Superoxide dismutase (SOD) family in durum wheat: promising candidates for improving crop resilience

Decoding the role of durum wheat ascorbate peroxidase TdAPX7B-2 in abiotic stress response

APX proteins are H2O2-scavenging enzymes induced during oxidative stress. In the first part of this study, we provided an extensive knowledge on the APX family of Triticum durum, TdAPX and their related TdAPX-R, via the genome wide analysis. The outcomes showed that these proteins are clustered into four major subgroups. Furthermore, the exon-intron structure and the synteny analyses revealed that during evolution the genes TdAPX and TdAPX-R are relatively conserved. Besides, during their evolution, these genes underwent purifying selection pressure and were duplicated in segmental. In parallel, the analysis of the conserved motifs and the multiple sequence alignment demonstrated that the residues involved in the active sites, heme- and cations-binding are conserved only in TdAPX proteins. Following the RNA-seq data and the regulatory elements analyses, we focused in the second part of this study on the functional characterization of TdAPX7B-2. The qRT-PCR data showed the upregulation of TdAPX7B-2 essentially in leaves of durum wheat exposed to salt, cold, drought, metals and ABA treatments. The tolerance phenotype of the TdAPX7B-2-expressing Arabidopsis lines to salt, direct-induced oxidative stress and heavy metals was manifested by the development of root system, proline accumulation and induction of the antioxidant CAT, SOD and POD enzymes to maintain the non-toxic H2O2 levels. Likewise, the response to salt stress and direct-oxidative stress of the transgenic lines was accompanied mainly by the induction of AtNCED3, AtRD29A/B and AtERD1.

Coping with salinity stress: segmental group 7 chromosome introgressions from halophytic Thinopyrum species greatly enhance tolerance of recipient durum wheat

Increased soil salinization, tightly related to global warming and drought and exacerbated by intensified irrigation supply, implies highly detrimental effects on staple food crops such as wheat. The situation is particularly alarming for durum wheat (DW), better adapted to arid/semi-arid environments yet more sensitive to salt stress than bread wheat (BW). To enhance DW salinity tolerance, we resorted to chromosomally engineered materials with introgressions from allied halophytic Thinopyrum species. "Primary" recombinant lines (RLs), having portions of their 7AL arms distally replaced by 7el1L Th. ponticum segments, and "secondary" RLs, harboring Th. elongatum 7EL insertions "nested" into 7el1L segments, in addition to near-isogenic lines lacking any alien segment (CLs), cv. Om Rabia (OR) as salt tolerant control, and BW introgression lines with either most of 7el1 or the complete 7E chromosome substitution as additional CLs, were subjected to moderate (100 mM) and intense (200 mM) salt (NaCl) stress at early growth stages. The applied stress altered cell cycle progression, determining a general increase of cells in G1 and a reduction in S phase. Assessment of morpho-physiological and biochemical traits overall showed that the presence of Thinopyrum spp. segments was associated with considerably increased salinity tolerance versus its absence. For relative water content, Na+ accumulation and K+ retention in roots and leaves, oxidative stress indicators (malondialdehyde and hydrogen peroxide) and antioxidant enzyme activities, the observed differences between stressed and unstressed RLs versus CLs was of similar magnitude in "primary" and "secondary" types, suggesting that tolerance factors might reside in defined 7el1L shared portion(s). Nonetheless, the incremental contribution of 7EL segments emerged in various instances, greatly mitigating the effects of salt stress on root and leaf growth and on the quantity of photosynthetic pigments, boosting accumulation of compatible solutes and minimizing the decrease of a powerful antioxidant like ascorbate. The seemingly synergistic effect of 7el1L + 7EL segments/genes made "secondary" RLs able to often exceed cv. OR and equal or better perform than BW lines. Thus, transfer of a suite of genes from halophytic germplasm by use of fine chromosome engineering strategies may well be the way forward to enhance salinity tolerance of glycophytes, even the sensitive DW.

Identification and characterization of the critical genes encoding Cd-induced enhancement of SOD isozymes activities in Zhe-Maidong (Ophiopogon japonicus)

Superoxide dismutase (SOD) protects plants from abiotic stress-induced reactive oxygen species (ROS) damage. Here, the effects of cadmium (Cd) exposure on ROS accumulation and SOD isozymes, as well as the identification of significant SOD isozyme genes, were investigated under different Cd stress treatments to Zhe-Maidong (Ophiopogon japonicus). The exposure to Cd stress resulted in a notable elevation in the SOD activity in roots. Cu/ZnSODa and Cu/ZnSODb were the most critical SOD isozymes in response to Cd stress, as indicated by the detection results for SOD isozymes. A total of 22 OjSOD genes were identified and classified into three subgroups, including 10 OjCu/ZnSODs, 6 OjMnSODs, and 6 OjFeSODs, based on the analysis of conserved motif and phylogenetic tree. Cu/ZnSOD-15, Cu/ZnSOD-18, Cu/ZnSOD-20, and Cu/ZnSOD-22 were the main genes that control the increase in SOD activity under Cd stress, as revealed via quantitative PCR and transcriptome analysis. Additionally, under various heavy metal stress (Cu2+, Fe2+, Zn2+, Mn2+), Cu/ZnSOD-15, Cu/ZnSOD-18, and Cu/ZnSOD-22 gene expression were significantly upregulated, indicating that these three genes play a critical part in resisting heavy metal stress. The molecular docking experiments performed on the interaction between oxygen ion (O2•-) and OjSOD protein have revealed that the critical amino acid residues involved in the binding of Cu/ZnSOD-22 to the substrate were Pro135, Ile136, Ile140, and Arg144. Our findings provide a solid foundation for additional functional investigations on the OjSOD genes, as well as suggestions for improving genetic breeding and agricultural management strategies to increase Cd resistance in O. japonicus.

The thioredoxin h-type TdTrxh2 protein of durum wheat confers abiotic stress tolerance of the transformant Arabidopsis plants through its protective role and the regulation of redox homoeostasis

The thioredoxins (Trxs) are ubiquitous and they play a crucial role in various biological processes like growth and stress response. Although the functions of Trxs proteins are described in several previous reports, the function of the isoform Trxh2 of durum wheat (Triticum durum L.), designated as TdTrxh2, in abiotic stress response still unknown. Thus, we aimed in this study the functional characterization of TdTrxh2 through its expression in yeast cells and Arabidopsis plants. Sequence analysis revealed that TdTrxh2 protein shared the conserved redox site with the other Trxh from other plant species. Under various abiotic stresses, TdTrxh2 was up-regulated in leaves and roots of durum wheat. Interestingly, we demonstrated that TdTrxh2 exhibit protective effect on LDH activity against various treatments. Besides, the expression of TdTrxh2 in yeast cells conferred their tolerance to multiple stresses. Moreover, transgenic Arabidopsis expressing TdTrxh2 showed tolerance phenotype to several abiotic stresses. This tolerance was illustrated by high rate of proline accumulation, root proliferation, low accumulation of reactive oxygen species like H2O2 and O2·-, and high antioxidant CAT and POD enzymes activities. All these findings suggested that TdTrxh2 promotes abiotic stress tolerance through the redox homoeostasis regulation and its protective role.

Genome-Wide Analysis of Strictosidine Synthase-like Gene Family Revealed Their Response to Biotic/Abiotic Stress in Poplar

The strictosidine synthase-like (SSL) gene family is a small plant immune-regulated gene family that plays a critical role in plant resistance to biotic/abiotic stresses. To date, very little has been reported on the SSL gene in plants. In this study, a total of thirteen SSLs genes were identified from poplar, and these were classified into four subgroups based on multiple sequence alignment and phylogenetic tree analysis, and members of the same subgroup were found to have similar gene structures and motifs. The results of the collinearity analysis showed that poplar SSLs had more collinear genes in the woody plants Salix purpurea and Eucalyptus grandis. The promoter analysis revealed that the promoter region of PtrSSLs contains a large number of biotic/abiotic stress response elements. Subsequently, we examined the expression patterns of PtrSSLs following drought, salt, and leaf blight stress, using RT-qPCR to validate the response of PtrSSLs to biotic/abiotic stresses. In addition, the prediction of transcription factor (TF) regulatory networks identified several TFs, such as ATMYB46, ATMYB15, AGL20, STOP1, ATWRKY65, and so on, that may be induced in the expression of PtrSSLs in response to adversity stress. In conclusion, this study provides a solid basis for a functional analysis of the SSL gene family in response to biotic/abiotic stresses in poplar.

Metabolism and Signaling of Plant Mitochondria in Adaptation to Environmental Stresses

The interaction of mitochondria with cellular components evolved differently in plants and mammals; in plants, the organelle contains proteins such as ALTERNATIVE OXIDASES (AOXs), which, in conjunction with internal and external ALTERNATIVE NAD(P)H DEHYDROGENASES, allow canonical oxidative phosphorylation (OXPHOS) to be bypassed. Plant mitochondria also contain UNCOUPLING PROTEINS (UCPs) that bypass OXPHOS. Recent work revealed that OXPHOS bypass performed by AOXs and UCPs is linked with new mechanisms of mitochondrial retrograde signaling. AOX is functionally associated with the NO APICAL MERISTEM transcription factors, which mediate mitochondrial retrograde signaling, while UCP1 can regulate the plant oxygen-sensing mechanism via the PRT6 N-Degron. Here, we discuss the crosstalk or the independent action of AOXs and UCPs on mitochondrial retrograde signaling associated with abiotic stress responses. We also discuss how mitochondrial function and retrograde signaling mechanisms affect chloroplast function. Additionally, we discuss how mitochondrial inner membrane transporters can mediate mitochondrial communication with other organelles. Lastly, we review how mitochondrial metabolism can be used to improve crop resilience to environmental stresses. In this respect, we particularly focus on the contribution of Brazilian research groups to advances in the topic of mitochondrial metabolism and signaling.