Revisiting Plant Heterosis—From Field Scale to Molecules

Heterosis refers to the increase in biomass, stature, fertility, and other characters that impart superior performance to the F1 progeny over genetically diverged parents. The manifestation of heterosis brought an economic revolution to the agricultural production and seed sector in the last few decades. Initially, the idea was exploited in cross-pollinated plants, but eventually acquired serious attention in self-pollinated crops as well. Regardless of harvesting the benefits of heterosis, a century-long discussion is continued to understand the underlying basis of this phenomenon. The massive increase in knowledge of various fields of science such as genetics, epigenetics, genomics, proteomics, and metabolomics persistently provide new insights to understand the reasons for the expression of hybrid vigor. In this review, we have gathered information ranging from classical genetic studies, field experiments to various high-throughput omics and computational modelling studies in order to understand the underlying basis of heterosis. The modern-day science has worked significantly to pull off our understanding of heterosis yet leaving open questions that requires further research and experimentation. Answering these questions would possibly equip today’s plant breeders with efficient tools and accurate choices to breed crops for a sustainable future.

Genetically diverse mouse models of SARS-CoV-2 infection model clinical variation and cytokine responses in COVID-19

Host genetics are a significant determinant of coronavirus disease 2019 (COVID-19). Animal models that reflect genetic diversity and a range of clinical outcomes observed in human populations are needed to understand mechanisms of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection dynamics and disease. Here, we report a mouse panel comprising the diverse genetic backgrounds of the Collaborative Cross (CC) founder strains crossed to C57BL/6J mice expressing the K18-hACE2 transgene3 that enables infection by SARS-CoV-2. Infection of CCxK18-hACE2 F1 progeny resulted in a spectrum of weight loss, survival, viral replication kinetics, histopathology, and cytokine profiles, some of which were sex-specific. Importantly, survival was closely associated with early type I interferon expression and a phased proinflammatory response distinct from mice with severe disease. Thus, dynamics of inflammatory responses observed in COVID-19 can be modeled in diverse mice that provide a genetically tractable platform for understanding antiviral immunity and evaluating countermeasures.

Neuroprotective role of Curcuma amada in F1 progeny of Juvenile Danio rerio (Zebrafish) from Nickel Chloride Induced Maternal Stress in Gestationally Challenged Adult Fishes

Background: Nickel chloride, a widely occurring heavy metal compound is reported to be neuro toxic to organisms. It was shown to cause detrimental behaviour and biochemical changes. However, its effect on the nervous system of offspring of the victimized organisms and the combating strategies remain unexplained. Such studies could broaden our knowledge on the detrimental effect of toxic compounds and help in developing suitable combating strategies. Purpose: To evaluate the neuroprotective role of ethyl acetate extract (EA) of Curcuma amada in the brain of F1 progeny of Danio rerio (Zebrafish) which has been gestationally exposed to neurotoxicant nickel chloride. Methods: The group distribution of the study was Group I-Control Juvenile Fish, Group II-Juvenile fish obtained from female fishes subjected to nickel chloride exposure for 50 days, Group III-Juvenile fish obtained from female fish subjected to nickel chloride exposure and co- treated with EA extract of Curcuma amada (150µg) from 30th day to 50th day, Group-IV-Juvenile fish treated with EA extract of Curcuma amada (150µg) for 50 days. Neuroprotective role of ethyl acetate extract of Curcuma amada was evaluated in the juvenile fish (F1 progeny) by performing anxiety and memory test, visualizing ultra-structural changes of juvenile brain using transmission electron microscopy and biochemical assay of membrane bound enzymes. Result: In Colour preference test, there was marked reduction in anxiety behavior in the F1 progeny of exposed fish co treated with EA extract of Curcuma amada (Group III) compared to F1 progeny of metal exposed group (Group-II). In the novel object rejection test, there was a marked improvement in the memory and learning pattern of the EA extract of Curcuma amada treated fishes (Group III) compared to F1 progeny of metal exposed group (Group-II). TEM analysis showed clumped and condensed chromatin, peripheral margination and empty mitochondria with loss of cristae and lipid droplets in Nickel exposed model (Group-II) which was found to be alleviated in EA extract of Curcuma amada co-treated group (Group-III). Altered activities of Calcium ATPases and Sodium potassium ATPases was noted in Nickel chloride exposed Group (Group-II) which however were regulated by EA extract of Curcuma amada. Conclusion: The study suggests that Curcuma amada could combat the toxic effect of nickel chloride in the juvenile fish, the progeny of the exposed adult female.

Inheritance of heat tolerance in perennial ryegrass (Lolium perenne, Poaceae): evidence from progeny array analysis

Background Heat stress is considered one of the most important environmental factors influencing plant physiology, growth, development, and reproductive output. The occurrence and damage caused by heat stress will likely increase with global climate change. Thus, there is an urgent need to better understand the genetic basis of heat tolerance, especially in cool season plants. Materials and Methods In this study, we assessed the inheritance of heat tolerance in perennial ryegrass (Lolium perenne L. subspecies perenne) , a cool season grass, through a comparison of two parental cultivars with their offspring. We crossed plants of a heat tolerant cultivar (Kangaroo Valley) with plants of a heat sensitive cultivar (Norlea), to generate 72 F1 hybrid progeny arrays. Both parents and their progeny were then exposed to heat stress for 40 days, and their photosynthetic performance (Fv/Fm values) and leaf H2O2 content were measured. Results As expected, Kangaroo Valley had significantly higher Fv/Fm values and significantly lower H2O2 concentrations than Norlea. For the F1 progeny arrays, values of Fv/Fm decreased gradually with increasing exposure to heat stress, while the content of H2O 2 increased. The progeny had a wide distribution of Fv/Fm and H 2O2 values at 40 days of heat stress. Approximately 95% of the 72 F1 progeny arrays had Fv/Fm values that were equal to or intermediate to the values of the two parental cultivars and 68% of the progeny arrays had H2O2 concentrations equal to or intermediate to their two parents. Conclusion Results of this study indicate considerable additive genetic variation for heat tolerance among the 72 progeny arrays generated from these crosses, and such diversity can be used to improve heat tolerance in perennial ryegrass cultivars. Our findings point to the benefits of combining physiological measurements within a genetic framework to assess the inheritance of heat tolerance, a complex plant response.

Effects of gamma radiation and Bacillus thuringiensis on F1 progeny of Cydia pomonella

Summary The codling moth [Cydia pomonella L. (Lepidoptera: Tortricidae)] is the main pest in most apple orchards in Syria. It causes billions of dollars in loss of fruit crops every year. The present work examined the effects of gamma radiation and Bacillus thuringiensis (BT) on F1 progeny of C. pomonella. The experimental design was based on two factors, namely F1 offspring produced by males irradiated at a dose of 150 Gy, and artificial diet of BT-treated larvae. The first offspring of unirradiated and irradiated C. pomonella males, F1, were from parents treated with a commercial formulation of Bacillus thuringiensis BT (Dipel® 2X). F1 progeny of unirradiated was significantly less susceptible to BT than that of irradiated parents. The results showed high mortality in F1 progeny of C. pomonella when gamma radiation and BT were applied together. The LC50 in F1 progeny was 2.5 ppm for irradiated parents, while it was 13 ppm for unirradiated ones. A significant reduction in the fecundity and egg hatchability of F1 progeny of irradiated parents compared to unirradiated ones was observed. This study demonstrated that for F1 progeny the combination between Inherited Sterility Technique and BT can be useful to achieve an integrated pest management program of codling moth.

Forced Egg Laying Method to Establish F1 Progeny from Field Populations and Laboratory Strains of Anopheles Mosquitoes (Diptera: Culicidae) in Thailand

Successful monitoring of physiological resistance of malaria vectors requires about 150 female mosquitoes for a single set of tests. In some situations, the sampling effort is insufficient due to the low number of field-caught mosquitoes. To address this challenge, we demonstrate the feasibility of using the forced oviposition method for producing F1 from field-caught Anopheles mosquitoes. A total of 430 and 598 gravid Anopheles females from four laboratory strains and five field populations, respectively, were tested. After blood feeding, gravid mosquitoes were individually introduced into transparent plastic vials, containing moistened cotton balls topped with a 4 cm2 piece of filter paper. The number of eggs, hatching larvae, pupation, and adult emergence were recorded daily. The mean number of eggs per female mosquito ranged from 39.3 for Anopheles cracens to 93.6 for Anopheles dirus in the laboratory strains, and from 36.3 for Anopheles harrisoni to 147.6 for Anopheles barbirostris s.l. in the field populations. A relatively high egg hatching rate was found in An. dirus (95.85%), Anopheles minimus (78.22%), and An. cracens (75.59%). Similarly, a relatively high pupation rate was found for almost all test species ranging from 66% for An. minimus to 98.7% for Anopheles maculatus, and lowest for An. harrisoni (43.9%). Highly successful adult emergence rate was observed among 85–100% of pupae that emerged in all tested mosquito populations. The in-tube forced oviposition method is a promising method for the production of sufficient F1 progeny for molecular identification, vector competence, insecticide resistance, and bioassay studies.

Preconceptional smoking alters spermatozoal miRNAs of murine fathers and affects offspring’s body weight

Background Active smoking has been reported among 7% of teenagers worldwide, with ages ranging from 13 to 15 years. An epidemiological study suggested that preconceptional paternal smoking is associated with adolescent obesity in boys. We developed a murine adolescent smoking model before conception to investigate the paternal molecular causes of changes in offspring’s phenotype. Method Male and female C57BL/6J mice were exposed to increasing doses of mainstream cigarette smoke (CS) from onset of puberty for 6 weeks and mated with room air (RA) controls. Results Thirteen miRNAs were upregulated and 32 downregulated in the spermatozoa of CS-exposed fathers, while there were no significant differences in the count and morphological integrity of spermatozoa, as well as the proliferation of spermatogonia between CS- and RA-exposed fathers. Offspring from preconceptional CS-exposed mothers had lower body weights (p = 0.007). Moreover, data from offspring from CS-exposed fathers suggested a potential increase in body weight (p = 0.062). Conclusion We showed that preconceptional paternal CS exposure regulates spermatozoal miRNAs, and possibly influences the body weight of F1 progeny in early life. The regulated miRNAs may modulate transmittable epigenetic changes to offspring, thus influence the development of respiratory- and metabolic-related diseases such as obesity, a mechanism that warrants further studies for elaborate explanations.

Dual Reproductive Cell-Specific Promoter-Mediated Split-Cre/LoxP System Suitable for Exogenous Gene Deletion in Hybrid Progeny of Transgenic Arabidopsis

Genetically modified (GM) crops possess some superior characteristics, such as high yield and insect resistance, but their biosafety has aroused broad public concern. Some genetic engineering technologies have recently been proposed to remove exogenous genes from GM crops. Few approaches have been applied to maintain advantageous traits, but excising exogenous genes in seeds or fruits from these hybrid crops has led to the generation of harvested food without exogenous genes. In a previous study, split-Cre mediated by split intein could recombine its structure and restore recombination activity in hybrid plants. In the current study, the recombination efficiency of split-Cre under the control of ovule-specific or pollen-specific promoters was validated by hybridization of transgenic Arabidopsis containing the improved expression vectors. In these vectors, all exogenous genes were flanked by two loxP sites, including promoters, resistance genes, reporter genes, and split-Cre genes linked to the reporter genes via LP4/2A. A gene deletion system was designed in which NCre was driven by proDD45, and CCre was driven by proACA9 and proDLL. Transgenic lines containing NCre were used as paternal lines to hybridize with transgenic lines containing CCre. Because this hybridization method results in no co-expression of the NCre and CCre genes controlled by reproduction-specific promoters in the F1 progeny, the desirable characteristics could be retained. After self-crossing in F1 progeny, the expression level and protein activity of reporter genes were detected, and confirmed that recombination of split-Cre had occurred and the exogenous genes were partially deleted. The gene deletion efficiency represented by the quantitative measurements of GUS enzyme activity was over 59%, with the highest efficiency of 73% among variable hybrid combinations. Thus, in the present study a novel dual reproductive cell-specific promoter-mediated gene deletion system was developed that has the potential to take advantage of the merits of GM crops while alleviating biosafety concerns.

An Argon-Ion-Induced Pale Green Mutant of Arabidopsis Exhibiting Rapid Disassembly of Mesophyll Chloroplast Grana

Argon-ion beam is an effective mutagen capable of inducing a variety of mutation types. In this study, an argon ion-induced pale green mutant of Arabidopsis thaliana was isolated and characterized. The mutant, designated Ar50-33-pg1, exhibited moderate defects of growth and greening and exhibited rapid chlorosis in photosynthetic tissues. Fluorescence microscopy confirmed that mesophyll chloroplasts underwent substantial shrinkage during the chlorotic process. Genetic and whole-genome resequencing analyses revealed that Ar50-33-pg1 contained a large 940 kb deletion in chromosome V that encompassed more than 100 annotated genes, including 41 protein-coding genes such as TYRAAt1/TyrA1, EGY1, and MBD12. One of the deleted genes, EGY1, for a thylakoid membrane-localized metalloprotease, was the major contributory gene responsible for the pale mutant phenotype. Both an egy1 mutant and F1 progeny of an Ar50-33-pg1 × egy1 cross-exhibited chlorotic phenotypes similar to those of Ar50-33-pg1. Furthermore, ultrastructural analysis of mesophyll cells revealed that Ar50-33-pg1 and egy1 initially developed wild type-like chloroplasts, but these were rapidly disassembled, resulting in thylakoid disorganization and fragmentation, as well as plastoglobule accumulation, as terminal phenotypes. Together, these data support the utility of heavy-ion mutagenesis for plant genetic analysis and highlight the importance of EGY1 in the structural maintenance of grana in mesophyll chloroplasts.