Prediction and verification of microRNAs related to proline accumulation under drought stress in potato

Deciphering Drought Resilience in Solanaceae Crops: Unraveling Molecular and Genetic Mechanisms

The Solanaceae family, which includes vital crops such as tomatoes, peppers, eggplants, and potatoes, is increasingly impacted by drought due to climate change. Recent research has concentrated on unraveling the molecular mechanisms behind drought resistance in these crops, with a focus on abscisic acid (ABA) signaling pathways, transcription factors (TFs) like MYB (Myeloblastosis), WRKY (WRKY DNA-binding protein), and NAC (NAM, ATAF1/2, and CUC2- NAM: No Apical Meristem, ATAF1/2, and CUC2: Cup-shaped Cotyledon), and the omics approaches. Moreover, transcriptome sequencing (RNA-seq) has been instrumental in identifying differentially expressed genes (DEGs) crucial for drought adaptation. Proteomics studies further reveal changes in protein expression under drought conditions, elucidating stress response mechanisms. Additionally, microRNAs (miRNAs) have been identified as key regulators in drought response. Advances in proteomics and transcriptomics have highlighted key proteins and genes that respond to drought stress, offering new insights into drought tolerance. To address the challenge of drought, future research should emphasize the development of drought-resistant varieties through precision breeding techniques such as gene editing, marker-assisted selection (MAS), and the integration of artificial intelligence. Additionally, the adoption of environmentally sustainable cultivation practices, including precision irrigation and the use of anti-drought agents, is crucial for improving water-use efficiency and crop resilience. International collaboration and data sharing will be essential to accelerate progress and ensure global food security in increasingly arid conditions. These efforts will enable Solanaceae crops to adapt the challenges posed by climate change, ensuring their productivity and sustainability.

DRB1, DRB2 and DRB4 Are Required for an Appropriate miRNA-Mediated Molecular Response to Osmotic Stress in Arabidopsis thaliana

Arabidopsis thaliana (Arabidopsis) double-stranded RNA binding (DRB) proteins DRB1, DRB2 and DRB4 perform essential roles in microRNA (miRNA) production, with many of the produced miRNAs mediating aspects of the molecular response of Arabidopsis to abiotic stress. Exposure of the drb1, drb2 and drb4 mutants to mannitol stress showed drb2 to be the most sensitive to this form of osmotic stress. Profiling of the miRNA landscapes of mannitol-stressed drb1, drb2 and drb4 seedlings via small RNA sequencing, and comparison of these to the profile of mannitol-stressed wild-type Arabidopsis plants, revealed that the ability of the drb1 and drb2 mutants to mount an appropriate miRNA-mediated molecular response to mannitol stress was defective. RT-qPCR was next used to further characterize seven miRNA/target gene expression modules, with this analysis identifying DRB1 as the primary DRB protein required for miR160, miR164, miR167 and miR396 production. In addition, via its antagonism of DRB1 function, DRB2 was shown by RT-qPCR to play a secondary role in regulating the production of these four miRNAs. This analysis further showed that DRB1, DRB2 and DRB4 are all required to regulate the production of miR399 and miR408, and that DRB4 is the primary DRB protein required to produce the non-conserved miRNA, miR858. Finally, RT-qPCR was used to reveal that each of the seven characterized miRNA/target gene expression modules responded differently to mannitol-induced osmotic stress in each of the four assessed Arabidopsis lines. In summary, this research has identified mannitol-stress-responsive miRNA/target gene expression modules that can be molecularly manipulated in the future to generate novel Arabidopsis lines with increased tolerance to this form of osmotic stress.

MYB transcription factors, their regulation and interactions with non-coding RNAs during drought stress in Brassica juncea

BACKGROUND

Brassica juncea (L.) Czern is an important oilseed crop affected by various abiotic stresses like drought, heat, and salt. These stresses have detrimental effects on the crop's overall growth, development and yield. Various Transcription factors (TFs) are involved in regulation of plant stress response by modulating expression of stress-responsive genes. The myeloblastosis (MYB) TFs is one of the largest families of TFs associated with various developmental and biological processes such as plant growth, secondary metabolism, stress response etc. However, MYB TFs and their regulation by non-coding RNAs (ncRNAs) in response to stress have not been studied in B. juncea. Thus, we performed a detailed study on the MYB TF family and their interactions with miRNAs and Long non coding RNAs.

RESULTS

Computational investigation of genome and proteome data presented a comprehensive picture of the MYB genes and their protein architecture, including intron-exon organisation, conserved motif analysis, R2R3 MYB DNA-binding domains analysis, sub-cellular localization, protein-protein interaction and chromosomal locations. Phylogenetically, BjuMYBs were further classified into different subclades on the basis of topology and classification in Arabidopsis. A total of 751 MYBs were identified in B. juncea corresponding to 297 1R-BjuMYBs, 440 R2R3-BjuMYBs, 12 3R-BjuMYBs, and 2 4R-BjuMYBs types. We validated the transcriptional profiles of nine selected BjuMYBs under drought stress through RT-qPCR. Promoter analysis indicated the presence of drought-responsive cis-regulatory components. Additionally, the miRNA-MYB TF interactions was also studied, and most of the microRNAs (miRNAs) that target BjuMYBs were involved in abiotic stress response and developmental processes. Regulatory network analysis and expression patterns of lncRNA-miRNA-MYB indicated that selected long non-coding RNAs (lncRNAs) acted as strong endogenous target mimics (eTMs) of the miRNAs regulated expression of BjuMYBs under drought stress.

CONCLUSIONS

The present study has established preliminary groundwork of MYB TFs and their interaction with ncRNAs in B. juncea and it will help in developing drought- tolerant Brassica crops.

miRNA Sequencing Analysis in Maize Roots Treated with Neutral and Alkaline Salts

Soil salinization/alkalization is a complex environmental factor that includes not only neutral salt NaCl but also other components like Na2CO3. miRNAs, as small molecules that regulate gene expression post-transcriptionally, are involved in plant responses to abiotic stress. In this study, maize seedling roots were treated for 5 h with 100 mM NaCl, 50 mM Na2CO3, and H2O, respectively. Sequencing analysis of differentially expressed miRNAs under these conditions revealed that the Na2CO3 treatment group had the most differentially expressed miRNAs. Cluster analysis indicated their main involvement in the regulation of ion transport, binding, metabolism, and phenylpropanoid and flavonoid biosynthesis pathways. The unique differentially expressed miRNAs in the NaCl treatment group were related to the sulfur metabolism pathway. This indicates a significant difference in the response patterns of maize to different treatment groups. This study provides theoretical evidence and genetic resources for further analysis of the molecular mechanisms behind maize's salt-alkali tolerance.

Comprehensive investigation of cucumber heat shock proteins under abiotic stress conditions: A multi-omics survey

Heat-shock proteins (Hsps) are a family of proteins essential in preserving the vitality and functionality of proteins under stress conditions. Cucumber (Cucumis sativus) is a widely grown plant with high nutritional value and is used as a model organism in many studies. This study employed a genomics, transcriptomics, and metabolomics approach to investigate cucumbers' Hsps against abiotic stress conditions. Bioinformatics methods were used to identify six Hsp families in the cucumber genome and to characterize family members. Transcriptomics data from the Sequence Read Archive (SRA) database was also conducted to select CsHsp genes for further study. Real-time PCR was used to evaluate gene expression levels under different stress conditions, revealing that CssHsp-08 was a vital gene for resistance to stress conditions; including drought, salinity, cold, heat stresses, and ABA application. Gas Chromatography-Mass Spectrometry (GC-MS) analysis of plant extracts revealed that amino acids accumulate in leaves under high temperatures and roots under drought, while sucrose accumulates in both tissues under applied most stress factors. The study provides valuable insights into the structure, organization, evolution, and expression profiles of the Hsp family and contributes to a better understanding of plant stress mechanisms. These findings have important implications for developing crops that can withstand environmental stress conditions better.

Screening of differentially expressed microRNAs and target genes in two potato varieties under nitrogen stress

BACKGROUND

A reasonable supply of nitrogen (N) fertilizer is essential for obtaining high-quality, high-level, and stable potato yields, and an improvement in the N utilization efficiency can effectively reduce N fertilizer use. It is important to use accurate, straightforward, and efficient transgenic breeding techniques for the identification of genes that can improve nitrogen use efficiency, thus enabling us to achieve the ultimate goal of breeding N-efficient potato varieties. In recent years, some of the mechanisms of miRNAs have been elucidated via the analysis of the correlation between the expression levels of potato miRNA target genes and regulated genes under conditions of stress, but the role of miRNAs in the inhibition/expression of key genes regulating N metabolism under N stress is still unclear. Our study aimed to identify the role played by specific enzymes and miRNAs in the responses of plants to N stress.

RESULTS

The roots and leaves of the N-efficient potato variety, Yanshu4 ("Y"), and N-inefficient potato variety, Atlantic ("D"), were collected at the seedling and budding stages after they were exposed to different N fertilizer treatments. The miRNAs expressed differentially under the two types of N stress and their corresponding target genes were first predicted using miRNA and degradome analysis. Then, quantitative polymerase chain reaction (qRT-PCR) was performed to verify the expression of differential miRNAs that were closely related to N metabolism. Finally, the shearing relationship between stu-miR396-5p and its target gene StNiR was determined by analyzing luciferase activity levels. The results showed that NiR activity increased significantly with an increase in the applied N levels from the seedling stage to the budding stage, and NiR responded significantly to different N treatments. miRNA sequencing enabled us to predict 48 families with conserved miRNAs that were mainly involved in N metabolism, carbon metabolism, and amino acid biosynthesis. The differences in the expression of the following miRNAs were identified via screening (high expression levels and P < 0.05): stu-miR396-5p, stu-miR408b-3p_R-1, stu-miR3627-3p, stu-miR482a-3p, stu-miR8036-3p, stu-miR482a-5p, stu-miR827-5p, stu-miR156a_L-1, stu-miR827-3p, stu-miR172b-5p, stu-miR6022-p3_7, stu-miR398a-5p, and stu-miR166c-5p_L-3. Degradome analysis showed that most miRNAs had many-to-many relationships with target genes. The main target genes involved in N metabolism were NiR, NiR1, NRT2.5, and NRT2.7. qRT-PCR analysis showed that there were significant differences in the expression levels of stu-miR396-5p, stu-miR8036-3p, and stu-miR482a-3p in the leaves and roots of the Yanshu4 and Atlantic varieties at the seedling and budding stages under conditions that involved no N and excessive N application; the expression of these miRNAs was induced in response to N stress. The correlation between the differential expression of stu-miR396-5p and its corresponding target gene NiR was further verified by determining the luciferase activity level and was found to be strongly negative.

CONCLUSION

The activity of NiR was significantly positively correlated with N application from the seedling to the budding stage. Differential miRNAs and target genes showed a many-to-many relationship with each other. The expression of stu-miR396-5p, stu-miR482a-3p, and stu-miR8036-3p in the roots and leaves of the Yanshu4 and Atlantic varieties at the seedling and budding stages was notably different under two types of N stress. Under two types of N stress, stu-miR396-5p was down-regulated in Yanshu4 in the seedling-stage and shoot-stage roots, and up-regulated in seedling-stage roots and shoot-stage leaves; stu-miR482a-3p was up-regulated in the seedling and shoot stages. The expression of stu-miR8036-3p was up-regulated in the leaves and roots at the seedling and budding stages, and down-regulated in roots under both types of N stress. The gene expressing the key enzyme involved in N metabolism, StNiR, and the stu-miR396-5p luciferase assay reporter gene had a strong regulatory relationship with each other. This study provides candidate miRNAs related to nitrogen metabolism and highlights that differential miRNAs play a key role in nitrogen stress in potato, providing insights for future research on miRNAs and their target genes in nitrogen metabolic pathways and breeding nitrogen-efficient potatoes.

Effects of Dark Septate Endophytes on the Performance and Soil Microbia of Lycium ruthenicum Under Drought Stress

In the current study, we explored the effects of dark septate endophytes (DSE) (Neocamarosporium phragmitis, Alternaria chlamydospore, and Microascus alveolaris) on the performance and rhizosphere soil microbial composition of Lycium ruthenicum Murr under drought stress. Differences in plant growth and physiological indexes, soil parameters, and microbial composition under different treatments were studied. Three DSE species could form good symbiotic relationships with L. ruthenicum plants, and the symbionts depended on DSE species and water availability. Inoculation of DSE had the greatest benefit on host plants under drought conditions. In particular, N. phragmitis and A. chlamydospore had a significant positive influence on the biomass, morphological and physiological indexes of host plants. Additionally, the content of arbuscular mycorrhiza (AM) fungi, gram-negative bacteria, and actinomycetes in the soil was significantly elevated after DSE inoculation in the absence of water. Based on a variance decomposition analysis, DSE was the most important factor affecting the growth and physiological parameters of host plants, and DSE inoculation combined with water conditions significantly affected the contents of soil microbial communities. Structural equation model (SEM) analysis showed that the positive effects of DSE on L. ruthenicum varied with DSE species and plant parameters under different water conditions. These results are helpful to understand the ecological function of DSE and its potential application in the cultivation of L. ruthenicum plants in drylands.

Research on lncRNA related to drought resistance of Shanlan upland rice

Background

Drought has become the major abiotic stress that causes losses in rice yields and consequently is one of the main environmental factors threatening food security. Long non-coding RNA (lncRNA) is known to play an important role in plant response to drought stress, while the mechanisms of competing endogenous RNA (ceRNA) in drought resistance in upland rice have been rarely reported.

Results

In our study, a total of 191 lncRNAs, 2115 mRNAs and 32 miRNAs (microRNAs) were found by strand-specific sequencing and small RNA sequencing to be differentially expressed in drought-stressed rice. Functional analysis of results indicate that they play important roles in hormone signal transduction, chlorophyll synthesis, protein synthesis and other pathways. Construction of a ceRNA network revealed that MSTRG.28732.3 may interact with miR171 in the chlorophyll biosynthesis pathway and affect the ability of plants to withstand drought stress by regulating Os02g0662700, Os02g0663100 and Os06g0105350. The accuracy of the regulatory network was verified by qRT-PCR.

Conclusion

Our results provide a theoretical basis for future studies on the potential function of lncRNA in plant drought resistance, and they provide new genetic resources for drought-resistant rice breeding.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08546-0.

Arbuscular Mycorrhizae Mitigate Aluminum Toxicity and Regulate Proline Metabolism in Plants Grown in Acidic Soil

Arbuscular mycorrhizal fungi (AMF) can promote plant growth and induce stress tolerance. Proline is reported to accumulate in mycorrhizal plants under stressful conditions, such as aluminum (Al) stress. However, the detailed changes induced in proline metabolism under AMF–plant symbiosis has not been studied. Accordingly, this work aimed to study how Al-stressed grass (barley) and legume (lotus) species respond to AMF inoculation at growth and biochemical levels. The associated changes in Al uptake and accumulation, the rate of photosynthesis, and the key enzymes and metabolites involved in proline biosynthesis and degradation pathways were studied. Soil contamination with Al induced Al accumulation in tissues of both species and, consequently, reduced plant growth and the rate of photosynthesis, while more tolerance was noticed in lotus. Inoculation with AMF significantly reduced Al accumulation and mitigated the negative impacts of Al on growth and photosynthesis in both species; however, these positive effects were more pronounced in barley plants. The mitigating action of AMF was associated with upregulation of proline biosynthesis through glutamate and ornithine pathways, more in lotus than in barley, and repression of its catabolism. The increased proline level in lotus was consistent with improved N metabolism (N level and nitrate reductase). Overall, this study suggests the role of AMF in mitigating Al stress, where regulation of proline metabolism is a worthy mechanism underlying this mitigating action.

MicroRNAs: Potential Targets for Developing Stress-Tolerant Crops

Crop yield is challenged every year worldwide by changing climatic conditions. The forecasted climatic scenario urgently demands stress-tolerant crop varieties to feed the ever-increasing global population. Molecular breeding and genetic engineering approaches have been frequently exploited for developing crops with desired agronomic traits. Recently, microRNAs (miRNAs) have emerged as powerful molecules, which potentially serve as expression markers during stress conditions. The miRNAs are small non-coding endogenous RNAs, usually 20-24 nucleotides long, which mediate post-transcriptional gene silencing and fine-tune the regulation of many abiotic- and biotic-stress responsive genes in plants. The miRNAs usually function by specifically pairing with the target mRNAs, inducing their cleavage or repressing their translation. This review focuses on the exploration of the functional role of miRNAs in regulating plant responses to abiotic and biotic stresses. Moreover, a methodology is also discussed to mine stress-responsive miRNAs from the enormous amount of transcriptome data available in the public domain generated using next-generation sequencing (NGS). Considering the functional role of miRNAs in mediating stress responses, these molecules may be explored as novel targets for engineering stress-tolerant crop varieties.

Genome-Wide Characterization, Evolution, and Expression Profile Analysis of GATA Transcription Factors in Brachypodium distachyon

The GATA proteins, functioning as transcription factors (TFs), are involved in multiple plant physiological and biochemical processes. In this study, 28 GATA TFs of Brachypodium distachyon (BdGATA) were systematically characterized via whole-genome analysis. BdGATA genes unevenly distribute on five chromosomes of B. distachyon and undergo purifying selection during the evolution process. The putative cis-acting regulatory elements and gene interaction network of BdGATA were found to be associated with hormones and defense responses. Noticeably, the expression profiles measured by quantitative real-time PCR indicated that BdGATA genes were sensitive to methyl jasmonate (MeJA) and salicylic acid (SA) treatment, and 10 of them responded to invasion of the fungal pathogen Magnaporthe oryzae, which causes rice blast disease. Genome-wide characterization, evolution, and expression profile analysis of BdGATA genes can open new avenues for uncovering the functions of the GATA genes family in plants and further improve the knowledge of cellular signaling in plant defense.

Temporal dynamics of QTL effects on vegetative growth in Arabidopsis thaliana

We assessed early vegetative growth in a population of 382 accessions of Arabidopsis thaliana using automated non-invasive high-throughput phenotyping. All accessions were imaged daily from 7 d to 18 d after sowing in three independent experiments and genotyped using the Affymetrix 250k SNP array. Projected leaf area (PLA) was derived from image analysis and used to calculate relative growth rates (RGRs). In addition, initial seed size was determined. The generated datasets were used jointly for a genome-wide association study that identified 238 marker-trait associations (MTAs) individually explaining up to 8% of the total phenotypic variation. Co-localization of MTAs occurred at 33 genomic positions. At 21 of these positions, sequential co-localization of MTAs for 2-9 consecutive days was observed. The detected MTAs for PLA and RGR could be grouped according to their temporal expression patterns, emphasizing that temporal variation of MTA action can be observed even during the vegetative growth phase, a period of continuous formation and enlargement of seemingly similar rosette leaves. This indicates that causal genes may be differentially expressed in successive periods. Analyses of the temporal dynamics of biological processes are needed to gain important insight into the molecular mechanisms of growth-controlling processes in plants.

Identification of watermelon heat shock protein members and tissue-specific gene expression analysis under combined drought and heat stresses

Heat shock protein (Hsp) gene family members in the watermelon genome were identified and characterized by bioinformatics analysis. In addition, expression profiles of genes under combined drought and heat stress conditions were experimentally analyzed. In the watermelon genome, 39 genes belonging to the sHsp family, 101 genes belonging to the Hsp40 family, 23 genes belonging to the Hsp60 family, 12 genes belonging to the Hsp70 family, 6 genes belonging to the Hsp90 family, and 102 genes belonging to the Hsp100 family were found. It was also observed that the proteins in the same cluster in the phylogenetic trees had similar motif patterns. When the estimated 3-dimensional structures of the Hsp proteins were examined, it was determined that the α-helical structure was dominant in almost all families. The most orthologous relationship appeared to be between watermelon, soybean, and poplar in the ClaHsp gene families. For tissue-specific gene expression analysis under combined stress conditions, expression analysis of one representative Hsp gene each from root, stem, leaf, and shoot tissues was performed by real-time PCR. A significant increase was detected usually at 30 min in almost all tissues. This study provides extensive information for watermelon Hsps, and can enhance our knowledge about the relationships between Hsp genes and combined stresses.

Identification of miRNAs linked with the drought response of tef [Eragrostis tef (Zucc.) Trotter]

Tef [Eragrostis tef (Zucc.) Trotter], a staple food crop in the Horn of Africa and particularly in Ethiopia, has several beneficial agronomical and nutritional properties, including waterlogging and drought tolerance. In this study, we performed microRNA profiling of tef using the Illumina HiSeq 2500 platform, analyzing both shoots and roots of two tef genotypes, one drought-tolerant (Tsedey) and one drought-susceptible (Alba). We obtained more than 10 million filtered reads for each of the 24 sequenced small cDNA libraries. Reads mapping to known miRNAs were more abundant in the root than shoot tissues. Thirteen and 35 miRNAs were significantly modulated in response to drought, in Alba and Tsedey roots, respectively. One miRNA was upregulated under drought conditions in both genotypes. In shoots, nine miRNAs were modulated in common between the two genotypes and all showed similar trends of expression. One-hundred and forty-seven new miRNA mature sequences were identified in silico, 22 of these were detected in all relevant samples and seven were differentially regulated when comparing drought with normal watering. Putative targets of the miRNA regulated under drought in root and shoot tissues were predicted. Among the targets were transcription factors such as CCAAT-HAP2, MADS and NAC. Verification with qRT-PCR revealed that five of six potential targets showed a pattern of expression that was consistent with the correspondent miRNA amount measured by RNA-Seq. In general, candidate miRNAs involved in the post-transcriptional regulation of the tef response to drought could be included in next-generation breeding programs.

MicroRNAs associated with drought response in the pulse crop common bean (Phaseolus vulgaris L.)

Drought stress significantly reduces common bean yields. Recently, some drought-related miRNAs were found in various plants. However, reports of miRNAs involved in drought stress in common bean are limited. Here, we obtained four sRNA samples from drought-tolerant and -sensitive cultivars of common bean that experienced with or without drought treatment. A total of 49 novel miRNAs and 120 known miRNAs were detected. Under drought treatment, 9 and 7 known miRNAs were down and up-regulated, respectively, and 5 and 3 of the novel miRNAs were increased and decreased, respectively. Among these miRNAs, four miRNAs shared the same pattern of expression between Long 22-0579 and Naihua. Target genes of these miRNAs included transcription factors, protein kinases, and nuclear transcription factors. Finally, we verified all of the differentially expressed miRNAs by RT-qPCR, and we identified 16 miRNAs that are potentially associated with the drought stress response. These miRNAs and target genes will be useful in future basic studies and in applied studies investigating how miRNA regulation can be used to enhance drought resistance in plant species.

Identification and Characterization of Small Noncoding RNAs in Genome Sequences of the Edible Fungus Pleurotus ostreatus

Noncoding RNAs (ncRNAs) have been identified in many fungi. However, no genome-scale identification of ncRNAs has been inventoried for basidiomycetes. In this research, we detected 254 small noncoding RNAs (sncRNAs) in a genome assembly of an isolate (CCEF00389) of Pleurotus ostreatus, which is a widely cultivated edible basidiomycetous fungus worldwide. The identified sncRNAs include snRNAs, snoRNAs, tRNAs, and miRNAs. SnRNA U1 was not found in CCEF00389 genome assembly and some other basidiomycetous genomes by BLASTn. This implies that if snRNA U1 of basidiomycetes exists, it has a sequence that varies significantly from other organisms. By analyzing the distribution of sncRNA loci, we found that snRNAs and most tRNAs (88.6%) were located in pseudo-UTR regions, while miRNAs are commonly found in introns. To analyze the evolutionary conservation of the sncRNAs in P. ostreatus, we aligned all 254 sncRNAs to the genome assemblies of some other Agaricomycotina fungi. The results suggest that most sncRNAs (77.56%) were highly conserved in P. ostreatus, and 20% were conserved in Agaricomycotina fungi. These findings indicate that most sncRNAs of P. ostreatus were not conserved across Agaricomycotina fungi.

Hexaconazole-Cu complex improves the salt tolerance of Triticum aestivum seedlings

Hexaconazole is one of the triazole complexes that are broadly used as systemic fungicides with non-traditional plant growth regulator properties. Hexaconazole-Cu complex (Hex-Cu) is a new triazole derivative, and the biological effect of Hex-Cu has been rarely studied. In this work, we investigated the functions of Hex-Cu in regulating growth and the response to salt stress in the seedlings of Triticum aestivum. Pretreated with 60μmolL(-1) Hex-Cu, the seedling plants got increased root/shoot ratio by 42.0%, and the contents of chlorophyll and soluble protein were also increased by 38.1% and 27.9%, respectively. Furthermore, Hex-Cu alleviated the growth inhibition caused by salt stress, enabled the seedlings to maintain a higher proline content and lower malondialdehyde accumulation. The functions of Hex-Cu in regulating the expression of proline synthetase (P5CS and P5CR) genes were investigated by quantitative real-time PCR (qPCR). Under 100mmolL(-1) NaCl stress, the expression of P5CS and P5CR in the seedlings by Hex-Cu pretreatment were significantly up-regulated. It attributed to the enhanced salt tolerance in plants.

Role of proline and pyrroline-5-carboxylate metabolism in plant defense against invading pathogens

Pyrroline-5-carboxylate (P5C) is an intermediate product of both proline biosynthesis and catabolism. Recent evidences indicate that proline-P5C metabolism is tightly regulated in plants, especially during pathogen infection and abiotic stress. However, role of P5C and its metabolism in plants has not yet been fully understood. Studies indicate that P5C synthesized in mitochondria has a role in both resistance (R)-gene-mediated and non-host resistance against invading pathogens. Proline dehydrogenase and delta-ornithine amino transferase-encoding genes, both involved in P5C synthesis in mitochondria are implicated in defense response of Nicotiana benthamiana and Arabidopsis thaliana against bacterial pathogens. Such defense response is proposed to involve salicylic acid-dependent pathway, reactive oxygen species (ROS) and hypersensitive response (HR)-associated cell death. Recently HR, a form of programmed cell death (PCD), has been proposed to be induced by changes in mitochondrial P5C synthesis or the increase in P5C levels per se in plants inoculated with either a host pathogen carrying suitable avirulent (Avr) gene or a non-host pathogen. Consistently, A. thaliana mutant plants deficient in P5C catabolism showed HR like cell death when grown in external P5C or proline supplemented medium. Similarly, yeast and plant cells under oxidative stress were shown to increase ROS production and PCD due to increase in P5C levels. Similar mechanism has also been reported as one of the triggers for apoptosis in mammalian cells. This review critically analyzes results from various studies and enumerates the pathways for regulation of P5C levels in the plant cell, especially in mitochondria, during pathogen infection. Further, mechanisms regulating P5C- mediated defense responses, namely HR are outlined. This review also provides new insights into the differential role of proline-P5C metabolism in plants exposed to pathogen infection.