Transcriptional profiling in pearl millet (Pennisetum glaucum L.R. Br.) for identification of differentially expressed drought responsive genes

Omics-driven utilization of wild relatives for empowering pre-breeding in pearl millet

MAIN CONCLUSION

Pearl millet wild relatives harbour novel alleles which could be utilized to broaden genetic base of cultivated species. Genomics-informed pre-breeding is needed to speed up introgression from wild to cultivated gene pool in pearl millet. Rising episodes of intense biotic and abiotic stresses challenge pearl millet production globally. Wild relatives provide a wide spectrum of novel alleles which could address challenges posed by climate change. Pre-breeding holds potential to introgress novel diversity in genetically narrow cultivated Pennisetum glaucum from diverse gene pool. Practical utilization of gene pool diversity remained elusive due to genetic intricacies. Harnessing promising traits from wild pennisetum is limited by lack of information on underlying candidate genes/QTLs. Next-Generation Omics provide vast scope to speed up pre-breeding in pearl millet. Genomic resources generated out of draft genome sequence and improved genome assemblies can be employed to utilize gene bank accessions effectively. The article highlights genetic richness in pearl millet and its utilization with a focus on harnessing next-generation Omics to empower pre-breeding.

Identification of responsive genes to multiple abiotic stresses in rice (Oryza sativa): a meta-analysis of transcriptomics data

Abiotic stresses limit the quantity and quality of rice grain production, which is considered a strategic crop in many countries. In this study, a meta-analysis of different microarray data at seedling stage was performed to investigate the effects of multiple abiotic stresses (drought, salinity, cold situation, high temperature, alkali condition, iron, aluminum, and heavy metal toxicity, nitrogen, phosphorus, and potassium deficiency) on rice. Comparative analysis between multiple abiotic stress groups and their control groups indicated 561 differentially expressed genes (DEGs), among which 422 and 139 genes were up-regulated and down-regulated, respectively. Gene Ontology analysis showed that the process of responding to stresses and stimuli was significantly enriched. In addition, pathways such as metabolic process and biosynthesis of secondary metabolites were identified by KEGG pathway analysis. Weighted correlation network analysis (WGCNA) uncovered 17 distinct co-expression modules. Six modules were significantly associated with genes involved in response to abiotic stresses. Finally, to validate the results of the meta-analysis, five genes, including TIFY9 (JAZ5), RAB16B, ADF3, Os01g0124650, and Os05g0142900 selected for qRT-PCR analysis. Expression patterns of selected genes confirmed the results of the meta-analysis. The outcome of this study could help introduce candidate genes that may be beneficial for use in genetic engineering programs to produce more tolerant crops or as markers for selection.

Azospirillum-Bacillus associations: synergistic effects on in vitro PGP traits and growth of pearl millet at early seedling stage under limited moisture conditions

The association of plant beneficial Azospirillum and Bacillus spp. strains expressing different sets of PGP traits may have complementary or supplementary effects on host plants. In the present investigation, A. formosense and Bacillus spp. strains showing diverse PGP traits (IAA production, nitrogenase activity, phosphate, zinc and potassium solubilization, siderophores, antagonism against phytopathogens, osmotic stress tolerance, etc.) were assessed for compatibility by cross-streaking and co-culturing. Under co-culture (Azospirillum + Bacillus), a significant increase in the expression of PGP traits, nitrogenase activity (up to 89%), phosphate solubilization (upto 236%), siderophore production (upto 20%) was observed as compared to individual Azospirillum culture, indicating synergistic effect of co-culture. IAA production was higher in Azospirillum sp. strains as compared to Bacillus spp. strains, when cultured individually; however, when co-cultured, the IAA levels were in the mid-range indicating the contributory effects of compatible strains. The effect of individual Azospirillum and Bacillus strains and their co-inoculation was also assessed on the growth of pearl millet at early stages under moisture-deficit stress imposed using PEG6000 (0, 10, and 20%). Co-inoculation enhanced seed germination (up to 10, 3, and 6% increase under 0, 10, and 20% PEG, respectively, over individual Azospirillum treatment), root traits (increased root hair density and lateral branches), and seedling vigor indices (up to 22, 32, 43% increase in seed vigor index I and 8, 14, and 10% increase in seed vigor index II under 0, 10, 20% PEG, respectively, over individual Azospirillum treatment) under normal as well as moisture-deficit conditions suggesting the role of Bacillus spp. strains in better adaptation of the plants to stress and higher yield potential. The synergistic effect of co-cultured Azospirillum and Bacillus strains on PGP traits indicated metabolic interplay between the two strains which needs to be further understood. The positive effect of co-inoculation on plant growth under moisture-deficit stress indicated the promise of Azospirillum and Bacillus as a synergistic bioformulation for combating nutrient and drought stress in pearl millet, particularly in nutrient-poor dryland agricultural systems.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03503-4.

Pearl millet response to drought: A review

The C4 grass pearl millet is one of the most drought tolerant cereals and is primarily grown in marginal areas where annual rainfall is low and intermittent. It was domesticated in sub-Saharan Africa, and several studies have found that it uses a combination of morphological and physiological traits to successfully resist drought. This review explores the short term and long-term responses of pearl millet that enables it to either tolerate, avoid, escape, or recover from drought stress. The response to short term drought reveals fine tuning of osmotic adjustment, stomatal conductance, and ROS scavenging ability, along with ABA and ethylene transduction. Equally important are longer term developmental plasticity in tillering, root development, leaf adaptations and flowering time that can both help avoid the worst water stress and recover some of the yield losses via asynchronous tiller production. We examine genes related to drought resistance that were identified through individual transcriptomic studies and through our combined analysis of previous studies. From the combined analysis, we found 94 genes that were differentially expressed in both vegetative and reproductive stages under drought stress. Among them is a tight cluster of genes that are directly related to biotic and abiotic stress, as well as carbon metabolism, and hormonal pathways. We suggest that knowledge of gene expression patterns in tiller buds, inflorescences and rooting tips will be important for understanding the growth responses of pearl millet and the trade-offs at play in the response of this crop to drought. Much remains to be learnt about how pearl millet's unique combination of genetic and physiological mechanisms allow it to achieve such high drought tolerance, and the answers to be found may well be useful for crops other than just pearl millet.

Transcriptome-based analysis of key pathways relating to yield formation stage of foxtail millet under different drought stress conditions

Although foxtail millet, as small Panicoid crop, is of drought resilient, drought stress has a significant effect on panicle of foxtail millet at the yield formation stage. In this study, the changes of panicle morphology, photosynthesis, antioxidant protective enzyme system, reactive oxygen species (ROS) system, and osmotic regulatory substance and RNA-seq of functional leaves under light drought stress (LD), heavy drought stress (HD), light drought control (LDCK) and heavy drought control (HDCK) were studied to get a snap-shot of specific panicle morphological changes, physiological responses and related molecular mechanisms. The results showed that the length and weight of panicle had decreased, but with increased empty abortive rate, and then yield dropped off 14.9% and 36.9%, respectively. The photosynthesis of millet was significantly decreased, like net photosynthesis rate, stomatal conductance and transpiration rate, especially under HD treatment with reluctant recovery from rehydration. Under LD and HD treatment, the peroxidase (POD) was increased by 34% and 14% and the same as H₂O₂ by 34.7% and 17.2% compared with LDCK and HDCK. The ability to produce and inhibit O^2- free radicals under LD treatment was higher than HD. The content of soluble sugar was higher under LD treatment but the proline was higher under HD treatment. Through RNA-seq analysis, there were 2,393 and 3,078 different genes expressed under LD and HD treatment. According to the correlation analysis between weighted gene coexpression network analysis (WGCNA) and physiological traits, the co-expression network of several modules with high correlation was constructed, and some hub genes of millet in response to drought stress were found. The expression changes relating to carbon fixation, sucrose and starch synthesis, lignin synthesis, gibberellin synthesis, and proline synthesis of millet were specifically analyzed. These findings provide a full perspective on how drought affects the yield formation of foxtail millet by constructing one work model thereby providing theoretical foundation for hub genes exploration and drought resistance breeding of foxtail millet.

Genetic insights in pearl millet breeding in the genomic era: challenges and prospects

Pearl millet, a vital staple food and an important cereal, is emerging as crop having various end-uses as feed, food as well as fodder. Advancement in high-throughput sequencing technology has boosted up pearl millet genomic research in past few years. The available draft genome of pearl millet providing an insight into the advancement of several breeding lines. Comparative and functional genomics have untangled several loci and genes regulating adaptive and agronomic traits in pearl millet. Additionally, the knowledge achieved has far away from being applicable in real breeding practices. We believe that the best path ahead is to adopt genome-based approaches for tailored designing of pearl millet as multi-functional crop with outstanding agronomic traits for various end uses. Presently review highlight several novel concepts and techniques in crop breeding, and summarize the recent advances in pearl millet genomic research, peculiarly genome-wide association dissections of several novel alleles and genes for agronomically important traits.

Transcriptome profiling of two rice genotypes under mild field drought stress during grain-filling stage

Drought is one of the most critical abiotic stresses that threaten crop production worldwide. This stress affects the rice crop in all stages of rice development; however, the occurrence during reproductive and grain-filling stages has the most impact on grain yield. Although many global transcriptomic studies have been performed during the reproductive stage in rice, very limited information is available for the grain-filling stage. Hence, we intend to investigate how the rice plant responds to drought stress during the grain-filling stage and how the responses change over time under field conditions. Two rice genotypes were selected for RNA-seq analysis: '4610', previously reported as a moderately tolerant breeding line, and Rondo, an elite indica rice cultivar susceptible to drought conditions. Additionally, 10 agronomic traits were evaluated under normal irrigated and drought conditions. Leaf tissues were collected during grain-filling stages at two time points, 14 and 21 days after the drought treatment, from both the drought field and normal irrigated field conditions. Based on agronomic performances, '4610' was less negatively affected than Rondo under mild drought conditions, and expression profiling largely aligned with the phenotypic data. The transcriptomic data indicated that, in general, '4610' had much earlier responses than its counterpart in mitigating the impact of drought stress. Several key genes and gene families related to drought stress or stress-related conditions were found differentially expressed in this study, including transcription factors, drought tolerance genes and reactive oxygen species scavengers. Furthermore, this study identified novel differentially expressed genes (DEGs) without function annotations that may play roles in drought tolerance-related functions. Some of the important DEGs detected in this study can be targeted for future research.

Research on the drought tolerance mechanism of Pennisetum glaucum (L.) in the root during the seedling stage

BACKGROUND

Drought is one of the major environmental stresses resulting in a huge reduction in crop growth and biomass production. Pearl millet (Pennisetum glaucum L.) has excellent drought tolerance, and it could be used as a model plant to study drought resistance. The root is a very crucial part of plant that plays important roles in plant growth and development, which makes it a focus of research.

RESULTS

In this study, we explored the mechanism of drought tolerance of pearl millet by comparing physiological and transcriptomic data under normal condition and drought treatment at three time points (1 h, 3 h and 7 h) in the root during the seedling stage. The relative electrical conductivity went up from 1 h to 7 h in both control and drought treatment groups while the content of malondialdehyde decreased. A total of 2004, 1538 and 605 differentially expressed genes were found at 1 h, 3 h and 7 h respectively and 12 genes showed up-regulation at all time points. Some of these differentially expressed genes were significantly enriched into 'metabolic processes', 'MAPK signaling pathway' and 'plant hormone signal transduction' such as the ABA signal transduction pathway in GO and KEGG enrichment analysis.

CONCLUSIONS

Pearl millet was found to have a quick drought response, which may occur before 1 h that contributes to its tolerance against drought stress. These results can provide a theoretical basis to enhance the drought resistance in other plant species.

Exogenous abscisic acid and jasmonic acid restrain polyethylene glycol-induced drought by improving the growth and antioxidative enzyme activities in pearl millet

Drought stress is one of the most immense and permanent constraints in agriculture, which leads to a massive loss of crop productivity. However, little is known about the mitigation role of exogenously applied abscisic acid (ABA) and jasmonic acid (JA) in pearl millet (Pennisetum glaucum L.) under PEG-induced drought stress. Therefore, the current study investigated the putative role of exogenous ABA and JA in improving drought stress tolerance in pearl millet. Thirteen-day-old seedlings were exposed to six different treatments as follow; control (ck), PEG-600 (20%), JA (100 μM), ABA (100 μM), PEG+JA, and PEG+ABA, and data were collected at 7 and 14 days after treatment (DAT). Results showed that PEG decreased plant growth while the oxidative damage increased due to over production of H₂ O₂ and MDA content as a result of decreased activities of the antioxidative enzymes including APX, CAT, and SOD in the leaves. However, exogenous ABA and JA positively enhanced the growth profile of seedlings by improving chlorophyll and relative water content under PEG treatment. A significant improvement was observed in the plant defense system resulting from increased activities of antioxidative enzymes due to exogenous ABA and JA under PEG. Overall, the performance of JA was found better than ABA under PEG-induced drought stress, and future investigations are needed to explore the potential effects of these phytohormones on the long-term crop management and productivity under drought stress.

Biotechnological approaches to dissect climate-resilient traits in millets and their application in crop improvement

'Small millets' is a generic term that includes all the millets except pearl millet and sorghum. These small or minor millets constitute eleven species that are marginally cultivated and consumed worldwide. These small millets possess excellent agronomic-, climate-resilient, and nutritional traits, although they lack popularity. Small millets withstand a broad spectrum of environmental stresses and possess better water-use and nitrogen-use efficiencies. Of note, small millets are five- to seven-fold nutritionally rich in terms of protein, bioactive compounds, micro- and macro-nutrients as compared to major cereals. Irrespective of these merits, small millets have received little research attention compared to major millets and cereals. However, the knowledge generated from such studies is significant for the improvement of millets per se and for translating the information to improve major cereals through breeding and transgene-based approaches. Given this, the review enumerates the efforts invested in dissecting the climate-resilient traits in small millets and provides a roadmap for deploying the information in crop improvement of millets as well as cereals in the scenario of climate change.

Morpho-physiological and biochemical changes in finger millet [Eleusine coracana (L.) Gaertn.] under drought stress

Finger millet (Eleusine coracana L. Gaertn.) is a nutritious and climate-resilient crop with a C₄ type carbon fixation pathway. The present study was aimed to assess the drought tolerance capacities of four finger millet genotypes based on their physiological and biochemical characteristics at three different phenological stages. Finger millet genotypes RAU 8, GPU 67, GPU 28 and MS 9272 were subjected to two water regimes, regular irrigation (control) and suspended irrigation (drought stress). During water regimes, morpho-physiological [biomass accumulation, leaf relative water content, and photosynthetic pigments] and biochemical changes [proline content, water soluble carbohydrates, antioxidant enzymes, and malondialdehyde content] were studied during seedling (18th day), vegetative (49th day) and early flowering stages (73rd day). The maintenance of growth especially root growth, biomass accumulation, the differential response in the concentration and changes of pigments, accumulation of proline, water-soluble carbohydrates and increased levels of antioxidant enzymes under drought stress play a major role in differential tolerance in finger millet genotypes that is conferred by the biplot analysis. The genotype RAU 8 is the most drought-tolerant genotype at all the three different phenological stages. Whereas the genotype GPU 67 was identified as sensitive at the seedling stage and its tolerance level was improved at vegetative and early flowering stages. The genotypes GPU 28 and MS 9272 were considered as drought sensitive at all three different phenological stages. Our results provide inputs to the breeders to select genotypes as parents and to design effective strategies in crop improvement programs.

Novel ASR isolated from drought stress responsive SSH library in pearl millet confers multiple abiotic stress tolerance in PgASR3 transgenic Arabidopsis

A genomic resource of drought stress responsive genes/ESTs was generated using Suppression Subtractive Hybridization (SSH) approach in a drought stress tolerant Pennisetum glaucum genotype 841B. Fifty five days old plants were subjected to drought stress after withholding water for different time intervals (10 days, 15 days, 20 days and 25 days). A forward subtractive cDNA library was prepared from isolated RNA of leaf tissue. Differential gene expression under drought stress was validated for selected nine contigs by RT-qPCR. A transcript homologous to Setaria italica ASR3 upregulated under drought stress was isolated from genotype 841B and characterized. Heterologous expression of PgASR3 was validated in Arabidopsis and confirmed under multiple abiotic stress conditions. A total of four independent transgenic lines overexpressing gene PgASR3 were analyzed by Southern blot at T₁ stage. For drought stress tolerance, three independent lines (T₂ stage) were analyzed by biochemical and physiological assays at seedling stage. The growth rate (shoot and root length) of transgenic seedlings improved as compared to WT seedling under differenct abiotic stress conditions. The three transgenic lines were also validated for drought stress tolerance and RT-qPCR analysis, at maturity stage. Under drought stress conditions, the mature transgenic lines showed higher levels of RWC, chlorophyll and proline but lower levels of MDA as compared to WT plants. PgASR3 gene isolated and validated in this study can be utilized for developing abiotic stress tolerant crops.

Transcriptome analysis of heat stress and drought stress in pearl millet based on Pacbio full-length transcriptome sequencing

BACKGROUND

Heat and drought are serious threats for crop growth and development. As the sixth largest cereal crop in the world, pearl millet can not only be used for food and forage but also as a source of bioenergy. Pearl millet is highly tolerant to heat and drought. Given this, it is considered an ideal crop to study plant stress tolerance and can be used to identify heat-resistant genes.

RESULTS

In this study, we used Pacbio sequencing data as a reference sequence to analyze the Illumina data of pearl millet that had been subjected to heat and drought stress for 48 h. By summarizing previous studies, we found 26,299 new genes and 63,090 new transcripts, and the number of gene annotations increased by 20.18%. We identified 2792 transcription factors and 1223 transcriptional regulators. There were 318 TFs and 149 TRs differentially expressed under heat stress, and 315 TFs and 128 TRs were differentially expressed under drought stress. We used RNA sequencing to identify 6920 genes and 6484 genes differentially expressed under heat stress and drought stress, respectively.

CONCLUSIONS

Through Pacbio sequencing, we have identified more new genes and new transcripts. On the other hand, comparing the differentially expressed genes under heat tolerance with the DEGs under drought stress, we found that even in the same pathway, pearl millet responds with a different protein.

Understanding the Genetic Basis of Spike Fertility to Improve Grain Number, Harvest Index, and Grain Yield in Wheat Under High Temperature Stress Environments

Moderate heat stress accompanied by short episodes of extreme heat during the post-anthesis stage is common in most US wheat growing areas and causes substantial yield losses. Sink strength (grain number) is a key yield limiting factor in modern wheat varieties. Increasing spike fertility (SF) and improving the partitioning of assimilates can optimize sink strength which is essential to improve wheat yield potential under a hot and humid environment. A genome-wide association study (GWAS) allows identification of novel quantitative trait loci (QTLs) associated with SF and other partitioning traits that can assist in marker assisted breeding. In this study, GWAS was performed on a soft wheat association mapping panel (SWAMP) comprised of 236 elite lines using 27,466 single nucleotide polymorphisms (SNPs). The panel was phenotyped in two heat stress locations over 3 years. GWAS identified 109 significant marker-trait associations (MTAs) (p ≤ 9.99 x 10-5) related to eight phenotypic traits including SF (a major component of grain number) and spike harvest index (SHI, a major component of grain weight). MTAs detected on chromosomes 1B, 3A, 3B, and 5A were associated with multiple traits and are potentially important targets for selection. More than half of the significant MTAs (60 out of 109) were found in genes encoding different types of proteins related to metabolism, disease, and abiotic stress including heat stress. These MTAs could be potential targets for further validation study and may be used in marker-assisted breeding for improving wheat grain yield under post-anthesis heat stress conditions. This is the first study to identify novel QTLs associated with SF and SHI which represent the major components of grain number and grain weight, respectively, in wheat.

Identification of Differentially Expressed Genes of Rice Under Cadmium Stress Using DDRT-PCR Approach

Cadmium (Cd) is one of the hazardous environmental pollutants, and it can be harmful to human health through consumption of food-plants capable of bioaccumulating Cd. Therefore, lowering cadmium accumulation in plants is highly desirable. Here, a rice cultivar 'Qisanzhan' was studied using differential display reverse transcription-polymerase chain reaction (DDRT-PCR). Fifty-six differentially expressed genes were found in the root tips of 4-leaf stage rice seedlings exposed to 4 and 12 h of 50 µmol/L Cd(NO₃)₂ in a nutrient solution using DDRT-PCR. Further validation using semi-quantitative RT-PCR showed that the expression patterns of 16 genes were consistent with those found in DDRT-PCR. These genes encode receptor-like protein kinase, pleiotropic drug resistance protein, aquaporin protein, plasma membrane ATPase, etc. The differentially genes identified here can be used to obtain a better understanding of the molecular mechanisms of Cd absorption and accumulation in plants.

Milestones achieved in response to drought stress through reverse genetic approaches

Drought stress is the most important abiotic stress that constrains crop production and reduces yield drastically. The germplasm of most of the cultivated crops possesses numerous unknown drought stress tolerant genes. Moreover, there are many reports suggesting that the wild species of most of the modern cultivars have abiotic stress tolerant genes. Due to climate change and population booms, food security has become a global issue. To develop drought tolerant crop varieties knowledge of various genes involved in drought stress is required. Different reverse genetic approaches such as virus-induced gene silencing (VIGS), clustered regularly interspace short palindromic repeat (CRISPR), targeting induced local lesions in genomes (TILLING) and expressed sequence tags (ESTs) have been used extensively to study the functionality of different genes involved in response to drought stress. In this review, we described the contributions of different techniques of functional genomics in the study of drought tolerant genes.

Transcriptomic analysis reveals the differentially expressed genes and pathways involved in drought tolerance in pearl millet [Pennisetum glaucum (L.) R. Br]

Pearl millet is a cereal crop known for its high tolerance to drought, heat and salinity stresses as well as for its nutritional quality. The molecular mechanism of drought tolerance in pearl millet is unknown. Here we attempted to unravel the molecular basis of drought tolerance in two pearl millet inbred lines, ICMB 843 and ICMB 863 using RNA sequencing. Under greenhouse condition, ICMB 843 was found to be more tolerant to drought than ICMB 863. We sequenced the root transcriptome from both lines under control and drought conditions using an Illumina Hi-Seq platform, generating 139.1 million reads. Mapping of sequenced reads against the foxtail millet genome, which has been relatively well-annotated, led to the identification of several differentially expressed genes under drought stress. Total of 6799 and 1253 differentially expressed genes were found in ICMB 843 and ICMB 863, respectively. Pathway and gene function analysis by KEGG online tool revealed that the drought response in pearl millet is mainly regulated by pathways related to photosynthesis, plant hormone signal transduction and mitogen-activated protein kinase signaling. The changes in expression of drought-responsive genes determined by RNA sequencing were confirmed by reverse-transcription PCR for 7 genes. These results are a first step to understanding the molecular mechanisms of drought tolerance in pearl millet and lay a foundation for its genetic improvement.

Transcriptomic signature of drought response in pearl millet (Pennisetum glaucum (L.) and development of web-genomic resources

Pearl millet, (Pennisetum glaucum L.), an efficient (C4) crop of arid/semi-arid regions is known for hardiness. Crop is valuable for bio-fortification combating malnutrition and diabetes, higher caloric value and wider climatic resilience. Limited studies are done in pot-based experiments for drought response at gene-expression level, but field-based experiment mimicking drought by withdrawal of irrigation is still warranted. We report de novo assembly-based transcriptomic signature of drought response induced by irrigation withdrawal in pearl millet. We found 19983 differentially expressed genes, 7595 transcription factors, gene regulatory network having 45 hub genes controlling drought response. We report 34652 putative markers (4192 simple sequence repeats, 12111 SNPs and 6249 InDels). Study reveals role of purine and tryptophan metabolism in ABA accumulation mediating abiotic response in which MAPK acts as major intracellular signal sensing drought. Results were validated by qPCR of 13 randomly selected genes. We report the first web-based genomic resource ( http://webtom.cabgrid.res.in/pmdtdb/ ) which can be used for candidate genes-based SNP discovery programs and trait-based association studies. Looking at climatic change, nutritional and pharmaceutical importance of this crop, present investigation has immense value in understanding drought response in field condition. This is important in germplasm management and improvement in endeavour of pearl millet productivity.

Transcript profiling and gene expression analysis under drought stress in Ziziphus nummularia (Burm.f.) Wright & Arn

Drought is one of the prime abiotic stresses responsible for limiting agricultural productivity. A number of drought responsive genes have been isolated and functionally characterized but these studies have been restricted to a few model plant systems. Very few drought responsive genes have been reported till date from non model drought tolerant plants. The present study aimed at identifying differentially expressed genes from a drought tolerant, non-model plant, Ziziphus nummularia (Burm.f.) Wight & Arn. One month old seedlings of Z. nummularia were subjected to drought stress by 30% Polyethylene glycol (PEG 6000) treatment for 6, 12, 24, 48 and 72 h. A significant reduction in RWC and increase in proline was observed at 24 h and 48 h of treatment. Suppression subtractive hybridization (SSH) library was constructed with drought stressed seedlings after 24 h and 48 h of PEG 6000 treatment. A total of 142 and 530 unigenes from 24 h and 48 h library were identified respectively. Gene ontology studies revealed that about 9.78% and 15.07% unigenes from 24 h and 48 h SSH libraries were expressed in "response to stress". Fifteen putative drought responsive genes identified in SSH library were validated for drought responsive differential expression by RT-qPCR. Significant changes in fold expressions were observed with time in the treated samples compared to the control. A heat map revealing the expression profile of genes was constructed by hierarchical clustering. Various genes identified in SSH libraries can serve as a resource for marker discovery and selection of candidate genes to improve drought tolerance in other susceptible crops.

Systems biology and genome-wide approaches to unveil the molecular players involved in the pre-germinative metabolism: implications on seed technology traits

The pre-germinative metabolism is among the most fascinating aspects of seed biology. The early seed germination phase, or pre-germination, is characterized by rapid water uptake (imbibition), which directs a series of dynamic biochemical events. Among those are enzyme activation, DNA damage and repair, and use of reserve storage compounds, such as lipids, carbohydrates and proteins. Industrial seedling production and intensive agricultural production systems require seed stocks with high rate of synchronized germination and low dormancy. Consequently, seed dormancy, a quantitative trait related to the activation of the pre-germinative metabolism, is probably the most studied seed trait in model species and crops. Single omics, systems biology, QTLs and GWAS mapping approaches have unveiled a list of molecules and regulatory mechanisms acting at transcriptional, post-transcriptional and post-translational levels. Most of the identified candidate genes encode for regulatory proteins targeting ROS, phytohormone and primary metabolisms, corroborating the data obtained from simple molecular biology approaches. Emerging evidences show that epigenetic regulation plays a crucial role in the regulation of these mentioned processes, constituting a still unexploited strategy to modulate seed traits. The present review will provide an up-date of the current knowledge on seed pre-germinative metabolism, gathering the most relevant results from physiological, genetics, and omics studies conducted in model and crop plants. The effects exerted by the biotic and abiotic stresses and priming are also addressed. The possible implications derived from the modulation of pre-germinative metabolism will be discussed from the point of view of seed quality and technology.

Exploration of Genetic and Genomic Resources for Abiotic and Biotic Stress Tolerance in Pearl Millet

Pearl millet is one of the most important small-grained C4 Panicoid crops with a large genome size (∼2352 Mb), short life cycle and outbreeding nature. It is highly resilient to areas with scanty rain and high temperature. Pearl millet is a nutritionally superior staple crop for people inhabiting hot, drought-prone arid and semi-arid regions of South Asia and Africa where it is widely grown and used for food, hay, silage, bird feed, building material, and fuel. Having excellent nutrient composition and exceptional buffering capacity against variable climatic conditions and pathogen attack makes pearl millet a wonderful model crop for stress tolerance studies. Pearl millet germplasm show a large range of genotypic and phenotypic variations including tolerance to abiotic and biotic stresses. Conventional breeding for enhancing abiotic and biotic stress resistance in pearl millet have met with considerable success, however, in last few years various novel approaches including functional genomics and molecular breeding have been attempted in this crop for augmenting yield under adverse environmental conditions, and there is still a lot of scope for further improvement using genomic tools. Discovery and use of various DNA-based markers such as EST-SSRs, DArT, CISP, and SSCP-SNP in pearl millet not only help in determining population structure and genetic diversity but also prove to be important for developing strategies for crop improvement at a faster rate and greater precision. Molecular marker-based genetic linkage maps and identification of genomic regions determining yield under abiotic stresses particularly terminal drought have paved way for marker-assisted selection and breeding of pearl millet cultivars. Reference collections and marker-assisted backcrossing have also been used to improve biotic stress resistance in pearl millet specifically to downy mildew. Whole genome sequencing of pearl millet genome will give new insights for processing of functional genes and assist in crop improvement programs through molecular breeding approaches. This review thus summarizes the exploration of pearl millet genetic and genomic resources for improving abiotic and biotic stress resistance and development of cultivars superior in stress tolerance.

Cereal Crop Proteomics: Systemic Analysis of Crop Drought Stress Responses Towards Marker-Assisted Selection Breeding

Sustainable crop production is the major challenge in the current global climate change scenario. Drought stress is one of the most critical abiotic factors which negatively impact crop productivity. In recent years, knowledge about molecular regulation has been generated to understand drought stress responses. For example, information obtained by transcriptome analysis has enhanced our knowledge and facilitated the identification of candidate genes which can be utilized for plant breeding. On the other hand, it becomes more and more evident that the translational and post-translational machinery plays a major role in stress adaptation, especially for immediate molecular processes during stress adaptation. Therefore, it is essential to measure protein levels and post-translational protein modifications to reveal information about stress inducible signal perception and transduction, translational activity and induced protein levels. This information cannot be revealed by genomic or transcriptomic analysis. Eventually, these processes will provide more direct insight into stress perception then genetic markers and might build a complementary basis for future marker-assisted selection of drought resistance. In this review, we survey the role of proteomic studies to illustrate their applications in crop stress adaptation analysis with respect to productivity. Cereal crops such as wheat, rice, maize, barley, sorghum and pearl millet are discussed in detail. We provide a comprehensive and comparative overview of all detected protein changes involved in drought stress in these crops and have summarized existing knowledge into a proposed scheme of drought response. Based on a recent proteome study of pearl millet under drought stress we compare our findings with wheat proteomes and another recent study which defined genetic marker in pearl millet.

A Transcriptome Meta-Analysis Proposes Novel Biological Roles for the Antifungal Protein AnAFP in Aspergillus niger

Understanding the genetic, molecular and evolutionary basis of cysteine-stabilized antifungal proteins (AFPs) from fungi is important for understanding whether their function is mainly defensive or associated with fungal growth and development. In the current study, a transcriptome meta-analysis of the Aspergillus niger γ-core protein AnAFP was performed to explore co-expressed genes and pathways, based on independent expression profiling microarrays covering 155 distinct cultivation conditions. This analysis uncovered that anafp displays a highly coordinated temporal and spatial transcriptional profile which is concomitant with key nutritional and developmental processes. Its expression profile coincides with early starvation response and parallels with genes involved in nutrient mobilization and autophagy. Using fluorescence- and luciferase reporter strains we demonstrated that the anafp promoter is active in highly vacuolated compartments and foraging hyphal cells during carbon starvation with CreA and FlbA, but not BrlA, as most likely regulators of anafp. A co-expression network analysis supported by luciferase-based reporter assays uncovered that anafp expression is embedded in several cellular processes including allorecognition, osmotic and oxidative stress survival, development, secondary metabolism and autophagy, and predicted StuA and VelC as additional regulators. The transcriptomic resources available for A. niger provide unparalleled resources to investigate the function of proteins. Our work illustrates how transcriptomic meta-analyses can lead to hypotheses regarding protein function and predict a role for AnAFP during slow growth, allorecognition, asexual development and nutrient recycling of A. niger and propose that it interacts with the autophagic machinery to enable these processes.

Drought-Responsive Mechanisms in Plant Leaves Revealed by Proteomics

Plant drought tolerance is a complex trait that requires a global view to understand its underlying mechanism. The proteomic aspects of plant drought response have been extensively investigated in model plants, crops and wood plants. In this review, we summarize recent proteomic studies on drought response in leaves to reveal the common and specialized drought-responsive mechanisms in different plants. Although drought-responsive proteins exhibit various patterns depending on plant species, genotypes and stress intensity, proteomic analyses show that dominant changes occurred in sensing and signal transduction, reactive oxygen species scavenging, osmotic regulation, gene expression, protein synthesis/turnover, cell structure modulation, as well as carbohydrate and energy metabolism. In combination with physiological and molecular results, proteomic studies in leaves have helped to discover some potential proteins and/or metabolic pathways for drought tolerance. These findings provide new clues for understanding the molecular basis of plant drought tolerance.

Setaria viridis as a Model System to Advance Millet Genetics and Genomics

Millet is a common name for a group of polyphyletic, small-seeded cereal crops that include pearl, finger and foxtail millet. Millet species are an important source of calories for many societies, often in developing countries. Compared to major cereal crops such as rice and maize, millets are generally better adapted to dry and hot environments. Despite their food security value, the genetic architecture of agronomically important traits in millets, including both morphological traits and climate resilience remains poorly studied. These complex traits have been challenging to dissect in large part because of the lack of sufficient genetic tools and resources. In this article, we review the phylogenetic relationship among various millet species and discuss the value of a genetic model system for millet research. We propose that a broader adoption of green foxtail (Setaria viridis) as a model system for millets could greatly accelerate the pace of gene discovery in the millets, and summarize available and emerging resources in S. viridis and its domesticated relative S. italica. These resources have value in forward genetics, reverse genetics and high throughput phenotyping. We describe methods and strategies to best utilize these resources to facilitate the genetic dissection of complex traits. We envision that coupling cutting-edge technologies and the use of S. viridis for gene discovery will accelerate genetic research in millets in general. This will enable strategies and provide opportunities to increase productivity, especially in the semi-arid tropics of Asia and Africa where millets are staple food crops.

Improved Salinity Tolerance in Carrizo Citrange Rootstock through Overexpression of Glyoxalase System Genes

Citrus plants are widely cultivated around the world and, however, are one of the most salt stress sensitive crops. To improve salinity tolerance, transgenic Carrizo citrange rootstocks that overexpress glyoxalase I and glyoxalase II genes were obtained and their salt stress tolerance was evaluated. Molecular analysis showed high expression for both glyoxalase genes (BjGlyI and PgGlyII) in 5H03 and 5H04 lines. Under control conditions, transgenic and wild type plants presented normal morphology. In salinity treatments, the transgenic plants showed less yellowing, marginal burn in lower leaves and showed less than 40% of leaf damage compared with wild type plants. The transgenic plants showed a significant increase in the dry weight of shoot but there are no differences in the root and complete plant dry weight. In addition, a higher accumulation of chlorine is observed in the roots in transgenic line 5H03 but in shoot it was lower. Also, the wild type plant accumulated around 20% more chlorine in the shoot compared to roots. These results suggest that heterologous expression of glyoxalase system genes could enhance salt stress tolerance in Carrizo citrange rootstock and could be a good biotechnological approach to improve the abiotic stress tolerance in woody plant species.