Uncovering hidden genetic variation in photosynthesis of field‐grown maize under ozone pollution

Ozone is the most damaging air pollutant to crops, currently reducing Midwest US maize production by up to 10%, yet there has been very little effort to adapt germ‐ plasm for ozone tolerance. Ozone enters plants through stomata, reacts to form reactive oxygen species in the apoplast and ultimately decreases photosynthetic C gain. In this study, 10 diverse inbred parents were crossed in a half‐diallel design to create 45 F1 hybrids, which were tested for ozone response in the field using free air concentration enrichment (FACE). Ozone stress increased the heritability of pho‐ tosynthetic traits and altered genetic correlations among traits. Hybrids from par‐ ents Hp301 and NC338 showed greater sensitivity to ozone stress, and disrupted relationships among photosynthetic traits. The physiological responses underlying sensitivity to ozone differed in hybrids from the two parents, suggesting multiple mechanisms of response to oxidative stress. FACE technology was essential to this evaluation because genetic variation in photosynthesis under elevated ozone was not predictable based on performance at ambient ozone. These findings suggest that selection under elevated ozone is needed to identify deleterious alleles in the world's largest commodity crop

Utilizing maize genomics for pre-breeding insights

Tropospheric ozone (O3) is estimated to cause billions of dollars in global crop losses, but few studies have investigated the effects of elevated O3 on growth and development of C4 crop plants. Free Air Concentration Enrichment (FACE) field experiments were used to evaluate the response of diverse maize inbred and hybrid lines under elevated O3 concentrations ([O3]). Lines were scored for flowering phenology and ear architecture traits. A multi-year analysis showed inconsistent effects of O3 on development. Hybrid ear length and diameter and inbred ear length were all significantly reduced under elevated [O3] compared to ambient conditions. Knowledge about the identity and location of agriculturally important quantitative trait loci (QTL) provides the basis for marker assisted selection in breeding programs. B73 and Mo17 Nearly Isogenic Lines (NILs) were evaluated at the FACE facility for leaf damage and QTL were mapped. In Mo17 NILs, a significant leaf damage QTL was identified on chromosome 2 at ~161 Mb (AGPv3). Results show that B73 introgressions into Mo17 in this region made NILs more susceptible. Leaf damage scores from the field in 2016 and 2017 had a strongly significant correlation (r = 0.93). Field and growth chamber results best fit is non-linear. It appears chambers can identify damage versus no-damage, but not a continuous degree of damage as seen in the field. This indicates the potential for higher-throughput phenotyping and fine mapping of early season O3 damage QTL in a controlled environment. Sensitive and tolerant NILs were identified. Co-dominant insertion/deletion markers flanking the QTL interval were designed and validated in parents and hybrids. This research supplies the resources for future experiments that combine growth chamber phenotyping and genetic fine-mapping to determine the gene(s) underlying this QTL for O3 tolerance. Current doubled haploid (DH) inducer markers are inefficient and have a higher probability of misclassification when used for classification of tropical germplasm. Yg3-N1582, a rare dominant mutant obtained from ethyl methanesulfonate (EMS) mutagenesis, has not been previously mapped. Phenotypically, Yg3-N1582 has yellow color expression at coleoptile emergence that does not persist beyond the seedling stage, is homozygous-viable, and is non-lethal with no apparent deleterious effects. The Yg3 mutation has potential as a haploid inducer marker in exotic germplasm and small breeding programs where the use of R1-Navajo and high oil inducers is not feasible. The yg3 gene maps to 173-175Mb (AGPv3) on chromosome 5, which does not coincide with any previously characterized yg mutant. Transcriptome profiling identified GRMZM2G165521 as a candidate gene that could underlie the mutant phenotype. GRMZM2G165521 is a predicted PPR protein involved in RNA editing and is orthologous to some mutants in rice that also condition ‘yg’ phenotypes. Sequencing of GRMZM2G165521 in the Yg3 background reveals a seven base pair insertion in the first intron relative to the wild-type reference line. This insertion results in an alternate transcription start site and open reading frame that eliminates the first exon of the PPR protein. The alignment of heterozygous yg3 RNAseq reads confirm transcription at the site of the insertion

Identifying In Situ Conservation Priorities for Teosinte

I evaluated phenotypic variation and geographic distributions to assess status and conservation needs among Zea diploperennis, Zea perennis, Zea luxurians, Zea nicaraguensis, and Zea mays (teosinte) populations. My research mapped previously surveyed teosinte populations in arcGIS and analyzed them by average nearest neighbor analysis. Results indicate a highly clustered pattern (p\u3c0.01) of spatial distribution. Principle component analysis of phenotypic variation reveals three linear combinations of traits that account for 87% of the total variation observed. I compared historical to modern distributions and abundances of teosinte to assess population status and conservation needs. Expert observations report that all populations are in decline, but with varying degree. My research addresses the importance of the rapid evolution and introgressive hybridization found in Zea mays L. spp. mays & Zea mays spp. mexicana by field observation and seed collection in San Filipe and Boyeras, Texcoco, Mexico. I hypothesize that teosinte x maize introgression provides a mechanism for genomic diversity and phenotypic variation found in Zea species. Highlighting introgression as an important process would add value to the protection of wild, weedy teosinte populations. Teosinte urgently requires increased in situ conservation efforts

Utilizing maize genomics for pre-breeding insights

Tropospheric ozone (O3) is estimated to cause billions of dollars in global crop losses, but few studies have investigated the effects of elevated O3 on growth and development of C4 crop plants. Free Air Concentration Enrichment (FACE) field experiments were used to evaluate the response of diverse maize inbred and hybrid lines under elevated O3 concentrations ([O3]). Lines were scored for flowering phenology and ear architecture traits. A multi-year analysis showed inconsistent effects of O3 on development. Hybrid ear length and diameter and inbred ear length were all significantly reduced under elevated [O3] compared to ambient conditions. Knowledge about the identity and location of agriculturally important quantitative trait loci (QTL) provides the basis for marker assisted selection in breeding programs. B73 and Mo17 Nearly Isogenic Lines (NILs) were evaluated at the FACE facility for leaf damage and QTL were mapped. In Mo17 NILs, a significant leaf damage QTL was identified on chromosome 2 at ~161 Mb (AGPv3). Results show that B73 introgressions into Mo17 in this region made NILs more susceptible. Leaf damage scores from the field in 2016 and 2017 had a strongly significant correlation (r = 0.93). Field and growth chamber results best fit is non-linear. It appears chambers can identify damage versus no-damage, but not a continuous degree of damage as seen in the field. This indicates the potential for higher-throughput phenotyping and fine mapping of early season O3 damage QTL in a controlled environment. Sensitive and tolerant NILs were identified. Co-dominant insertion/deletion markers flanking the QTL interval were designed and validated in parents and hybrids. This research supplies the resources for future experiments that combine growth chamber phenotyping and genetic fine-mapping to determine the gene(s) underlying this QTL for O3 tolerance. Current doubled haploid (DH) inducer markers are inefficient and have a higher probability of misclassification when used for classification of tropical germplasm. Yg3-N1582, a rare dominant mutant obtained from ethyl methanesulfonate (EMS) mutagenesis, has not been previously mapped. Phenotypically, Yg3-N1582 has yellow color expression at coleoptile emergence that does not persist beyond the seedling stage, is homozygous-viable, and is non-lethal with no apparent deleterious effects. The Yg3 mutation has potential as a haploid inducer marker in exotic germplasm and small breeding programs where the use of R1-Navajo and high oil inducers is not feasible. The yg3 gene maps to 173-175Mb (AGPv3) on chromosome 5, which does not coincide with any previously characterized yg mutant. Transcriptome profiling identified GRMZM2G165521 as a candidate gene that could underlie the mutant phenotype. GRMZM2G165521 is a predicted PPR protein involved in RNA editing and is orthologous to some mutants in rice that also condition ‘yg’ phenotypes. Sequencing of GRMZM2G165521 in the Yg3 background reveals a seven base pair insertion in the first intron relative to the wild-type reference line. This insertion results in an alternate transcription start site and open reading frame that eliminates the first exon of the PPR protein. The alignment of heterozygous yg3 RNAseq reads confirm transcription at the site of the insertion.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste

Uncovering hidden genetic variation in photosynthesis of field‐grown maize under ozone pollution

Ozone is the most damaging air pollutant to crops, currently reducing Midwest US maize production by up to 10%, yet there has been very little effort to adapt germplasm for ozone tolerance. Ozone enters plants through stomata, reacts to form reactive oxygen species in the apoplast and ultimately decreases photosynthetic C gain. In this study, 10 diverse inbred parents were crossed in a half-diallel design to create 45 F1 hybrids, which were tested for ozone response in the field using free air concentration enrichment (FACE). Ozone stress increased the heritability of photosynthetic traits and altered genetic correlations among traits. Hybrids from parents Hp301 and NC338 showed greater sensitivity to ozone stress, and disrupted relationships among photosynthetic traits. The physiological responses underlying sensitivity to ozone differed in hybrids from the two parents, suggesting multiple mechanisms of response to oxidative stress. FACE technology was essential to this evaluation because genetic variation in photosynthesis under elevated ozone was not predictable based on performance at ambient ozone. These findings suggest that selection under elevated ozone is needed to identify deleterious alleles in the world's largest commodity crop