Transformation of Teosinte (Zea mays ssp. parviglumis) via Biolistic Bombardment of Seedling-Derived Callus Tissues

Modern maize exhibits a significantly different phenotype than its wild progenitor teosinte despite many genetic similarities. Of the many subspecies of Zea mays identified as teosinte, Zea mays ssp. parviglumis is the most closely related to domesticated maize. Understanding teosinte genes and their regulations can provide great insights into the maize domestication process and facilitate breeding for future crop improvement. However, a protocol of genetic transformation, which is essential for gene functional analyses, is not available in teosinte. In this study, we report the establishment of a robust callus induction and regeneration protocol using whorl segments of seedlings germinated from mature seeds of Zea parviglumis. We also report, for the first time, the production of fertile, transgenic teosinte plants using the particle bombardment. Using herbicide resistance genes such as mutant acetolactate synthase (Als) or bialaphos resistance (bar) as selectable markers, we achieved an average transformation frequency of 4.17% (percentage of independent transgenic events in total bombarded explants that produced callus). Expression of visual marker genes of red fluorescent protein tdTomato and β-glucuronidase (gus) could be detected in bombarded callus culture and in T1 and T2 progeny plants. The protocol established in this work provides a major enabling technology for research toward the understanding of this important plant in crop domestication.

N-cycling microbiome recruitment differences between modern and wild Zea mays

Rewilding modern agricultural cultivars by reintroducing beneficial ancestral traits is a proposed approach to improve sustainability of modern agricultural systems. In this study, we compared recruitment of the rhizosphere microbiome among modern inbred maize and wild teosinte to assess whether potentially beneficial plant microbiome traits have been lost through maize domestication and modern breeding. To do this, we surveyed the bacterial and fungal communities along with nitrogen cycling functional groups in the rhizosphere of 6 modern domesticated maize genotypes and ancestral wild teosinte genotypes, while controlling for environmental conditions and starting soil inoculum. Using a combination of high-throughput sequencing and quantitative PCR, we found that the rhizosphere microbiomes of modern inbred and wild teosinte differed substantially in taxonomic composition, species richness, and abundance of N-cycling functional genes. Furthermore, the modern vs wild designation explained 27% of the variation in the prokaryotic microbiome, 62% of the variation in N-cycling gene richness, and 66% of N-cycling gene abundance. Surprisingly, we found that modern inbred genotypes hosted microbial communities with higher taxonomic and functional gene diversity within their microbiomes compared to ancestral genotypes. These results imply that modern maize and wild maize differ in their interaction with N-cycling microorganisms in the rhizosphere and that genetic variation exists within Zea to potentially ‘rewild’ microbiome-associated traits (i.e., exudation, root phenotypes, etc.).

Germoplasma de porumb utilă la crearea liniilor consangvinizate timpurii

The evolution of germplasm incorporated into 477 inbred lines of early maize developed in 1981-2019 years are presented here. It is concluded that for modern maize breeding more useful germplasm are alternative heterotic groups Euroflint mixt, Reid Iodent, BSSS-B37 and Lancaster. A comparative study of 20 inbred lines from 3 heterotic groups demonstrated the performance of Reid Iodent germplasm as seed, female parents. In the mentioned period 35 original inbred lines used as parents of registered hy-brids have been created.

Megabase-scale presence-absence variation with Tripsacum origin was under selection during maize domestication and adaptation

Background Structural variants (SVs) significantly drive genome diversity and environmental adaptation for diverse species. Unlike the prevalent small SVs (< kilobase-scale) in higher eukaryotes, large-size SVs rarely exist in the genome, but they function as one of the key evolutionary forces for speciation and adaptation. Results In this study, we discover and characterize several megabase-scale presence-absence variations (PAVs) in the maize genome. Surprisingly, we identify a 3.2 Mb PAV fragment that shows high integrity and is present as complete presence or absence in the natural diversity panel. This PAV is embedded within the nucleolus organizer region (NOR), where the suppressed recombination is found to maintain the PAV against the evolutionary variation. Interestingly, by analyzing the sequence of this PAV, we not only reveal the domestication trace from teosinte to modern maize, but also the footprints of its origin from Tripsacum, shedding light on a previously unknown contribution from Tripsacum to the speciation of Zea species. The functional consequence of the Tripsacum segment migration is also investigated, and environmental fitness conferred by the PAV may explain the whole segment as a selection target during maize domestication and improvement. Conclusions These findings provide a novel perspective that Tripsacum contributes to Zea speciation, and also instantiate a strategy for evolutionary and functional analysis of the “fossil” structure variations during genome evolution and speciation.

Phosphate Availability Modulates Root Exudate Composition and Rhizosphere Microbial Community in a Teosinte and a Modern Maize Cultivar

Domestication and breeding have impacted interactions between plants and their microbiomes in ways that are only beginning to be understood but may have important implications for recruitment of rhizosphere microorganisms, particularly under stress conditions. We investigated the responses of a modern maize (Zea mays ssp. mays) cultivar and its wild relative, teosinte (Zea mays ssp. parviglumis), to different phosphate availabilities. We appraised responses of the plant-microbial holobiont to phosphate stresses by profiling root exudate metabolomes, and microbial communities in the root endosphere and rhizosphere. We also performed plate assays to quantify phosphate solubilizing microorganisms from the rhizosphere. While root exudate metabolite profiles were distinct between the teosinte and modern maize under high phosphate, both plants shifted exudate compositions in response to phosphate stress toward a common metabolite profile. Root and rhizosphere microbial communities also responded significantly to both plant type and the phosphate availability. A subset of bacterial and fungal taxa were differentially abundant under the different phosphate conditions, with each of the three conditions favoring different taxa. Both teosinte and maize rhizospheres harbored phosphate solubilizing microorganisms under all growth conditions. These results suggest that the root exudation response to phosphate stress was conserved through the domestication of maize from teosinte, shifting exudation levels of specific metabolites. Although microbial communities also shifted, plate-based assays did not detect selective recruitment of phosphate solubilizers in response to phosphate availability.

Gene Expression in Parthenogenic Maize Proembryos

Angiosperm plants reproduce both sexually and asexually (by apomixis). In apomictic plants, the embryo and endosperm develop without fertilization. Modern maize seems to have a broken apomixis-triggering mechanism, which still works in Tripsacum and in Tripsacum–maize hybrids. For the first time, maize lines characterized by pronounced and inheritable high-frequency maternal parthenogenesis were generated 40 years ago, but there are no data on gene expression in parthenogenic maize proembryos. Here we examined for the first time gene expression in parthenogenic proembryos isolated from unpollinated embryo sacs (ESs) of a parthenogenic maize line (AT-4). The DNA-methylation genes (dmt103, dmt105) and the genes coding for the chromatin-modifying enzymes (chr106, hdt104, hon101) were expressed much higher in parthenogenic proembryos than in unpollinated ESs. The expression of the fertilization-independent endosperm (fie1) genes was found for the first time in parthenogenic proembryos and unpollinated ESs. In parthenogenic proembryos, the Zm_fie2 gene was expressed up to two times higher than it was expressed in unpollinated ESs.

Genome editing of maize

Developed over thousands of years largely through human intervention, the modern maize genome can now be precisely modified for agricultural improvement and scientific research. This chapter focuses on progress made in recent decades utilizing site-specific nuclease (SSN) technologies in maize genome engineering. Many SSNs, such as meganucleases, zinc finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated proteins (Cas) have been used in maize for both functional analysis and trait improvement. The chapter summarizes the recent innovations related to maize genome editing using SSN technologies, the type of approaches, target genes and traits, and reagent delivery methods. It also discusses the current challenges as well as potential improvements for maize genome engineering protocols.

A new empirical equation to describe the vertical leaf distribution profile of maize

The characteristic traits of maize (Zea mays L.) leaves affect light interception and photosynthesis. Measurement or estimation of individual leaf area has been described using discontinuous equations or bell-shaped functions. However, new maize hybrids show different canopy architecture, such as leaf angle in modern maize which is more upright and ear leaf and adjacent leaves which are longer than older hybrids. The original equations and their parameters, which have been used for older maize hybrids and grown at low plant densities, will not accurately represent modern hybrids. Therefore, the aim of this paper was to develop a new empirical equation that captures vertical leaf distribution. To characterize the vertical leaf profile, we conducted a field experiment in Jilin province, Northeast China from 2015 to 2018. Our new equation for the vertical distribution of leaf profile describes leaf length, width or leaf area as a function of leaf rank, using parameters for the maximum value for leaf length, width or area, the leaf rank at which the maximum value is obtained, and the width of the curve. It thus involves one parameter less than the previously used equations. By analysing the characteristics of this new equation, we identified four key leaf ranks (4, 8, 14 and 20) for which leaf parameter values need to be quantified in order to have a good estimation of leaf length, width and area. Together, the method of leaf area estimation proposed here adds versatility for use in modern maize hybrids and simplifies the field measurements by using the four key leaf ranks to estimate vertical leaf distribution in maize canopy instead of all leaf ranks.

Characterization of novel regulatory modules controlling leaf angle in maize

Leaf angle is an important agronomic trait determining maize planting density and light penetration into the canopy, and contributes significantly to the yield gain in modern maize hybrids. However, little is known about its molecular mechanism beyond the Liguless1 (LG1) and Liguless2 (LG2) genes. In this study, we found that transcription factor ZmBEH1 is targeted by ZmLG2 and regulates the leaf angle formation by influencing the sclerenchyma cells layers on the adaxial side. ZmBEH1 can interact with transcription factor ZmBZR1, whose expression is directly activated by ZmLG1. Both ZmBEH1 and ZmBZR1 bind to the promoter of ZmSCL28, the third transcription factors that influences the leaf angle. Our study demonstrates novel regulatory modules controlling leaf angle, and provides new gene editing targets for creating optimal maize architecture suitable for dense-planting.