title: Differential transcriptional activity of SAD, FAD2 and FAD3 desaturase genes in developing seeds of linseed contributes to varietal variation in α-linolenic acid content.
abstract: Linseed or flax (Linum usitatissimum L.) varieties differ markedly in their seed α-linolenic acid (ALA) levels. Fatty acid desaturases play a key role in accumulating ALA in seed. We performed fatty acid (FA) profiling of various seed developmental stages of ten Indian linseed varieties including one mutant variety. Depending on their ALA contents, these varieties were grouped under high ALA and low ALA groups. Transcript profiling of six microsomal desaturase genes (SAD1, SAD2, FAD2, FAD2-2, FAD3A and FAD3B), which act sequentially in the fatty acid desaturation pathway, was performed using real-time PCR. We observed gene specific as well as temporal expression pattern for all the desaturases and their differential expression profiles corresponded well with the variation in FA accumulation in the two groups. Our study points to efficient conversion of intermediate FAs [stearic (SA), oleic (OA) and linoleic acids (LA)] to the final product, ALA, due to efficient action of all the desaturases in high ALA group. While in the low ALA group, even though the initial conversion up to OA was efficient, later conversions up to ALA seemed to be inefficient, leading to higher accumulation of OA and LA instead of ALA. We sequenced the six desaturase genes from the ten varieties and observed that variation in the amino acid (AA) sequences of desaturases was not responsible for differential ALA accumulation, except in the mutant variety TL23 with very low (<2%) ALA content. In TL23, a point mutation in the FAD3A gene resulted into a premature stop codon generating a truncated protein with 291 AA.
authors.affiliation: Biochemical Sciences Division, CSIR-National Chemical Laboratory, Pune 411 008, India. Electronic address: a.rajwade@ncl.res.in.
authors.forename: Ashwini V
authors.initials: AV
authors.lastname: Rajwade
authors.affiliation: Biochemical Sciences Division, CSIR-National Chemical Laboratory, Pune 411 008, India. Electronic address: ny.kadoo@ncl.res.in.
authors.forename: Narendra Y
authors.initials: NY
authors.lastname: Kadoo
authors.affiliation: Organic Chemistry Division, CSIR-National Chemical Laboratory, Pune 411 008, India. Electronic address: sp.borikar@ncl.res.in.
authors.forename: Sanjay P
authors.initials: SP
authors.lastname: Borikar
authors.affiliation: Interactive Research School for Health Affairs, Bharati Vidyapeeth University, Pune 411 043, India. Electronic address: aharsulkar@gmail.com.
authors.forename: Abhay M
authors.initials: AM
authors.lastname: Harsulkar
authors.affiliation: AICRP on Linseed, College of Agriculture, Nagpur 440 001, India. Electronic address: pbghorpade@rediffmail.com.
authors.forename: Prakash B
authors.initials: PB
authors.lastname: Ghorpade
authors.affiliation: Biochemical Sciences Division, CSIR-National Chemical Laboratory, Pune 411 008, India. Electronic address: vs.gupta@ncl.res.in.
authors.forename: Vidya S
authors.initials: VS
authors.lastname: Gupta
mesh_terms: D044943:Fatty Acid Desaturases / Q000235:genetics* / Q000378:metabolism; D019597:Flax / Q000235:genetics* / Q000254:growth & development; D014644:Genetic Variation / Q000235:genetics*; D008969:Molecular Sequence Data; D012639:Seeds / Q000235:genetics* / Q000254:growth & development; D014158:Transcription, Genetic / Q000235:genetics*; D017962:alpha-Linolenic Acid / Q000235:genetics*
chemical_list: D017962:alpha-Linolenic Acid; D044943:Fatty Acid Desaturases
keywords: ALA; Fatty acid desaturases; Fatty acids; Flax; Gene expression; Linseed