Long noncoding miRNA gene represses wheat β-diketone waxes

Area of Science:

• Plant biology
• Genetics
• Molecular biology

Background:

• The epicuticular wax layer in terrestrial plants, particularly the β-diketone waxes in wheat (Triticeae), confers a glaucous (bluish-white) appearance.
• Glaucousness in durum wheat is regulated by the WAX1 (W1) locus and a suppressor, INHIBITOR of WAX1 (Iw1), on chromosome 2B, with paralogs W2 and Iw2 on chromosome 2D in the D subgenome.

Purpose of the Study:

• To identify the Iw1 gene in durum wheat and elucidate its unique regulatory mechanism.
• To investigate the role of Iw1 and its derived microRNA (miRNA) in controlling the glaucous phenotype and β-diketone wax biosynthesis.

Main Methods:

• Identification and characterization of the Iw1 gene, a long noncoding RNA (lncRNA).
• Analysis of the Iw1 transcript structure, including its inverted repeat (IR) region and miRNA precursor-like hairpin.
• Functional analysis by introducing Iw1 into glaucous bread wheat to observe phenotypic and molecular changes.

Main Results:

• Iw1 was identified as a lncRNA with an IR region highly homologous to W1-COE, suppressing W1-COE expression.
• Iw1 produces a predominant 21-nt miRNA, miRW1, associated with the nonglaucous phenotype.
• Introduction of Iw1 into glaucous wheat resulted in miRW1 accumulation, down-regulation of W1-COE and W2-COE, and a nonglaucous, wax-depleted phenotype.

Conclusions:

• The Iw1 gene employs a novel regulatory mechanism involving lncRNA-derived miRNA to suppress wax biosynthesis.
• The Iw loci likely originated from inverted duplications of W1-COE/W2-COE, representing evolutionarily young miRNA genes that repress the glaucous trait in wheat.