoms accompanied by low virus titers, whereas one line developed symptoms during the first days after inoculation but recovered rapidly, leading to a low virus accumulation rate. These results confirm that expression of scFv antibody is able to inhibit a crucial step in the virus multiplication, such as polyprotein cleavage is a powerful strategy for engineered virus resistance. It can lead to a complete resistance that was not obtained previously by expression of scFv directed against the viral coat protein.