Interspecies Differences in Organ-Specific Expression of the Melatonin Biosynthesis Genes SNAT1 and SNAT2 in the Allium Genus

Homologs of key melatonin biosynthesis genes encoding serotonin N-acetyltransferases SNAT1 and SNAT2 were identified and characterized in the genomes of onion Allium cepa and garlic Allium sativum. Organ-specific expression profiles were determined (in silico, real-time PCR) in plants of the studied species (A. cepa cultivar, A. cepa var. aggregatum accession, four A. sativum cultivars, and two A. sativum accessions). Expression of both genes was highest in leaves; however, the SNAT1/SNAT2 transcript level ratio varied depending on both the Allium species (A. cepa/A. cepa var. aggregatum/A. sativum) and the cultivar/accession within the species. Expression of AcSNAT1 was found to be almost an order of magnitude higher than that of AsSNAT1. Unlike AsSNAT2, which was expressed only in the leaves of A. sativum, its homolog AcSNAT2 was shown to be expressed in all analyzed organs of A. cepa plants, but at a lower level than AcSNAT1.