Screening of candidate genes associated with constitutive aerenchyma formation in adventitious roots of the teosinte Zea nicaraguensis

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Zea nicaraguensis (teosinte), a wild relative of maize (Zea mays ssp. mays), constitutively forms aerenchyma, which contributes to plant waterlogging tolerance, in the root cortex in drained soil, whereas maize (inbred line Mi29) does not. One with highest logarithm of odds (LOD) among quantitative trait loci (QTLs) that control constitutive aerenchyma formation in Z. nicaraguensis is Qaer1.05-6 on chromosome 1. Here, we attempted to identify genes in Qaer1.05-6 by comparing cDNA libraries from Mi29, Z. nicaraguensis and a hybrid (BC4F1 #62) carrying Qaer1.05-6. We first confirmed that constitutive aerenchyma formation was apparently observed in the order Z. nicaraguensis > BC4F1 #62 > Mi29. Contigs were assembled from cDNAs pooled from the three lines. We identified 1,868 contigs in the region on chromosome 1 that contained Qaer1.05-6. These contigs were screened for contigs that were predominantly composed of cDNAs from BC4F1 #62 and Z. nicaraguensis (no more than 10% of cDNAs from Mi29). Twenty-one such contigs were found and the genes they encoded were identified. In a real-time reverse transcription-polymerase chain reaction (RT- PCR) analysis, expression of six of these genes in BC4F1 #62 was at least double that in Mi29, making them candidates for genes associated with constitutive aerenchyma formation.