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Sequence Analysis of Maize Yellow Stripe3 Candidate Genes

The work presented here focuses on the molecular mechanism of phytosiderophore secretion in graminaceous plants. In maize, yellow stripe3 (ys3) is a mutant that is deficient in its ability to secrete iron-chelating compounds of the mugineic acid family known as phytosiderophores. Phytosiderophores are specific to grasses and are used for the acquisition of iron. Genetic linkage mapping of the ys3 locus lead to a region of interest on chromosome 3 defined by marker UMC1773. The sequence of eleven candidate genes (GRMZM2G390345, GRMZM2G390374, GRMZM2G342821, GRMZM5G800764, GRMZM2G502560, GRMZM5G849435, GRMZM2G105766, GRMZM5G876835, GRMZM2G036976, GRMZM2G502563, miR167g) revealed several small deletions and point mutations within the coding regions of four candidate genes (GRMZM2G390345, GRMZM2G342821, GRMZM2G105766 and GRMZM2G502560). To further investigate these candidate genes, knockout (Mutator) lines were used in an effort to recapitulate the ys3 phenotype. I characterized a GRMZM2G390345 mutant and determined that the mutation in GRMZM2G390345 did not cause the ys3 phenotype. For the three remaining candidate genes, GRMZM2G342821, GRMZM2G105766 and GRMZM2G502560 further analysis is needed. The closest homolog of OsTOM1 (an effluxer of muginieic acid) GRMZM2G603306 which, lies ~7 Mbp outside the linked marker, has also been suggested to be yellow stripe3. Preliminary sequence analysis uncovered a 4 bp insertion within the 9th exon of this gene that shifts the reading frame and leads to a premature stop codon. Three of the genes analyzed remain plausible candidates for yellow stripe3.