Tuning Beforehand: A Foresight on RNA Interference (RNAi) and In Vitro-Derived dsRNAs to Enhance Crop Resilience to Biotic and Abiotic Stresses.

Crop yield is severely affected by biotic and abiotic stresses. Plants adapt to these stresses mainly through gene expression reprogramming at the transcriptional and post-transcriptional levels. Recently, the exogenous application of double-stranded RNAs (dsRNAs) and RNA interference (RNAi) technology has emerged as a sustainable and publicly acceptable alternative to genetic transformation, hence, small RNAs (micro-RNAs and small interfering RNAs) have an important role in combating biotic and abiotic stresses in plants. RNAi limits the transcript level by either suppressing transcription (transcriptional gene silencing) or activating sequence-specific RNA degradation (post-transcriptional gene silencing). Using RNAi tools and their respective targets in abiotic stress responses in many crops is well documented. Many miRNAs families are reported in plant tolerance response or adaptation to drought, salinity, and temperature stresses. In biotic stress, the spray-induced gene silencing (SIGS) provides an intelligent method of using dsRNA as a trigger to silence target genes in pests and pathogens without producing side effects such as those caused by chemical pesticides. In this review, we focus on the potential of SIGS as the most recent application of RNAi in agriculture and point out the trends, challenges, and risks of production technologies. Additionally, we provide insights into the potential applications of exogenous RNAi against biotic stresses. We also review the current status of RNAi/miRNA tools and their respective targets on abiotic stress and the most common responsive miRNA families triggered by stress conditions in different crop species.

Stay-Green Trait: A Prospective Approach for Yield Potential, and Drought and Heat Stress Adaptation in Globally Important Cereals.

The yield losses in cereal crops because of abiotic stress and the expected huge losses from climate change indicate our urgent need for useful traits to achieve food security. The stay-green (SG) is a secondary trait that enables crop plants to maintain their green leaves and photosynthesis capacity for a longer time after anthesis, especially under drought and heat stress conditions. Thus, SG plants have longer grain-filling period and subsequently higher yield than non-SG. SG trait was recognized as a superior characteristic for commercially bred cereal selection to overcome the current yield stagnation in alliance with yield adaptability and stability. Breeding for functional SG has contributed in improving crop yields, particularly when it is combined with other useful traits. Thus, elucidating the molecular and physiological mechanisms associated with SG trait is maybe the key to defeating the stagnation in productivity associated with adaptation to environmental stress. This review discusses the recent advances in SG as a crucial trait for genetic improvement of the five major cereal crops, sorghum, wheat, rice, maize, and barley with particular emphasis on the physiological consequences of SG trait. Finally, we provided perspectives on future directions for SG research that addresses present and future global challenges.

An RNAi-Based Control of Fusarium graminearum Infections Through Spraying of Long dsRNAs Involves a Plant Passage and Is Controlled by the Fungal Silencing Machinery.

Meeting the increasing food and energy demands of a growing population will require the development of ground-breaking strategies that promote sustainable plant production. Host-induced gene silencing has shown great potential for controlling pest and diseases in crop plants. However, while delivery of inhibitory noncoding double-stranded (ds)RNA by transgenic expression is a promising concept, it requires the generation of transgenic crop plants which may cause substantial delay for application strategies depending on the transformability and genetic stability of the crop plant species. Using the agronomically important barley-Fusarium graminearum pathosystem, we alternatively demonstrate that a spray application of a long noncoding dsRNA (791 nt CYP3-dsRNA), which targets the three fungal cytochrome P450 lanosterol C-14α-demethylases, required for biosynthesis of fungal ergosterol, inhibits fungal growth in the directly sprayed (local) as well as the non-sprayed (distal) parts of detached leaves. Unexpectedly, efficient spray-induced control of fungal infections in the distal tissue involved passage of CYP3-dsRNA via the plant vascular system and processing into small interfering (si)RNAs by fungal DICER-LIKE 1 (FgDCL-1) after uptake by the pathogen. We discuss important consequences of this new finding on future RNA-based disease control strategies. Given the ease of design, high specificity, and applicability to diverse pathogens, the use of target-specific dsRNA as an anti-fungal agent offers unprecedented potential as a new plant protection strategy.

Silencing the expression of the salivary sheath protein causes transgenerational feeding suppression in the aphid Sitobion avenae.

Aphids produce gel saliva during feeding which forms a sheath around the stylet as it penetrates through the apoplast. The sheath is required for the sustained ingestion of phloem sap from sieve elements and is thought to form when the structural sheath protein (SHP) is cross-linked by intermolecular disulphide bridges. We investigated the possibility of controlling aphid infestation by host-induced gene silencing (HIGS) targeting shp expression in the grain aphid Sitobion avenae. When aphids were fed on transgenic barley expressing shp double-stranded RNA (shp-dsRNA), they produced significantly lower levels of shp mRNA compared to aphids feeding on wild-type plants, suggesting that the transfer of inhibitory RNA from the plant to the insect was successful. shp expression remained low when aphids were transferred from transgenic plants and fed for 1 or 2 weeks, respectively, on wild-type plants, confirming that silencing had a prolonged impact. Reduced shp expression correlated with a decline in growth, reproduction and survival rates. Remarkably, morphological and physiological aberrations such as winged adults and delayed maturation were maintained over seven aphid generations feeding on wild-type plants. Targeting shp expression therefore appears to cause strong transgenerational effects on feeding, development and survival in S. avenae, suggesting that the HIGS technology has a realistic potential for the control of aphid pests in agriculture.

Effect of Growth Regulators on In Vitro Morphogenic Response of Boscia senegalensis (Pers.) Lam. Poir. Using Mature Zygotic Embryos Explants.

The percent study describes the in vitro responses of mature zygotic embryos of Boscia senegalensis to different concentrations (0.0-5.0 mg/L) of 6-benzyladnine (BA), Thidiazuron (TDZ), α-Naphthalene acetic acid (NAA), and 2, 4-Dichlorophenoxyacetic acid (2, 4-D) supplemented on Murashige and Skoog medium (MS). The plant growth regulators (PGRs) were considerably affected the morphogenetic responses. BA produced adventitious shoots through two ways: direct organogenesis and auxiliary shoot formation. Both 2, 4-D and TDZ tend to produce callus, whereas NAA improve the development of embryos to seedlings. Maximum number of shoots/explant (14.8 ± 0.6) was obtained on MS medium supplemented with 3.0 mg/L BA. 67.0% of excised shoots were rooted either on 1/2 MS medium augmented with or without 0.25 mg/L IBA. The highest number of roots (1.2 ± 0.4) and root length (0.5 ± 0.2 cm) was produced on 0.25 mg/L IBA-containing medium. Regenerated plants were successfully acclimatized and transferred to the green house with 70% survival rate. All the plants appeared morphologically uniform with normal growth pattern. A rapid (30 days), efficient and without subculturing protocol for in vitro regeneration of B. senegalensis was developed.

Establishment of an in vitro micropropagation protocol for Boscia senegalensis (Pers.) Lam. ex Poir.

This report describes in vitro micropropagation of Boscia senegalensis, so-called famine foods, that helped the people in Darfur and Kordofan, Sudan survive during the 1984-1985 famine. Four types of explants prepared from green mature zygotic embryos were cultured on Murashige and Skoog (MS) medium augmented with 1-5 mg/L 6-benzyladenine (BA). The highest number of shoots per explant (14.3±0.9) was achieved on MS medium supplemented with 3 mg/L BA, while the highest shoot length [(3.5±0.4) cm] was obtained with 1 mg/L BA. The shoot cluster, when subcultured to its same medium, significantly increased the rate of shoot multiplication by the end of the third subculture. The maximum mean number of shoots per explant (86.5±3.6) was produced after three multiplication cycles on 3 mg/L BA-supplemented medium. In vitro induced shoots were excised and rooted on half strength MS medium fortified with 0.25 mg/L indole-3-butyric acid (IBA) to obtain complete plantlets. B. senegalensis-regenerated plantlets obtained in vitro for the first time, were hardened and 95% survived under greenhouse conditions.