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ARS Home » Midwest Area » Ames, Iowa » Corn Insects and Crop Genetics Research » Research » Research Project #434359

Research Project: Genetic Optimization of Maize for Different Production Environments

Location: Corn Insects and Crop Genetics Research

2021 Annual Report


Objectives
Objective 1: Develop improved maize phenotyping methods based on process-based crop growth models and high throughput phenotyping methods. Subobjective 1.1: Develop and validate crop growth model calibrations for diverse maize hybrids to predict maize hybrid performance across diverse environments. Subobjective 1.2: Evaluate high throughput biochemical and metabolic assays for calibration of crop growth models and prediction of maize grain yield. Subobjective 1.3: Evaluate remote sensing approaches for improving prediction of maize performance and crop growth model calibration. Objective 2: Understand the molecular genetic control of gametophytic incompatibility. Subobjective 2.1: Determine if ZmPme3 complements the ga1 allele to restore the female function of Ga1-s. Subobjective 2.2: Determine the biochemical mechanism of pollen exclusion by the Ga1 system using E. coli expressed ZmPME3. Subobjective 2.3: Identify binding partners of ZmPME3.


Approach
In order to used hybrid-specific crop growth models to understand factors contributing to genotype by environment interactions, replicated field trials of hybrid corn varieties will be carried out and evaluated for morphological, phonological and chemical traits. Together with environmental data, these data will be used to develop crop growth models with publicly available software. Valuable measures of agronomic performance such as grain yield of the specific hybrids in the study will be predicted. These models will be validated using actual measurements of agronomic performance and used to predict performance in additional environmental conditions. In order to understand to molecular genetic control mechanism of gametophytic incompatibility, we will construct a transgene encoding ZmPME3 and use it to complement the ga1 phenotype. A second transgene will be used to mutationally inactivate ZmPME3. All transgenic lines will be evaluated for their ability to exclude unwanted pollen in replicated field trials. In addition, ZmPME will be produced in a bacterial expression system and purified. The activity of the purified protein will be characterized using pectin methylesterase activity assays and the effect of this protein on pollen tube growth will be evaluated in vitro.


Progress Report
Objective 1: Calibration and validation of crop growth models has been completed. Complete calibrations and sensitivity analyses for 12 maize hybrids indicated which growth model parameters are most important for differentiating hybrids. Simulations of maize hybrid performance for the 12 hybrids across six years and nine locations to validate the ability of models to predict performance across a wide range of environmental conditions. Validation work indicated that correlation of simulated hybrid performance was variable among years and among hybrids, i.e., some years and some hybrids had low correlations between simulated and observed yield. Current work is focused on sensitivity analyses to determine which crop and environmental parameters most influence genotype by environment interaction and how to incorporate soluble carbohydrate analysis and aerial image analysis to improve calibrations. Objective 2. Biochemical characterization of genes that control cross compatibility in maize. In order to understand the biochemical mechanisms that control pollination, we plan to move the relevant genes into another organism to make it easier to study them. Because expression of these genes was not successful in E. coli, we undertook the contingency plan of expressing these genes in the yeast Picia pastoris. New constructs were generated to do this. In addition to expressing the original gene we identified that controls pollination, we are also expressing two others because new information indicates that these genes are involved in controlling cross compatibility as well. Understanding how these genes function will allow researchers to develop maize varieties with greater genetic purity. Related to this work, we completed data collection on an experiment comparing the ability of field corn and popcorn to exclude pollen when carrying the Ga1-s allele. Ga1-S can be used in production systems to exclude unwanted pollen, for example, it can keep GMO pollen from contaminating organic corn fields, or field corn from contaminating popcorn. Preliminary analysis indicates that field corn can exclude pollen as well as popcorn, however variation in field corn necessitates testing of each hybrid to ensure that pollen exclusion is effective . This result may impact regulation of field corn carrying the Ga1-s allele for organic and GMO-free corn production systems. Popcorn carrying Ga1-S is currently subject to less stringent regulations than field corn carrying Ga1-s. Our results suggest that field corn varieties shown to have effective pollen exclusion systems could be safely produced under the regulatory system currently in place for popcorn without increased risk of unwanted pollen contamination. This would reduce the regulatory burden on organic or GMO-free field corn producers. A manuscript with these results is in preparation. In grant funded research, with researchers from Iowa State University, University of Illinois and University of Puerto Rico, we selected germplasm and made initial crosses required for testing a new rapid cycling breeding program that will allow improved varieties to be developed in less time. This research involves combining new technologies (doubled haploid technology and genomic selection) to develop corn varieties well suited to organic seed production systems. This research will give organic corn producers more corn varieties to choose from. We initiated a new project based on our project plan research into the Ga1 locus of maize. We took an approach that is similar to the one used to study the Ga1 locus and studied the Ga2 locus, which like Ga1, controls cross compatibility. Having two such systems available will allow plant breeders to improve genetic purity of more market classes of maize. We identified a candidate gene for this locus, which appears to function very much like Ga1. In cooperation with researchers from the Carnegie Institute and UC Davis we are carrying out additional experiments to confirm these results prior to publication.


Accomplishments
1. Development of a biochemical model for cross-incompatibility systems in maize. Cross-incompatibility systems in maize determine what plants can successfully cross-pollinate each other. These systems have great potential for controlling genetic purity, including reducing genetically modified organism (GMO) contamination in organic corn. While these systems have been studied genetically for more than 100 years, researchers have only recently learned the molecular identity of the genes involved, and how they work is still a mystery. Working with researchers from the Indiana Crop Improvement Association and the Carnegie Institute, ARS researchers in Ames, Iowa, proposed a biochemical model for how the genes work to prevent pollination, based on the predicted functions of the newly-identified genes that control the processes. This model provides researchers with hypotheses to test, for example that the level of pectinmethyesterase activity determines whether pollinations are successful, and that a specific interaction between a pectinmethylesterase and a pectinmethyesterase inhibitor is needed to determine the level of pectinmethyesterase activity. Testing these hypotheses will lead to a better understanding of how cross incompatibility systems work. It also provides a framework for engineering novel cross incompatibility systems with improved functionality. Understanding cross incompatibility systems at the biochemical level will allow plant breeders to develop new varieties of maize with increased genetic purity.


Review Publications
Khamphasan, P., Lomthaisong, K., Harakotr, B., Scott, M.P., Lertrat, K., Suriharn, B. 2020. Combining ability and heterosis for agronomic traits, husk and cob pigment concentration of maize. Agriculture. 10(11). Article 510. https://doi.org/10.3390/agriculture10110510.
Sukto, S., Lomthaisong, K., Sanitchon, J., Chankaew, S., Scott, M.P., Lubberstedt, T.P., Lertrat, K., Suriham, B. 2020. Variability in prolificacy, total carotenoids, lutein, and zeaxanthin of yellow small-ear waxy corn germplasm. International Journal of Agronomy. 2020. Article 8818768. https://doi.org/10.1155/2020/8818768.
Lu, Y., Moran Lauter, A., Makkena, S., Scott, M.P., Evans, M.M. 2020. Insights into the molecular control of cross-incompatibility in Zea mays. Plant Reproduction. 33: 117-128. https://doi.org/10.1007/s00497-020-00394-w.