@article{heim_ma_willard_shelton_lewis_2021, title={Evaluation of tobacco lines and hybrids carrying Beinhart-1000 alleles at the Phn15.1 locus for agronomic and disease resistance characteristics}, volume={61}, ISSN={["1435-0653"]}, DOI={10.1002/csc2.20520}, abstractNote={Abstract}, number={4}, journal={CROP SCIENCE}, author={Heim, Crystal and Ma, Justin and Willard, Eric and Shelton, Cameron and Lewis, Ramsey S.}, year={2021}, month={Jul}, pages={2456–2466} }
 @article{ma_heim_humphry_nifong_lewis_2020, title={Characterization of Phn15.1, a Newly Identified Phytophthora nicotianae Resistance QTL in Nicotiana tabacum}, volume={104}, ISSN={["1943-7692"]}, DOI={10.1094/PDIS-10-19-2257-RE}, abstractNote={ Phytophthora nicotianae is an oomycete that causes black shank, one of the most economically important diseases affecting tobacco production worldwide. Identification and introgression of novel genetic variability affecting partial genetic resistance to this pathogen is important because of the increased durability of partial resistance over time as compared with genes conferring immunity. A previous mapping study identified a quantitative trait locus (QTL), hereafter designated as Phn15.1, with a major effect on P. nicotianae resistance in tobacco. In this research, we describe significantly improved resistance of nearly isogenic lines (NILs) of flue-cured tobacco carrying the introgressed Phn15.1 region derived from highly resistant cigar tobacco cultivar Beinhart 1000. The Phn15.1 region appeared to act in an additive or partially dominant manner to positively affect resistance. To more finely resolve the position of the gene or genes underlying the Phn15.1 effect, the QTL was mapped with an increased number of molecular markers (single-nucleotide polymorphisms) identified to reside within the region. Development and evaluation of subNILs containing varying amounts of Beinhart 1000-derived Phn15.1-associated genetic material permitted the localization of the QTL to a genetic interval of approximately 2.7 centimorgans. Importantly, we were able to disassociate the Beinhart 1000 Phn15.1 resistance alleles from a functional NtCPS2 allele(s) which contributes to the accumulation of a diterpene leaf surface exudate considered undesirable for flue-cured and burley tobacco. Information from this research should be of value for marker-assisted introgression of Beinhart 1000-derived partial black shank resistance into flue-cured and burley tobacco breeding programs. }, number={6}, journal={PLANT DISEASE}, author={Ma, Justin M. and Heim, Crystal B. and Humphry, Matt and Nifong, Jessica M. and Lewis, Ramsey S.}, year={2020}, month={Jun}, pages={1638–1646} }
 @article{ma_hancock_nifong_kernodle_lewis_2020, title={Identification and editing of a hybrid lethality gene expands the range of interspecific hybridization potential in Nicotiana}, volume={133}, ISSN={["1432-2242"]}, DOI={10.1007/s00122-020-03641-w}, abstractNote={Identification and inactivation of hybrid lethality genes can be used to expand the available gene pool for improvement of a cultivated crop species. Hybrid lethality is one genetic mechanism that contributes to reproductive isolation in plants and serves as a barrier to use of diverse germplasm for improvement of cultivated species. A classic example is the seedling lethality exhibited by progeny from the Nicotiana tabacum × N. africana interspecific cross. In order to increase the body of knowledge on mechanisms of hybrid lethality in plants, and to potentially develop tools to circumvent them, we utilized a transposon tagging strategy to identify a candidate gene involved in the control of this reaction. N. tabacum gene Nt6549g30 was identified to code for a class of coiled-coil nucleotide-binding site-leucine-rich repeat (CC-NBS-LRR) proteins, the largest class of plant defense proteins. Gene editing, along with other experiments, was used to verify that Nt6549g30 is the gene at the N. tabacum Hybrid Lethality 1 (NtHL1) locus controlling the hybrid lethality reaction in crosses with N. africana. Gene editing of Nt6549g30 was also used to reverse interspecific seedling lethality in crosses between N. tabacum and eight of nine additional tested species from section Suaveolentes. Results further implicate the role of disease resistance-like genes in the evolution of plant species and demonstrate the possibility of expanding the gene pool for a crop species through gene editing.}, number={10}, journal={THEORETICAL AND APPLIED GENETICS}, author={Ma, Justin and Hancock, Wesley G. and Nifong, Jessica M. and Kernodle, Sheri P. and Lewis, Ramsey S.}, year={2020}, month={Oct}, pages={2915–2925} }
 @article{ma_heim_humphry_nifong_lewis_2019, title={Genetic analysis of Phn7.1, a major QTL conferring partial resistance to Phytophthora nicotianae in Nicotiana tabacum}, volume={39}, DOI={10.1007/s11032-018-0923-x}, number={1}, journal={MOLECULAR BREEDING}, author={Ma, Justin M. and Heim, Crystal and Humphry, Matt and Nifong, J. M. and Lewis, Ramsey S.}, year={2019} }
 @article{steede_ma_eickholt_drake-stowe_kernodle_shew_danehower_lewis_2017, title={The Tobacco Trichome Exudate Z-abienol and Its Relationship With Plant Resistance to Phytophthora nicotianae}, volume={101}, ISSN={["1943-7692"]}, DOI={10.1094/pdis-10-16-1512-re}, abstractNote={ In previous research, we discovered a favorable quantitative trait locus (QTL) in cigar tobacco cultivar ‘Beinhart 1000’ designated as Phn15.1, which provides a high level of partial resistance to the black shank disease caused by Phytophthora nicotianae. A very close genetic association was also found between Phn15.1 and the ability to biosynthesize Z-abienol, a labdanoid diterpene exuded by the trichomes onto above-ground plant parts, and that imparts flavor and aroma characteristics to Oriental and some cigar tobacco types. Because accumulation of Z-abienol is considered to be undesirable for cultivars of other tobacco types, we herein describe a series of experiments to gain insight on whether this close association is due to genetic linkage or pleiotropy. First, in an in vitro bioassay, we observed Z-abienol and related diterpenes to inhibit hyphal growth of P. nicotianae at concentrations between 0.01 and 100 ppm. Secondly, we field-tested transgenic versions of Beinhart 1000 carrying RNAi constructs for downregulating NtCPS2 or NtABS, two genes involved in the biosynthesis of Z-abienol. Thirdly, we also field tested a recombinant inbred line population segregating for a truncation mutation in NtCPS2 leading to an interrupted Z-abienol pathway. We observed no correlation between field resistance to P. nicotianae and the ability to accumulate Z-abienol in either the transgenic materials or the mapping population. Results suggest that, although Z-abienol may affect P. nicotianae when applied at high concentrations in in vitro assays, the compound has little effect on black shank disease development under natural field conditions. Thus, it should be possible to disassociate Phn15.1-mediated black shank resistance identified in cigar tobacco cultivar Beinhart 1000 from the ability to accumulate Z-abienol, an undesirable secondary metabolite for burley and flue-cured tobacco cultivars. }, number={7}, journal={PLANT DISEASE}, author={Steede, William T. and Ma, Justin M. and Eickholt, David P. and Drake-Stowe, Katherine E. and Kernodle, Sheri P. and Shew, H. David and Danehower, David A. and Lewis, Ramsey S.}, year={2017}, month={Jul}, pages={1214–1221} }