-
1.
Doubled haploid technology for line development in maize: technical advances and prospects.
Chaikam, V, Molenaar, W, Melchinger, AE, Boddupalli, PM
TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik. 2019;(12):3227-3243
-
-
Free full text
-
Abstract
Increased efficiencies achieved in different steps of DH line production offer greater benefits to maize breeding programs. Doubled haploid (DH) technology has become an integral part of many commercial maize breeding programs as DH lines offer several economic, logistic and genetic benefits over conventional inbred lines. Further, new advances in DH technology continue to improve the efficiency of DH line development and fuel its increased adoption in breeding programs worldwide. The established method for maize DH production covered in this review involves in vivo induction of maternal haploids by a male haploid inducer genotype, identification of haploids from diploids at the seed or seedling stage, chromosome doubling of haploid (D0) seedlings and finally, selfing of fertile D0 plants. Development of haploid inducers with high haploid induction rates and adaptation to different target environments have facilitated increased adoption of DH technology in the tropics. New marker systems for haploid identification, such as the red root marker and high oil marker, are being increasingly integrated into new haploid inducers and have the potential to make DH technology accessible in germplasm such as some Flint, landrace, or tropical material, where the standard R1-nj marker is inhibited. Automation holds great promise to further reduce the cost and time in haploid identification. Increasing success rates in chromosome doubling protocols and/or reducing environmental and human toxicity of chromosome doubling protocols, including research on genetic improvement in spontaneous chromosome doubling, have the potential to greatly reduce the production costs per DH line.
-
2.
Maize reproductive development and kernel set under limited plant growth environments.
Borrás, L, Vitantonio-Mazzini, LN
Journal of experimental botany. 2018;(13):3235-3243
Abstract
Maize grain yield is highly related to the number of kernels that are established during the flowering period. Kernel number depends on the accumulation of ear biomass and the efficiency of using this biomass for kernel set. Ear biomass depends on the rate of plant biomass accumulation and the proportion of this biomass that is allocated to the ear. In contrast to other major crops, the proportion of plant biomass that is allocated to the ear is not constant in maize, being almost zero under stress conditions. Fortunately, there is wide native genetic variability for this trait, with major practical implications for crop management and plant breeding. Conditions that inhibit plant growth commonly delay silk appearance relative to male anthesis. Time to silking and silk extrusion, which is a tissue expansion process, is dependent on water turgor and ear biomass accumulation, and the magnitude of this delay is used as a marker to phenotype for stress susceptibility. Ear biomass accumulation can also be used for predicting the number of silks that have been extruded if genotype-specific parameters are known. Here, several mechanistic plant and canopy traits are described, together with their implications for better understanding maize yield determination under limited plant growth environments. An ideal genotype sustains growth in environments with limited water or nutrients, has uniform canopies, has increased biomass partitioning to the ear at reduced plant growth, reaches silking with minimum ear biomass, and has rapid silk extrusion for minimizing developmental delays between competing structures within the ear. All these traits help maximize kernel set and yield at limited plant growth, and most have been indirectly selected by breeders when increasing yield.
-
3.
Maize domestication and gene interaction.
Stitzer, MC, Ross-Ibarra, J
The New phytologist. 2018;(2):395-408
Abstract
Contents Summary 395 I. Introduction 395 II. The genetic basis of maize domestication 396 III. The tempo of maize domestication 401 IV. Genetic interactions and selection during maize domestication 401 V. Gene networks of maize domestication alleles 404 VI. Implications of gene interactions on evolution and selection404 VII. Conclusions 405 Acknowledgements 405 References 405 SUMMARY Domestication is a tractable system for following evolutionary change. Under domestication, wild populations respond to shifting selective pressures, resulting in adaptation to the new ecological niche of cultivation. Owing to the important role of domesticated crops in human nutrition and agriculture, the ancestry and selection pressures transforming a wild plant into a domesticate have been extensively studied. In Zea mays, morphological, genetic and genomic studies have elucidated how a wild plant, the teosinte Z. mays subsp. parviglumis, was transformed into the domesticate Z. mays subsp. mays. Five major morphological differences distinguish these two subspecies, and careful genetic dissection has pinpointed the molecular changes responsible for several of these traits. But maize domestication was a consequence of more than just five genes, and regions throughout the genome contribute. The impacts of these additional regions are contingent on genetic background, both the interactions between alleles of a single gene and among alleles of the multiple genes that modulate phenotypes. Key genetic interactions include dominance relationships, epistatic interactions and pleiotropic constraint, including how these variants are connected in gene networks. Here, we review the role of gene interactions in generating the dramatic phenotypic evolution seen in the transition from teosinte to maize.
-
4.
Developing and deploying climate-resilient maize varieties in the developing world.
Cairns, JE, Prasanna, BM
Current opinion in plant biology. 2018;(Pt B):226-230
Abstract
In sub-Saharan Africa (SSA) and Asia maize yields remain variable due to climate shocks. Over the past decade extensive progress has been made on the development and delivery of climate-resilient maize. In 2016 over 70000 metric tonnes of drought-tolerant maize seed was commercialized in 13 countries in SSA, benefiting an estimated 53 million people. Significant progress is also being made with regard to the development and deployment of elite heat-tolerant maize varieties in South Asia. Increased genetic gain in grain yield under stress-prone environments, coupled with faster replacement of old/obsolete varieties, through intensive engagement with seed companies is essential to protect maize crops grown by smallholders from the changing climates in SSA and Asia.
-
5.
Next-Generation Sequencing Promoted the Release of Reference Genomes and Discovered Genome Evolution in Cereal Crops.
Huang, Y, Liu, H, Xing, Y
Current issues in molecular biology. 2018;:37-50
Abstract
In recent decades, next-generation sequencing (NGS) was developed and brought biology into a new era. Rice, maize, wheat, sorghum and barley are the most important cereal crops and feed most of the world's population. Great progress in the study of cereal genomes has been made with the help of NGS. Reference genome sequence assembly and re-sequencing have grown exponentially. Thus, evolution and comparative genomics are renewed, including origin verification, evolution tracking and so on. In this review, we briefly record the development of sequencing technology, the comparison of next-generation sequencing methods and platforms and summarize the bioinformatics tools used for NGS data analysis. We describe how NGS accelerates reference genome assembly and new evolutionary findings. We finally discuss how to discover more valuable resources and improve cereal breeding in the future.
-
6.
Use of CRISPR/Cas9 for Crop Improvement in Maize and Soybean.
Chilcoat, D, Liu, ZB, Sander, J
Progress in molecular biology and translational science. 2017;:27-46
Abstract
CRISPR/Cas enables precise improvement of commercially relevant crop species by transgenic and nontransgenic methodologies. We have used CRISPR/Cas with or without DNA repair template in both corn and soybean for a range of applications including enhancing drought tolerance, improving seed oil composition, and endowing herbicide tolerance. Importantly, by pairing CRISPR/Cas technology with recent advances in plant tissue culture, these changes can be introduced directly into commercially relevant genotypes. This powerful combination of technologies enables advanced breeding techniques for introducing natural genetic variations directly into product relevant lines with improved speed and quality compared with traditional breeding methods. Variation generated through such CRISPR/Cas enabled advanced breeding approaches can be indistinguishable from naturally occurring variation and therefore should be readily accessible for commercialization. The precision, reach, and flexibility afforded by CRISPR/Cas promise an important role for genome editing in future crop improvement efforts.
-
7.
Maize Lethal Necrosis (MLN), an Emerging Threat to Maize-Based Food Security in Sub-Saharan Africa.
Mahuku, G, Lockhart, BE, Wanjala, B, Jones, MW, Kimunye, JN, Stewart, LR, Cassone, BJ, Sevgan, S, Nyasani, JO, Kusia, E, et al
Phytopathology. 2015;(7):956-65
Abstract
In sub-Saharan Africa, maize is a staple food and key determinant of food security for smallholder farming communities. Pest and disease outbreaks are key constraints to maize productivity. In September 2011, a serious disease outbreak, later diagnosed as maize lethal necrosis (MLN), was reported on maize in Kenya. The disease has since been confirmed in Rwanda and the Democratic Republic of Congo, and similar symptoms have been reported in Tanzania, Uganda, South Sudan, and Ethiopia. In 2012, yield losses of up to 90% resulted in an estimated grain loss of 126,000 metric tons valued at $52 million in Kenya alone. In eastern Africa, MLN was found to result from coinfection of maize with Maize chlorotic mottle virus (MCMV) and Sugarcane mosaic virus (SCMV), although MCMV alone appears to cause significant crop losses. We summarize here the results of collaborative research undertaken to understand the biology and epidemiology of MLN in East Africa and to develop disease management strategies, including identification of MLN-tolerant maize germplasm. We discuss recent progress, identify major issues requiring further research, and discuss the possible next steps for effective management of MLN.
-
8.
Biotechnological advances for combating Aspergillus flavus and aflatoxin contamination in crops.
Bhatnagar-Mathur, P, Sunkara, S, Bhatnagar-Panwar, M, Waliyar, F, Sharma, KK
Plant science : an international journal of experimental plant biology. 2015;:119-32
Abstract
Aflatoxins are toxic, carcinogenic, mutagenic, teratogenic and immunosuppressive byproducts of Aspergillus spp. that contaminate a wide range of crops such as maize, peanut, and cotton. Aflatoxin not only affects crop production but renders the produce unfit for consumption and harmful to human and livestock health, with stringent threshold limits of acceptability. In many crops, breeding for resistance is not a reliable option because of the limited availability of genotypes with durable resistance to Aspergillus. Understanding the fungal/crop/environment interactions involved in aflatoxin contamination is therefore essential in designing measures for its prevention and control. For a sustainable solution to aflatoxin contamination, research must be focused on identifying and improving knowledge of host-plant resistance factors to aflatoxin accumulation. Current advances in genetic transformation, proteomics, RNAi technology, and marker-assisted selection offer great potential in minimizing pre-harvest aflatoxin contamination in cultivated crop species. Moreover, developing effective phenotyping strategies for transgenic as well as precision breeding of resistance genes into commercial varieties is critical. While appropriate storage practices can generally minimize post-harvest aflatoxin contamination in crops, the use of biotechnology to interrupt the probability of pre-harvest infection and contamination has the potential to provide sustainable solution.
-
9.
Biosynthesis, elicitation and roles of monocot terpenoid phytoalexins.
Schmelz, EA, Huffaker, A, Sims, JW, Christensen, SA, Lu, X, Okada, K, Peters, RJ
The Plant journal : for cell and molecular biology. 2014;(4):659-78
-
-
Free full text
-
Abstract
A long-standing goal in plant research is to optimize the protective function of biochemical agents that impede pest and pathogen attack. Nearly 40 years ago, pathogen-inducible diterpenoid production was described in rice, and these compounds were shown to function as antimicrobial phytoalexins. Using rice and maize as examples, we discuss recent advances in the discovery, biosynthesis, elicitation and functional characterization of monocot terpenoid phytoalexins. The recent expansion of known terpenoid phytoalexins now includes not only the labdane-related diterpenoid superfamily but also casbane-type diterpenoids and β-macrocarpene-derived sequiterpenoids. Biochemical approaches have been used to pair pathway precursors and end products with cognate biosynthetic genes. The number of predicted terpenoid phytoalexins is expanding through advances in cereal genome annotation and terpene synthase characterization that likewise enable discoveries outside the Poaceae. At the cellular level, conclusive evidence now exists for multiple plant receptors of fungal-derived chitin elicitors, phosphorylation of membrane-associated signaling complexes, activation of mitogen-activated protein kinase, involvement of phytohormone signals, and the existence of transcription factors that mediate the expression of phytoalexin biosynthetic genes and subsequent accumulation of pathway end products. Elicited production of terpenoid phytoalexins exhibit additional biological functions, including root exudate-mediated allelopathy and insect antifeedant activity. Such findings have encouraged consideration of additional interactions that blur traditionally discrete phytoalexin classifications. The establishment of mutant collections and increasing ease of genetic transformation assists critical examination of further biological roles. Future research directions include examination of terpenoid phytoalexin precursors and end products as potential signals mediating plant physiological processes.
-
10.
Perspective and prospective of pretreatment of corn straw for butanol production.
Baral, NR, Li, J, Jha, AK
Applied biochemistry and biotechnology. 2014;(2):840-53
Abstract
Corn straw, lignocellulosic biomass, is a potential substrate for microbial production of bio-butanol. Bio-butanol is a superior second generation biofuel among its kinds. Present researches are focused on the selection of butanol tolerant clostridium strain(s) to optimize butanol yield in the fermentation broth because of toxicity of bio-butanol to the clostridium strain(s) itself. However, whatever the type of the strain(s) used, pretreatment process always affects not only the total sugar yield before fermentation but also the performance and growth of microbes during fermentation due to the formation of hydroxyl-methyl furfural, furfural and phenolic compounds. In addition, the lignocellulosic biomasses also resist physical and biological attacks. Thus, selection of best pretreatment process and its parameters is crucial. In this context, worldwide research efforts are increased in past 12 years and researchers are tried to identify the best pretreatment method, pretreatment conditions for the actual biomass. In this review, effect of particle size, status of most common pretreatment method and enzymatic hydrolysis particularly for corn straw as a substrate is presented. This paper also highlights crucial parameters necessary to consider during most common pretreatment processes such as hydrothermal, steam explosion, ammonia explosion, sulfuric acid, and sodium hydroxide pretreatment. Moreover, the prospective of pretreatment methods and challenges is discussed.