Abstract
As a crop, flax holds significant commercial value for its omega-3 rich oilseeds and stem fibres. Canada is the largest producer of linseed but there exists scope for significant yield improvements. Implementation of mechanisms such as male sterility can permit the development of hybrids to assist in achieving this goal. Temperature sensitive male sterility has been reported in flax but the leakiness of this system in field conditions limits the production of quality hybrid seeds. Here, we characterized a 2,588 bp transcript differentially expressed in male sterile lines of flax. The twelve intron gene predicted to encode a 368 amino acid protein has five WD40 repeats which, in silico, form a propeller structure with putative nucleic acid and histone binding capabilities. The LuWD40-1 protein localized to the nucleus and its expression increased during the transition and continued through the vegetative stages (seed, etiolated seedling, stem) while the transcript levels declined during reproductive development (ovary, anthers) and embryonic morphogenesis of male fertile plants. Knockout lines for LuWD40-1 in flax failed to develop shoots while overexpression lines showed delayed growth phenotype and were male sterile. The non-viable flowers failed to open and the pollen grains from these flowers were empty. Three independent transgenic lines overexpressing the LuWD40-1 gene had ∼80% non-viable pollen, reduced branching, delayed flowering and maturity compared to male fertile genotypes. The present study provides new insights into a male sterility mechanism present in flax.
Highlights
Male sterility in flax (Linum usitatisimmum L.) was first documented in the early nineteen hundreds from F2 of a cross between a blue flower oilseed type and a white flower fibre type where both parents were hermaphrodite with no male sterility [1]
Sequencing of the cDNA clone LuP1225D10 generated a fragment of 1,638 bp including an 84 bp 59 UTR, a 1,107 bp Open reading frame (ORF) and a 447 bp 39UTR ending in a polyA tail
The genomic clone corresponding to the ORF of LuWD40-1 from the flax whole genome shotgun (WGS) sequence is 4,471 bp and is composed of thirteen exons and twelve introns (Fig. S1B & S1C)
Summary
Male sterility in flax (Linum usitatisimmum L.) was first documented in the early nineteen hundreds from F2 of a cross between a blue flower oilseed type and a white flower fibre type where both parents were hermaphrodite with no male sterility [1]. In the present study we observed the occurrence of male sterility in an F2 cross between oilseed type flax accession Double Low and cultivar AC McDuff. Both Double Low and AC McDuff are fertile parents. We decided to characterize this gene in order to determine its role in male sterility
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