Identification of Chalcone Synthase Genes from Garlic (Allium sativum L.) and Their Expression Levels in Response to Stress Factors.

Abstract

A plant's defense response involves the accumulation of flavonoids, whose biosynthetic pathway in garlic Allium sativum L. remains not characterized. In this work, we identified eight AsCHS1-8 genes of chalcone synthases in the A. sativum genome which presumably catalyze the first stage of flavonoid synthesis in garlic plants. These genes were found to be localized on 4 chromosomes: AsCHS2, 6-8 contain 1 to 2 introns, whereas AsCHS1, 3-5 are intronless. The analysis of the organ-specific gene expression profiles revealed significant transcript levels for AsCHS3 and 8. Only AsCHS8 was shown to change its expression level in response to abiotic stressors (salinity, drought, cold) and exogenous phytohormones (abscisic acid, methyl jasmonate). These findings suggest that two out of the eight genes, AsCHS3 and 8, control flavonoid synthesis during garlic development, with AsCHS8 being the most active chalcone synthase gene. The other six genes (AsCHS1, 2, 4-7) may be involved in flavonoid biosynthesis in highly specialized cells/tissues/organs or the developmental stages of the garlic plant. Our results on the identification and characterization of garlic chalcone synthase genes AsCHS1-8 may facilitate further analysis of the mechanisms that regulate stress adaptation in A. sativum and other Allium species. A plant's defense response involves the accumulation of flavonoids, whose biosynthetic pathway in garlic Allium sativum L. remains not characterized. In this work, we identified eight AsCHS1-8 genes of chalcone synthases in the A. sativum genome which presumably catalyze the first stage of flavonoid synthesis in garlic plants. These genes were found to be localized on 4 chromosomes: AsCHS2, 6-8 contain 1 to 2 introns, whereas AsCHS1, 3-5 are intronless. The analysis of the organ-specific gene expression profiles revealed significant transcript levels for AsCHS3 and 8. Only AsCHS8 was shown to change its expression level in response to abiotic stressors (salinity, drought, cold) and exogenous phytohormones (abscisic acid, methyl jasmonate). These findings suggest that two out of the eight genes, AsCHS3 and 8, control flavonoid synthesis during garlic development, with AsCHS8 being the most active chalcone synthase gene. The other six genes (AsCHS1, 2, 4-7) may be involved in flavonoid biosynthesis in highly specialized cells/tissues/organs or the developmental stages of the garlic plant. Our results on the identification and characterization of garlic chalcone synthase genes AsCHS1-8 may facilitate further analysis of the mechanisms that regulate stress adaptation in A. sativum and other Allium species.