Chromosome-level genome assembly of Zizania latifolia provides insights into its seed shattering and phytocassane biosynthesis

Chinese wild rice (Zizania latifolia; family: Gramineae) is a valuable medicinal homologous grain in East and Southeast Asia. Here, using Nanopore sequencing and Hi-C scaffolding, we generated a 547.38 Mb chromosome-level genome assembly comprising 332 contigs and 164 scaffolds (contig N50 = 4.48 Mb; scaffold N50 = 32.79 Mb). The genome harbors 38,852 genes, with 52.89% of the genome comprising repetitive sequences. Phylogenetic analyses revealed close relation of Z. latifolia to Leersia perrieri and Oryza species, with a divergence time of 19.7–31.0 million years. Collinearity and transcriptome analyses revealed candidate genes related to seed shattering, providing basic information on abscission layer formation and degradation in Z. latifolia. Moreover, two genomic blocks in the Z. latifolia genome showed good synteny with the rice phytocassane biosynthetic gene cluster. The updated genome will support future studies on the genetic improvement of Chinese wild rice and comparative analyses between Z. latifolia and other plants.

A stepwise route to domesticate rice by controlling seed shattering and panicle shape

Rice (Oryza sativa L.) is consumed by more than half of the world’s population, but despite its global importance the mechanisms of domestication remain unclear. During domestication, wild rice (O. rufipogon Griff.) was transformed by acquiring non-seed-shattering behaviour, an important genetic change that allowed humans to increase grain yield. However, we show previously identified loci, sh4 and qSH3, are individually insufficient to explain loss of seed shattering nor increases in harvest yield in wild rice. We identify the complementary interaction of key mutations for abscission layer interruption and panicle architecture that were causal in the early domestication of Asian rice. An interruption of abscission layer formation requires both sh4 and qSH3, which presents an apparent barrier to selection of shattering loss. We identified the causal single nucleotide polymorphism at qSH3 within a seed-shattering gene OsSh1 conserved in indica and japonica subspecies, but absent in the circum-aus group of rice. We demonstrate through harvest experiments that seed-shattering alone does not significantly impact yield. Instead, we observed yield increases under a SRR3-controlled closed panicle formation, which is augmented by the integration of sh4 and qSH3 alleles causing a slight inhibition of abscission layer. Complementary manipulation of seed shattering and panicle shape result in a panicle structure that is mechanically stable. We propose a stepwise route in the earliest phase of rice domestication in which selection for visible SRR3-controlled closed panicle morphology was instrumental in the sequential recruitment of sh4 and qSH3 and leading to loss of shattering.Significance StatementRice is one of the most important crops worldwide. Loss of seed shattering in domesticated rice, previously attributed to single mutations such as in sh4, is considered the principal genetic change which resulted in yield increases. However, we show that sh4 is insufficient on its own to cause abscission layer disruption and other genes, such as qSH3 are required, making mechanisms for the initial selection of non-shattering unclear. We show that shattering loss in wild rice genetic backgrounds does not increase yields. We identify an interaction in which a second trait, closed panicle formation controlled by SPR3, both increases yield and facilitates recruitment of sh4 and qSH3 which synergistically augment yield, leading to a stepwise route for rice domestication.

Contribution of Awns to Seed Yield and Seed Shattering in Siberian Wildrye Grown under Irrigated and Rainfed Environments

The seed yield of grass species is greatly dependent on inflorescence morphological traits, starting with spikelets per inflorescence and seeds per spikelet, to kernel size, and then to awns. Previous studies have attempted to estimate the contribution of these traits on the harvested yield of major cereal crops, but little information can be accessed on the influence of awns on seed yield of forage grass species. Siberian wildrye (Elymus sibiricus L.) is a widely important perennial forage grass used to increase forage production in arid and semi-arid grasslands. The grass has long inflorescences with long awns developed at the tip end of the lemmas in the florets. In order to evaluate the effect of awns on Siberian wildrye seed production, awn excision analyses from 10 accessions were performed at flowering stage under irrigated and rainfed regimes. Overall, awn excision reduced thousand-seed weight and seed size under both irrigated and rainfed regimes, which decreased final seed yield per plant. De-awned plants produced significantly more seeds per inflorescence, but spikelets per inflorescence was not influenced by awn excision in either condition. Moreover, histological analyses showed a high degradation of the abscission layer in the awned plants than de-awned ones, and awn excision evidently improved average seed breaking tensile strength (BTS), and thus decreased the degree of seed shattering. In conclusion, the observed significant impact of awn excision on different yield-related traits mirrored the impact of awns on the performance of Siberian wildrye under diverse growing conditions. These results provide useful information for plant breeders, seed producers, and researchers to efficiently improve seed production in Siberian wildrye.

Studies of Vegetative Growth, Inflorescence Development and Eco-Dormancy Formation of Abscission Layers in Streptocarpus formosus (Gesneriaceae)

Streptocarpus formosus (Hilliard & B.L. Burtt) T.J. Edwards is a flowering herbaceous perennial indigenous to South Africa and is part of the rosulate group of herbaceous acaulescent plants within the Gesneriaceae family. According to the National Assessment database for the Red List of South African Plants version 2020.1., the plant is listed as rare. The ornamental use of S. formosus has untapped commercial potential as a flowering indoor pot plant, an outdoor bedding plant for shade and as a cut flower for the vase, all of which are limited by a five-month eco-dormancy period during the late autumn and all through the cold season in the short-day winter months. Viable commercial production will require cultivation techniques that produce flowering plants all year round. This study investigated the effectiveness of applying root zone heating to S. formosus plants grown in deep water culture hydroponics during the eco-dormancy period in preventing abscission layer formation and in encouraging flowering and assessed the growth activity response of the plants. The experiment was conducted over eight weeks during the winter season in the greenhouse at Kirstenbosch Botanical garden in water reservoirs, each maintained at five different experimental temperature treatments (18, 22, 26—control, 30 and 34 °C) applied to 10 sample replicates. The results showed that the lowest hydroponic root zone temperature of 18 °C had the greatest effect on the vegetative growth of S. formosus, with the highest average increases in fresh weight (1078 g), root length (211 cm), overall leaf length (362 cm) and the number of newly leaves formed (177 = n), all noted as statistically significant when compared with the other water temperature treatments, which yielded negative results from reduced vegetative growth. Findings from the study also revealed that while all heated solutions significantly prevented the formation of abscission layers of S. formosus, they had a less significant effect on inflorescence formation, with only 18 °C having the greatest positive effect on flower development.

Variability of Selected Traits in Meadow Fescue (Festuca pratensis Huds.) Plants with Different Susceptibility to Seed Shattering

In meadow fescue (Festuca pratensis Huds.), a perennial fodder grass plant characterized by high quality and yield potential, seed shattering makes seed production difficult. The objective of the research was to compare two subpopulations, differing in a tendency to seed shattering, with respect to their variability in the beginning of the heading and flowering stages, their morphological traits (plant height and panicle length), and changes occurring at the site of the bonding between the caryopsis and the pedicel. The subpopulations were obtained by divergent selection carried out on four meadow fescue cultivars. Significant variability in years and subpopulations in respect of the tested traits was found. The subpopulation with a low tendency to seed shattering was characterized by a 2–3 day delay in the beginning of the heading and flowering stages. However, in both the subpopulations, a good flowering stage synchronization was found, with its variability being several times smaller when compared with the heading stage. Between the starting dates of these stages, a significant correlation was found (r = 0.828; p < 0.01). The clones with a high tendency of seed shattering were approximately 7 cm shorter, while the length of panicles was similar in both the subpopulations. The analysis, which was performed with the use of a scanning microscope, showed that, in genotypes with a low tendency to shattering, the formation of the abscission layer was four days late, which may confirm the effectiveness of the carried out selection.

Pod indehiscence in common bean is associated to the fine regulation of PvMYB26

In legumes, pod shattering occurs when mature pods dehisce along the sutures, and detachment of the valves promotes seed dispersal. In Phaseolus vulgaris (L)., the major locus qPD5.1-Pv for pod indehiscence was identified recently. We developed a BC4/F4 introgression line population and narrowed the major locus down to a 22.5-kb region. Here, gene expression and a parallel histological analysis of dehiscent and indehiscent pods identified an AtMYB26 orthologue as the best candidate for loss of pod shattering, on a genomic region ~11 kb downstream of the highest associated peak. Based on mapping and expression data, we propose early and fine up-regulation of PvMYB26 in dehiscent pods. Detailed histological analysis establishes that pod indehiscence is associated to the lack of a functional abscission layer in the ventral sheath, and that the key anatomical modifications associated with pod shattering in common bean occur early during pod development. We finally propose that loss of pod shattering in legumes resulted from histological convergent evolution and that it is the result of selection at orthologous loci.

Post-harvest Attributes of Muskmelon (Cucumis melo): A Mini Review on the Potential of Value Addition

Cucumis melo is a climacteric melon known for its peculiar musky aroma and sweet taste. It gained its popularity as thirst-quenching and refreshing fruit. Muskmelon is one of the commercially important fruit cultivated throughout the world in temperate, tropical and subtropical regions. The fruit shape may be round to oval, tan or straw coloured with netted peel. The flesh color may be white or orange. Muskmelon with yellow-orange coloured pulp with a network of intertwining green veins at the outside are highly preferred. Maturity stages of muskmelon are classified into 5 types and usually harvested at a maturity stage called ‘full-slip’ condition. The formation of the abscission layer between the vine and fruit determines the maturity of fruit in the field. Maturity of the harvested fruit has greater impact on sugar content, volatile content and the texture. The fruit is abundant in nutritional and medicinal properties. It offers a good source of vitamin A, vitamin C, vitamin B6 and potassium. Muskmelon, being climacteric fruit, cannot be stored for a longer time due to its continuous respiration. Hence, the value addition of muskmelon play a vital role in preserving the fruit in different forms. This review describes the origin, types, maturity indices, nutritional benefits and different value-added products of Cucumis melo.

Pod indehiscence in common bean is associated to the fine regulation of PvMYB26 and a non-functional abscission layer

ABSTRACTIn legumes, pod shattering occurs when mature pods dehisce along the sutures, and detachment of the valves promotes seed dispersal. In Phaseolus vulgaris, the major locus qPD5.1-Pv for pod indehiscence was identified recently. We developed a BC4/F4 introgression line population and narrowed the major locus down to a 22.5-kb region. Here, gene expression and a parallel histological analysis of dehiscent and indehiscent pods identified an AtMYB26 orthologue as the best candidate for loss of pod shattering, on a genomic region ~11 kb downstream of the highest associated peak. Based on mapping and expression data, we propose early and fine up-regulation of PvMYB26 in dehiscent pods. Detailed histological analysis establishes that pod indehiscence is associated to the lack of a functional abscission layer in the ventral sheath, and that the key anatomical modifications associated with pod shattering in common bean occur early during pod development. We finally propose that loss of pod shattering in legumes resulted from histological convergent evolution and that this is the result of selection at orthologous loci.One-sentence summaryA non-functional abscission layer determines the loss of pod shattering; mapping data, and parallel gene expression and histological analysis support PvMYB26 as the candidate gene for pod indehiscence.

Research on the Reasonable Width of the Waterproof Coal Pillar during the Mining of a Shallow Coal Seam Located Close to a Reservoir

Retaining a waterproof coal pillar is the most effective water conservation method for coal seam mining close to a reservoir, and determining a reasonable width for the waterproof coal pillar has been a common problem among mining scholars for a considerably long time. In case of mining a 4−2 coal seam close to the Changjiagou Reservoir in the Zhangjiamao mine, the research methods of theoretical analysis, physical simulation using similar materials, and numerical simulation have been adopted to analyze the overburden strata mining failure features and the surface subsidence law. Additionally, the influences of the width of the coal pillar on the reservoir bank slope stability have been investigated. The results denote that a coal pillar can be divided into a mine-pressure-influenced zone, an effective waterproof zone, and a water-level-influenced zone with respect to water resistance. Furthermore, the width of the waterproof coal pillar was determined to be 107.41 m by theoretical analysis. The simulation test indicated that when the working face advanced close to the reservoir, the reservoir bank exhibited vertical downward as well as transverse abscission layer fractures and the divided topsoil slipped toward the reservoir. Subsequently, the judgment conditions required for determining the critical width of the waterproof coal pillar were proposed based on the requirements to prevent the reservoir bank slope from instability failure and the water gushing accident in goaf. The maximum width of the waterproof coal pillar when the top point on the slope surface experienced reverse horizontal displacement and several key points produced sharp vertical displacements or when the pore pressure in the coal seam roof and floor suddenly became 0 was considered to be the critical width. Furthermore, the critical width was determined to be 96 m via simulation analysis, verifying the rationality of the theoretical method. These results could provide a theoretical basis for determining the width of the waterproof coal pillar of the coal seam located close to a reservoir.