Generating Novel Male Sterile Tomatoes by Editing Respiratory Burst Oxidase Homolog Genes

Hybrid breeding of tomatoes (Solanum lycopersicum), an important vegetable crop, is an effective way to improve yield and enhance disease and stress resistance. However, the efficiency of tomato hybridization is hindered by self-fertilization, which can be overcome using male sterile lines. It has been reported that reactive oxygen species (ROS) act as a key regulator for anther development, mediated by RBOH (Respiratory Burst Oxidase Homolog) genes. Here, two tomato anther-expressed genes, LeRBOH (Solyc01g099620) and LeRBOHE (Solyc07g042460), were selected to cultivate novel tomato male sterile strains. By using a CRISPR/Cas9 system with a two-sgRNA module, the lerboh, lerbohe, and lerboh lerbohe mutant lines were generated, among which the lerbohe and lerboh lerbohe mutants displayed complete male sterility but could accept wild-type pollens and produce fruits normally. Further analysis uncovered significantly decreased ROS levels and abnormal programmed cell death in lerboh lerbohe anthers, indicating a key role of ROS metabolism in tomato pollen development. Taken together, our work demonstrates a successful application of gene editing via CRISPR/Cas9 in generating male sterile tomatoes and afforded helpful information for understanding how RBOH genes regulating tomato reproduction process.

Mitochondrial Proteomics and Transcriptional Analysis of Cytoplasmic Male Sterility in Sugar Beet using iTRAQ and qRT–PCR

Sugar beet (Beta vulgaris L.) is an important raw material for the sugar industry, and its output is second only to sugar cane. Cytoplasmic male sterility (CMS) is a phenomenon of pollen abortion that has important implications in sugar beet hybrid breeding. Male plant sterility is usually considered to be associated with mitochondrial dysfunction. Although mitochondrial genes associated with male sterility have been well explored, the different mitochondrial proteomics of CMS in sugar beet are still poorly understood. In this study, differentially expressed mitochondrial proteomic analysis was performed on the flower buds of the male sterile line (DY5-CMS), its maintainer line (DY5-O) and a fertility restorer line (CL6), using an isobaric tag for relative and absolute quantitation (iTRAQ) technology. A total of 2260 proteins were identified by mass spectrometry, of which 538 were differentially expressed proteins. Most of them were involved in protein metabolism, carbohydrate and energy metabolism, and binding. More specifically, some cysteine and methionine metabolism proteins (A0A0J8BGE0, A0A0J8CZM6, A0A0J8D7W0 and A0A0J8BCR7) may play important roles during the formation of CMS. This study provided an in–depth understanding of the CMS molecular mechanism at the protein level in sugar beet.

TaEXPB5 is responsible for male fertility in thermo-sensitive male-sterility wheat with Aegilops kotschyi cytoplasm

Thermo-sensitive male sterility is of vital importance to heterosis, or hybrid vigor in crop production and hybrid breeding. Therefore, it is meaningful to study the function of the genes related to pollen development and male sterility, which is still not fully understand currently. Here, we conducted comparative analyses to screen fertility related genes using RNA-seq, iTRAQ, and PRM-based assay. A gene encoding expansin protein in wheat, TaEXPB5, was isolated in KTM3315A, which was in the cell wall and preferentially upregulated expression in the fertility anthers. The silencing of TaEXPB5 displayed pollen abortion, the declination or sterility of fertility. Further, cytological investigation indicated that the silencing of TaEXPB5 induced the early degradation of tapetum and abnormal development of pollen wall. These results revealed that the silencing of TaEXPB5 could eliminate the effects of temperature on male fertility, and resulting in functional loss of fertility conversion, which implied that TaEXPB5 may be essential for anther or pollen development and male fertility of KTM3315A. These findings provide a novel insight into molecular mechanism of fertility conversion for thermo-sensitive cytoplasmic male-sterility wheat, and contribute to the molecular breeding of hybrid wheat in the future.

Combining ability and heterosis in plant improvement

Information on combining ability and heterosis of parents and crossings is crucial in breeding efforts. Genetic variety is crucial to the effectiveness of yield improvement efforts because it helps to broaden gene pools in any given crop population. The genotype's ability to pass the intended character to the offspring is referred to as combining ability. As a result, information on combining ability is required to determine the crossing pairs in the production of hybrid varieties. Heterosis is the expression of an F1 hybrid's dominance over its parents in a given feature, as measured not by the trait's absolute value, but by its practical use. To put it another way, heterosis is defined as an increase in the character value of F1 hybrids when compared to the average value of both parents. A plant breeder's ultimate goal is to achieve desirable heterosis (hybrid vigor). In a variety of crop species, heterosis has been widely employed to boost output and extend the adaptability of hybrid types. A crucial requirement for discovering crosses with significant levels of exploitable heterosis is knowledge of the quantity of heterosis in different cross combinations. Any crop improvement program's success is contingent on the presence of a significant level of genetic diversity and heritability. The lack of a broad genetic foundation is the most significant constraint to crop improvement and a major bottleneck in breeding operations. Heterosis is a critical factor in hybrid generation, particularly for traits driven by non-additive gene activity. To get the most out of heterosis for hybrid cultivar production, germplasm must be divided into distinct heterotic groups. Similarly, knowledge on genetic diversity is critical for hybrid breeding and population improvement initiatives because it allows them to analyze genetic diversity, characterize germplasm, and categorize it into different heterotic groupings. In general, general combining ability is used to detect a line's average performance in a hybrid combination, whereas specific combining ability is used to find circumstances where definite combinations perform better or worse than expected based on the mean performance of the lines involved.

Selection Gain of Maize Haploid Inducers for the Tropical Savanna Environments

Lacking elite haploid inducers performing high haploid induction rate (HIR) and agronomic performance is one of fundamental factors hindering the rapid adoption of doubled haploid technology in maize hybrid breeding, especially under tropical savanna climate. Breeding haploid inducers for specific agro-ecology, thus, is indispensable yet challenging. We used temperate inducer Stock6 as genetic source for haploid induction ability and eight tropical maize genotypes as principal donors for agronomic adaptation. Three cycles of modified ear-to-row with 5% intra-family selection were applied in a population set of 78 putative haploid inducer families emphasized on agronomic performance, R1-nj anthocyanin intensity, and inducer seed set. Genetic gains, variance components, and heritability on given traits were estimated. Hierarchical clustering based on five selection criteria was performed to investigate the phenotypic diversity of putative families. Cycle effect was predominant for all observed traits. Realized genetic gain was positive for HIR (0.40% per cycle) and inducer seed set (30.10% or 47.30 seeds per ear per cycle). In this study, we reported the first haploid inducers for regions under tropical savanna climate. Three inducer families, KHI-42, KHI-54, and KHI-64, were promising as they possessed HIR about 7.8% or 14 haploid seeds per tester ear and inducer seed rate about 95.0% or 208 inducer seeds per ear. The breeding method was effective for enhancing the seed set and the expression of R1-nj anthocyanin marker of inducers, yet it showed a low effectiveness to improve haploid induction rate. Introgression of temperate inducer Stock6 into tropical gene pool followed by phenotypic selections through modified ear-to-row selection on inducer seed set and R1-nj marker did not compromise the agronomic traits of tropical inducer families. Implications and further strategies for optimizing genetic gain on HIR are discussed.

Source material from the VIR collection for hybrid breeding of multiple-ear maize

Background. Expanding the genetic polymorphism of maize is an effective way to increase its productivity by involving multiple-ear genotypes in breeding.Materials and methods. In 2007, 596 maize accessions from VIR were assessed at the Kuban Experiment Station of VIR. In 2020, 52 hybrids between multiple-ear and single-ear maize lines were tested in the steppe zone of Kabardino-Balkaria at the site of the OTBOR Agrifirm. Useful agronomic traits were recorded, the coefficient of prolificacy (kmc) was calculated for the source lines and their hybrid progeny from crosses with a single-ear tester, and 52 parent lines were ranked according to the type of inheritance of the prolificacy feature.Results. Accessions that combined prolificacy with other useful agronomic traits were identified. The following accessions were selected for their plant height (score 5, 126–175 cm): k-8819, k-9054, k-15269, k-15355, k-15360, k-15331, k-15877, k-15442, k-15443, k-15445, k-8009, k-14344, k-15195, k-15226 and k-17385. Accessions that excelled in the height of the ear attachment for mechanized harvesting (score 5, 50–70 cm) were as follows: k-8819, k-15269, k-15355, k-15360, k-14394, k-14904, k-14979, k-14968, k-15292, k-15391, k-9289, k-15322, k-15439, k-15442, k-15443 and k-14344. Sources of the following traits were identified: long cob (score 9, > 20 cm): k-9054, k-4535, k-13730, k-14817 and k-14996; higher number of rows per ear (score 5–9, > 16 grain rows): k-14904, k-14979, k-14968, k-15442, k-15330, k-15322 and k-9257; and higher number of grains in a row (score 5–9, > 31 grains per row): k-14904, k-14996, k-15639, k-15353, k-15330, k-15322, k-15344, k-15281, k-15439, k-9357 and k-15237. Ranking 52 accessions according to the test cross results showed that 9 of them produced progeny of the maternal type (no more than one ear), 26 of the intermediate type (1.1–1.5 ears per plant), 11 of the paternal type (1.6–2,0 ears) and 6 of heterotic type (more than 2 ears).

Reduced rice paddy methane emission through dual compound mechanism in novel cultivars

Methane is the second most abundant greenhouse gas after carbon dioxide and its concentrations have risen tenfold in the past decade due to agricultural activity1. Rice paddies are considered a major source of anthropogenic methane, however strategies to mitigate methane emission in rice paddies is not yet successful despite considerable efforts being made. Methane production is caused by microbial communities feeding on organic exudates from the rice root, and regulation of the dominant secretions has been suggested as leading way to put an end to the methane emission from rice paddies. Here, we introduced a new system to reduce methane emission in rice paddies based on the discovery that fumarate and ethanol are two specific rice-orchestrated compounds that determine the levels of methane emission from rice paddies. Moreover, stable low-fumarate high-ethanol secretion lines have been successively bred through hybrid breeding and shown to cut around 70% of methane emission in paddies as compared to control. Approaches to block fumarate reductase or increase ethanol level, were furthermore employed as cultivation managements and resulted in a reduction in methane emissions of around 60%, calculated from two-year four-site field work. All results highlight the application of our findings to largely mitigate influences of rice cultivation on global climate.

Crop Cycle Length Determines Optimal Transplanting Date for Seedlings from Hybrid True Potato Seeds

The technology of hybrid breeding in diploid potatoes creates opportunities to design novel and improved cultivation systems based on hybrid true potato seeds. A promising cultivation pathway to produce seed or ware tubers is by transplanting greenhouse-raised seedlings into the field. This study explored the effects of transplanting date and seedling age on tuber yield, using greenhouse-raised seedlings. Field trials with experimental hybrid genotypes were conducted in three consecutive years. In 2017 and 2018, 4- and 6-week-old seedlings were transplanted at four dates: March, April, May and June. In 2019, transplanting dates included April, May and June and seedling age was 5 weeks. In 2018, the March planting experienced severe frost during the initial field period resulting in crop failure. In 2017 and 2019, plants could withstand shorter and less severe frost events. Seedling age did not significantly affect tuber parameters. Transplanting in June resulted in lower marketable yield (> 28 mm) compared with earlier transplanting dates when crops were harvested in September. At full crop senescence, no differences in marketable yield were observed. The optimal transplanting window, taking into account weather-related risks, is approximately between early April and end May. For some genotypes, crop cycle length was observed to be a more important yield-determining factor than transplanting date.

Water relations composition among Egyptian cotton genotypes under water deficit

Background: water shortage is one of the major factor effects on growth characters and yield of most crops. Objective: this study was conducted to get to know the reactions of some Egyptian cotton genotypes to water deficit. Methods: The genetic materials used in this study included thirteen cotton genotypes belonging to Gossypium barbadense L., from the Cotton Research Institute (CRI), which was devoted to establishing the experimental materials for this investigation. Results: the ratio of GCA/SCA was less than unity for all studied indices, indicating predominance of non-additive gene action (dominance and epistasis), which is an important in exploitation of heterosis through hybrid breeding. Results: The data showed significant reduction in water relationship characters for all parental genotypes under stress conditions. The Egyptian variety Giza 68 gave high values for most water relationship characters. Data revealed that the greater the value of tolerance index is, the larger the yield reduction is under water deficit conditions and the higher the stress sensitivity is becoming. The parental genotypes Giza 96 showed the highest reduction in yield under water deficit conditions. At the same time, the cross combination Minufy x Australy showed higher values of yield reduction followed by the combinations Giza 67 x Australy. Of the male parents, the Russian genotype 10229 recorded the best GCA values for most water relationship characters. At the same time, the female parents, the old Egyptian genotype Giza 67 recorded the best values and exhibited good general combined for most water relationship characters. The cross combinations Giza 86 x Pima S6, Giza 77 x Pima S6, Giza 94 x Dandra and Giza 96 x Australy showed significant desirable SCA effect for most characters. Conclusion: relative water content %, osmotic pressure, chlorophyll and carotenoids content indicates better availability of water in the cell, which increases the photosynthetic rate. Also, the higher level of proline accumulation in the leaves which was recorded under deficit water suggests that the production of proline is probably a common response of plant under water deficit conditions.