Genetic Diversity in Members of the Z. mays Lipoxygenase Gene Family and its Utility in Association Mapping for Drought Tolerance and Aflatoxin Resistance

Maize (Zea mays) production in the southern United States routinely suffers from abiotic stress caused by drought and biotic stress caused by the soil borne fungus, Aspergillus flavus, which produces a carcinogenic mycotoxin known as aflatoxin.  The maize lipoxygenase gene family, well known for its role in plant defense, contains a set of 13 individual members. It is hypothesized that individual LOX genes have unique physiological functions due to their specialization in biosynthesis of functionally diverse oxylipins. When considering sequence homology, the two most related members of the 13 are ZmLOX4 and ZmLOX5, which share 94% identity. Studies conducted with knockout mutant NILs for ZmLOX4 and ZmLOX5 show evidence that ZmLOX4 conditions increased tolerance to drought stress and ZmLOX5 conditions increased resistance to field contamination from aflatoxin.  These mutant NIL were testcrossed onto 300 inbred lines of a maize association panel in which we sequenced ZmLOX4 and ZmLOX5 loci in search of natural allelic diversity.  Sequence data for these two loci were analyzed and SNPs were found at both loci and one INDEL was found in LOX5 that appears to shift the reading frame.  Sequence data was used to create haplotypes and characterize the diversity, and to look at the linkage disequilibrium structure around these loci.  Testcross hybrids were grown in a yield trial where controlled drought stress and aflatoxin inoculation were used to evaluate the utility of these new alleles for drought tolerance and aflatoxin resistance.