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Title: Ovary abortion is prevalent in diverse maize inbred lines and is under genetic control
Abstract
Crop improvement programs focus on characteristics that are important for plant productivity. Typically genes underlying these traits are identified and stacked to create improved cultivars. Hence, identification of valuable traits for plant productivity is critical for plant improvement. Here we describe an important characteristic for maize productivity. Despite the fact mature maize ears are typically covered with kernels, we find that only a fraction of ovaries give rise to mature kernels. Non-developed ovaries degenerate while neighboring fertilized ovaries produce kernels that fill the ear. Abortion occurs throughout the ear, not just at the tip. We show that the fraction of aborted ovaries/kernels is genetically controlled and varies widely among maize lines, and low abortion genotypes are rare. Reducing or eliminating ovary abortion could substantially increase yield, making this characteristic a new target for selection in maize improvement programs.
Maize (Zea Mays) is one of the world’s most important crops. Hybrid maize lines resulted a major improvement in corn production in the previous and current centuries. Understanding the genetic mechanisms of the corn production associated traits greatly facilitate the development of superior hybrid varieties.
Result
In this study, four ear traits associated with corn production of Nested Association Mapping (NAM) population were analyzed using a full genetic model, and further, optimal genotype combinations and total genetic effects of current best lines, superior lines, and superior hybrids were predicted for each of the traits at four different locations. The analysis identified 21–34 highly significant SNPs (−log10P > 5), with an estimated total heritability of 37.31–62.34%, while large contributions to variations was due to dominance, dominance-related epistasis, and environmental interaction effects ($${h}_{D+}^2\hat{=}$$14.06% ~ 49.28%), indicating these factors contributed significantly to phenotypic variations of the ear traits. Environment-specific genetic effects were also discovered to be crucial for maize ear traits. There were four SNPs found for three ear traits: two for ear length and weight, and two for ear row number and length. Using the Enumeration method and the stepwise tuning technique, optimum multi-locus genotype combinations for superior lines were identified based on the information obtained from GWAS.
Conclusions
Predictions of genetic breeding values showed that different genotype combinations in different geographical regions may be better, and hybrid-line variety breeding with homozygote and heterozygote genotype combinations may have a greater potential to improve ear traits.
The developmental genetics of reproductive structure control in maize must consider both the staminate florets of the tassel and the pistillate florets of the ear synflorescences. Pistil abortion takes place in the tassel florets, and stamen arrest is affected in ear florets to give rise to the monoecious nature of maize. Gibberellin (GA) deficiency results in increased tillering, a dwarfed plant syndrome, and the retention of anthers in the ear florets of maize. Thesilkless1mutant results in suppression of silks in the ear. We demonstrate in this study that jasmonic acid (JA) and GA act independently and show additive phenotypes resulting in androeciousdwarf1;silkless1double mutant plants. The persistence of pistils in the tassel can be induced by multiple mechanisms, including JA deficiency, GA excess, genetic control of floral determinacy, and organ identity. Thesilkless1mutant can suppress both silks in the ear and the silks in the tassel of JA‐deficient and AP2 transcription factortasselseedmutants. We previously demonstrated that GA production was required for brassinosteroid (BR) deficiency to affect persistence of pistils in the tassel. We find that BR deficiency affects pistil persistence by an independent mechanism from thesilkless1mutant and JA pathway. Thesilkless1mutant did not prevent the formation of pistils in the tassel bynana plant2in double mutants. In addition, we demonstrate that there is more to thesilkless1mutant than just a suppression of pistil growth. We document novel phenotypes ofsilkless1mutants including weakly penetrant ear fasciation and anther persistence in the ear florets. Thus, the JA/AP2 mechanism of pistil retention in the tassel and silk growth in the ear are similarly sensitive to loss of the SILKLESS1 protein, while the BR/GA mechanism is not.
Structural variation in plant genomes is a significant driver of phenotypic variability in traits important for the domestication and productivity of crop species. Among these are traits that depend on functional meristems, populations of stem cells maintained by the CLAVATA-WUSCHEL (CLV-WUS) negative feedback-loop that controls the expression of the WUS homeobox transcription factor. WUS function and impact on maize development and yield remain largely unexplored. Here we show that the maize dominantBarren inflorescence3(Bif3) mutant harbors a tandem duplicated copy of theZmWUS1gene,ZmWUS1-B, whose novel promoter enhances transcription in a ring-like pattern. Overexpression ofZmWUS1-Bis due to multimerized binding sites for type-B RESPONSE REGULATORs (RRs), key transcription factors in cytokinin signaling. Hypersensitivity to cytokinin causes stem cell overproliferation and major rearrangements ofBif3inflorescence meristems, leading to the formation of ball-shaped ears and severely affecting productivity. These findings establishZmWUS1as an essential meristem size regulator in maize and highlight the striking effect of cis-regulatory variation on a key developmental program.
Herr, Andrew W.; Adak, Alper; Carroll, Matthew E.; Elango, Dinakaran; Kar, Soumyashree; Li, Changying; Jones, Sarah E.; Carter, Arron H.; Murray, Seth C.; Paterson, Andrew; et al(
, Crop Science)
Abstract
High‐throughput phenotyping (HTP) with unoccupied aerial systems (UAS), consisting of unoccupied aerial vehicles (UAV; or drones) and sensor(s), is an increasingly promising tool for plant breeders and researchers. Enthusiasm and opportunities from this technology for plant breeding are similar to the emergence of genomic tools ∼30 years ago, and genomic selection more recently. Unlike genomic tools, HTP provides a variety of strategies in implementation and utilization that generate big data on the dynamic nature of plant growth formed by temporal interactions between growth and environment. This review lays out strategies deployed across four major staple crop species: cotton (Gossypium hirsutumL.), maize (Zea maysL.), soybean (Glycine maxL.), and wheat (Triticum aestivumL.). Each crop highlighted in this review demonstrates how UAS‐collected data are employed to automate and improve estimation or prediction of objective phenotypic traits. Each crop section includes four major topics: (a) phenotyping of routine traits, (b) phenotyping of previously infeasible traits, (c) sample cases of UAS application in breeding, and (d) implementation of phenotypic and phenomic prediction and selection. While phenotyping of routine agronomic and productivity traits brings advantages in time and resource optimization, the most potentially beneficial application of UAS data is in collecting traits that were previously difficult or impossible to quantify, improving selection efficiency of important phenotypes. In brief, UAS sensor technology can be used for measuring abiotic stress, biotic stress, crop growth and development, as well as productivity. These applications and the potential implementation of machine learning strategies allow for improved prediction, selection, and efficiency within breeding programs, making UAS HTP a potentially indispensable asset.
Maize ear size and kernel number differ among lines, however, little is known about the molecular basis of ear length and its impact on kernel number. Here, we characterize a quantitative trait locus,qEL7, to identify a maize gene controlling ear length, flower number and fertility.qEL7encodes 1-aminocyclopropane-1- carboxylate oxidase2 (ACO2), a gene that functions in the final step of ethylene biosynthesis and is expressed in specific domains in developing inflorescences. Confirmation ofqEL7by gene editing ofZmACO2leads to a reduction in ethylene production in developing ears, and promotes meristem and flower development, resulting in a ~13.4% increase in grain yield per ear in hybrids lines. Our findings suggest that ethylene serves as a key signal in inflorescence development, affecting spikelet number, floral fertility, ear length and kernel number, and also provide a tool to improve grain productivity by optimizing ethylene levels in maize or in other cereals.
Gustin, Jeffery L., Boehlein, Susan K., Shaw, Janine R., Junior, Weschester, Settles, A. Mark, Webster, Ashley, Tracy, William F., and Hannah, L. Curtis. Ovary abortion is prevalent in diverse maize inbred lines and is under genetic control. Scientific Reports 8.1 Web. doi:10.1038/s41598-018-31216-9.
Gustin, Jeffery L., Boehlein, Susan K., Shaw, Janine R., Junior, Weschester, Settles, A. Mark, Webster, Ashley, Tracy, William F., & Hannah, L. Curtis. Ovary abortion is prevalent in diverse maize inbred lines and is under genetic control. Scientific Reports, 8 (1). https://doi.org/10.1038/s41598-018-31216-9
Gustin, Jeffery L., Boehlein, Susan K., Shaw, Janine R., Junior, Weschester, Settles, A. Mark, Webster, Ashley, Tracy, William F., and Hannah, L. Curtis.
"Ovary abortion is prevalent in diverse maize inbred lines and is under genetic control". Scientific Reports 8 (1). Country unknown/Code not available: Nature Publishing Group. https://doi.org/10.1038/s41598-018-31216-9.https://par.nsf.gov/biblio/10153697.
@article{osti_10153697,
place = {Country unknown/Code not available},
title = {Ovary abortion is prevalent in diverse maize inbred lines and is under genetic control},
url = {https://par.nsf.gov/biblio/10153697},
DOI = {10.1038/s41598-018-31216-9},
abstractNote = {Abstract Crop improvement programs focus on characteristics that are important for plant productivity. Typically genes underlying these traits are identified and stacked to create improved cultivars. Hence, identification of valuable traits for plant productivity is critical for plant improvement. Here we describe an important characteristic for maize productivity. Despite the fact mature maize ears are typically covered with kernels, we find that only a fraction of ovaries give rise to mature kernels. Non-developed ovaries degenerate while neighboring fertilized ovaries produce kernels that fill the ear. Abortion occurs throughout the ear, not just at the tip. We show that the fraction of aborted ovaries/kernels is genetically controlled and varies widely among maize lines, and low abortion genotypes are rare. Reducing or eliminating ovary abortion could substantially increase yield, making this characteristic a new target for selection in maize improvement programs.},
journal = {Scientific Reports},
volume = {8},
number = {1},
publisher = {Nature Publishing Group},
author = {Gustin, Jeffery L. and Boehlein, Susan K. and Shaw, Janine R. and Junior, Weschester and Settles, A. Mark and Webster, Ashley and Tracy, William F. and Hannah, L. Curtis},
}
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