Transgenic pearl millet male fertility restorer line (ICMP451) and hybrid (ICMH451) expressing Brassica juncea Nonexpressor of pathogenesis related genes 1 (BjNPR1) exhibit resistance to downy mildew disease

Foliar application of plant-derived peptides decreases the severity of leaf rust (Puccinia triticina) infection in bread wheat (Triticum aestivum L.)

BACKGROUND

Screening and developing novel antifungal agents with minimal environmental impact are needed to maintain and increase crop production, which is constantly threatened by various pathogens. Small peptides with antimicrobial and antifungal activities have been known to play an important role in plant defense both at the pathogen level by suppressing its growth and proliferation as well as at the host level through activation or priming of the plant's immune system for a faster, more robust response against fungi. Rust fungi (Pucciniales) are plant pathogens that can infect key crops and overcome resistance genes introduced in elite wheat cultivars.

RESULTS

We performed an in vitro screening of 18 peptides predominantly of plant origin with antifungal or antimicrobial activity for their ability to inhibit leaf rust (Puccinia triticina, CCDS-96-14-1 isolate) urediniospore germination. Nine peptides demonstrated significant fungicidal properties compared to the control. Foliar application of the top three candidates, β-purothionin, Purothionin-α2 and Defensin-2, decreased the severity of leaf rust infection in wheat (Triticum aestivum L.) seedlings. Additionally, increased pathogen resistance was paralleled by elevated expression of defense-related genes.

CONCLUSIONS

Identified antifungal peptides could potentially be engineered in the wheat genome to provide an alternative source of genetic resistance to leaf rust.

CRISPR for accelerating genetic gains in under-utilized crops of the drylands: Progress and prospects

Technologies and innovations are critical for addressing the future food system needs where genetic resources are an essential component of the change process. Advanced breeding tools like "genome editing" are vital for modernizing crop breeding to provide game-changing solutions to some of the "must needed" traits in agriculture. CRISPR/Cas-based tools have been rapidly repurposed for editing applications based on their improved efficiency, specificity and reduced off-target effects. Additionally, precise gene-editing tools such as base editing, prime editing, and multiplexing provide precision in stacking of multiple traits in an elite variety, and facilitating specific and targeted crop improvement. This has helped in advancing research and delivery of products in a short time span, thereby enhancing the rate of genetic gains. A special focus has been on food security in the drylands through crops including millets, teff, fonio, quinoa, Bambara groundnut, pigeonpea and cassava. While these crops contribute significantly to the agricultural economy and resilience of the dryland, improvement of several traits including increased stress tolerance, nutritional value, and yields are urgently required. Although CRISPR has potential to deliver disruptive innovations, prioritization of traits should consider breeding product profiles and market segments for designing and accelerating delivery of locally adapted and preferred crop varieties for the drylands. In this context, the scope of regulatory environment has been stated, implying the dire impacts of unreasonable scrutiny of genome-edited plants on the evolution and progress of much-needed technological advances.

Characterization and Functional Implications of the Nonexpressor of Pathogenesis-Related Genes 1 (NPR1) in Saccharum

Sugarcane (Saccharum spp.) is an important sugar and energy crop worldwide. As a core regulator of the salicylic acid (SA) signaling pathway, nonexpressor of pathogenesis-related genes 1 (NPR1) plays a significant role in the response of the plant to biotic and abiotic stresses. However, there is currently no report on the NPR1-like gene family in sugarcane. In this study, a total of 18 NPR1-like genes were identified in Saccharum spontaneum and classified into three clades (clade I, II, and III). The cis-elements predicted in the promotors revealed that the sugarcane NPR1-like genes may be involved in various phytohormones and stress responses. RNA sequencing and quantitative real-time PCR analysis demonstrated that NPR1-like genes were differentially expressed in sugarcane tissues and under Sporisorium scitamineum stress. In addition, a novel ShNPR1 gene from Saccharum spp. hybrid ROC22 was isolated by homologous cloning and validated to be a nuclear-localized clade II member. The ShNPR1 gene was constitutively expressed in all the sugarcane tissues, with the highest expression level in the leaf and the lowest in the bud. The expression level of ShNPR1 was decreased by the plant hormones salicylic acid (SA) and abscisic acid (ABA). Additionally, the transient expression showed that the ShNPR1 gene plays a positive role in Nicotiana benthamiana plants’ defense response to Ralstonia solanacearum and Fusarium solani var. coeruleum. This study provided comprehensive information for the NPR1-like family in sugarcane, which should be helpful for functional characterization of sugarcane NPR1-like genes in the future.

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.

Advances in Agrobacterium tumefaciens-mediated genetic transformation of graminaceous crops

Steady increase in global population poses several challenges to plant science research, including demand for increased crop productivity, grain yield, nutritional quality and improved tolerance to different environmental factors. Transgene-based approaches are promising to address these challenges by transferring potential candidate genes to host organisms through different strategies. Agrobacterium-mediated gene transfer is one such strategy which is well known for enabling efficient gene transfer in both monocot and dicots. Due to its versatility, this technique underwent several advancements including development of improved in vitro plant regeneration system, co-cultivation and selection methods, and use of hyper-virulent strains of Agrobacterium tumefaciens harbouring super-binary vectors. The efficiency of this method has also been enhanced by the use of acetosyringone to induce the activity of vir genes, silver nitrate to reduce the Agrobacterium-induced necrosis and cysteine to avoid callus browning during co-cultivation. In the last two decades, extensive efforts have been invested towards achieving efficient Agrobacterium-mediated transformation in cereals. Though high-efficiency transformation systems have been developed for rice and maize, comparatively lesser progress has been reported in other graminaceous crops. In this context, the present review discusses the progress made in Agrobacterium-mediated transformation system in rice, maize, wheat, barley, sorghum, sugarcane, Brachypodium, millets, bioenergy and forage and turf grasses. In addition, it also provides an overview of the genes that have been recently transferred to these graminaceous crops using Agrobacterium, bottlenecks in this technique and future possibilities for crop improvement.

Co-overexpression of Brassica juncea NPR1 (BjNPR1) and Trigonella foenum-graecum defensin (Tfgd) in transgenic peanut provides comprehensive but varied protection against Aspergillus flavus and Cercospora arachidicola

Coexpression of two antifungal genes ( NPR1 and defensin ) in transgenic peanut results in the development of resistance to two major fungal pathogens, Aspergillus flavus and Cercospora arachidicola. Fungal diseases have been one of the principal causes of crop losses with no exception to peanut (Arachis hypogeae L.), a major oilseed crop in Asia and Africa. To address this problem, breeding for fungal disease resistance has been successful to some extent against specific pathogens. However, combating more than one fungal pathogen via breeding is a major limitation in peanut. In the present study, we demonstrated the potential use of co-overexpression of two genes, NPR1 and defensin isolated from Brassica juncea and Trigonella foenum-graecum respectively; that offered resistance towards Aspergillus flavus in peanut. The transgenic plants not only resisted the mycelial growth but also did not accumulate aflatoxin in the seeds. Resistance was also demonstrated against another pathogen, Cercospora arachidicola at varied levels; the transgenic plants showed both reduction in the number of spots and delay in the onset of disease. PCR, Southern and Western blot analysis confirmed stable integration and expression of the transgenes in the transgenic plants. The combinatorial use of the two pathogen resistance genes presents a novel approach to mitigate two important fungal pathogens of peanut.

Global insights into high temperature and drought stress regulated genes by RNA-Seq in economically important oilseed crop Brassica juncea

BACKGROUND

Brassica juncea var. Varuna is an economically important oilseed crop of family Brassicaceae which is vulnerable to abiotic stresses at specific stages in its life cycle. Till date no attempts have been made to elucidate genome-wide changes in its transcriptome against high temperature or drought stress. To gain global insights into genes, transcription factors and kinases regulated by these stresses and to explore information on coding transcripts that are associated with traits of agronomic importance, we utilized a combinatorial approach of next generation sequencing and de-novo assembly to discover B. juncea transcriptome associated with high temperature and drought stresses.

RESULTS

We constructed and sequenced three transcriptome libraries namely Brassica control (BC), Brassica high temperature stress (BHS) and Brassica drought stress (BDS). More than 180 million purity filtered reads were generated which were processed through quality parameters and high quality reads were assembled de-novo using SOAPdenovo assembler. A total of 77750 unique transcripts were identified out of which 69,245 (89%) were annotated with high confidence. We established a subset of 19110 transcripts, which were differentially regulated by either high temperature and/or drought stress. Furthermore, 886 and 2834 transcripts that code for transcription factors and kinases, respectively, were also identified. Many of these were responsive to high temperature, drought or both stresses. Maximum number of up-regulated transcription factors in high temperature and drought stress belonged to heat shock factors (HSFs) and dehydration responsive element-binding (DREB) families, respectively. We also identified 239 metabolic pathways, which were perturbed during high temperature and drought treatments. Analysis of gene ontologies associated with differentially regulated genes forecasted their involvement in diverse biological processes.

CONCLUSIONS

Our study provides first comprehensive discovery of B. juncea transcriptome under high temperature and drought stress conditions. Transcriptome resource generated in this study will enhance our understanding on the molecular mechanisms involved in defining the response of B. juncea against two important abiotic stresses. Furthermore this information would benefit designing of efficient crop improvement strategies for tolerance against conditions of high temperature regimes and water scarcity.

Immuno-affinity purification of PglPGIP1, a polygalacturonase-inhibitor protein from pearl millet: studies on its inhibition of fungal polygalacturonases and role in resistance against the downy mildew pathogen

Polygalacturonase-inhibitor proteins (PGIPs) are important plant defense proteins which modulate the activity of microbial polygalacturonases (PGs) leading to elicitor accumulation. Very few studies have been carried out towards understanding the role of PGIPs in monocot host defense. Hence, present study was taken up to characterize a native PGIP from pearl millet and understand its role in resistance against downy mildew. A native glycosylated PGIP (PglPGIP1) of ~43 kDa and pI 5.9 was immunopurified from pearl millet. Comparative inhibition studies involving PglPGIP1 and its non-glycosylated form (rPglPGIP1; recombinant pearl millet PGIP produced in Escherichia coli) against two PGs, PG-II isoform from Aspergillus niger (AnPGII) and PG-III isoform from Fusarium moniliforme, showed both PGIPs to inhibit only AnPGII. The protein glycosylation was found to impact only the pH and temperature stability of PGIP, with the native form showing relatively higher stability to pH and temperature changes. Temporal accumulation of both PglPGIP1 protein (western blot and ELISA) and transcripts (real time PCR) in resistant and susceptible pearl millet cultivars showed significant Sclerospora graminicola-induced accumulation only in the incompatible interaction. Further, confocal PGIP immunolocalization results showed a very intense immuno-decoration with highest fluorescent intensities observed at the outer epidermal layer and vascular bundles in resistant cultivar only. This is the first native PGIP isolated from millets and the results indicate a role for PglPGIP1 in host defense. This could further be exploited in devising pearl millet cultivars with better pathogen resistance.