Abstract
For many plants, regulating lignin content and composition to improve lodging resistance is a crucial issue. Caffeic acid O-methyltransferase (COMT) is a lignin monomer-specific enzyme that controls S subunit synthesis in plant vascular cell walls. Here, we identified 12 BnCOMT1 gene homologues, namely BnCOMT1-1 to BnCOMT1-12. Ten of 12 genes were composed of four highly conserved exons and three weakly conserved introns. The length of intron I, in particular, showed enormous diversification. Intron I of homologous BnCOMT1 genes showed high identity with counterpart genes in Brassica rapa and Brassica oleracea, and intron I from positional close genes in the same chromosome were relatively highly conserved. A phylogenetic analysis suggested that COMT genes experience considerable diversification and conservation in Brassicaceae species, and some COMT1 genes are unique in the Brassica genus. Our expression studies indicated that BnCOMT1 genes were differentially expressed in different tissues, with BnCOMT1-4, BnCOMT1-5, BnCOMT1-8, and BnCOMT1-10 exhibiting stem specificity. These four BnCOMT1 genes were expressed at all developmental periods (the bud, early flowering, late flowering and mature stages) and their expression level peaked in the early flowering stage in the stem. Drought stress augmented and accelerated lignin accumulation in high-lignin plants but delayed it in low-lignin plants. The expression levels of BnCOMT1s were generally reduced in water deficit condition. The desynchrony of the accumulation processes of total lignin and BnCOMT1s transcripts in most growth stages indicated that BnCOMT1s could be responsible for the synthesis of a specific subunit of lignin or that they participate in other pathways such as the melatonin biosynthesis pathway.
Highlights
Rapeseed (Brassica napus L.) is a crucial economic crop worldwide, largely stemming from steady demands for rapeseed oil consumption and biodiesel production
We identified 42 B. napus coding sequences (CDS) representing Caffeic acid O-methyltransferase (COMT) genes (S2 Table) with gene sequence identities higher than 85%
The belonging to the COMT gene family 1 (BnCOMT1) genes were annotated based on the Arabidopsis orthologues with Bn standing for B. napus genes
Summary
Rapeseed (Brassica napus L.) is a crucial economic crop worldwide, largely stemming from steady demands for rapeseed oil consumption and biodiesel production. Concerns over rapeseed production are growing since the agricultural yields of rapeseed are severely restricted by plant lodging and disease, which have even resulted in production declines. The lignification levels of the stem and root in rapeseed closely correlate with plant lodging and wreckage, as lignification influences the rigidity and arrangement of vascular tissues. Lignin is a structural heteropolymer abundant in vascular plants. Lignin provides intercellular hydrophobicity [1] and mechanical support for plant tissues [2] and effectively defends against biotic and abiotic stresses [3]. A proper S/G ratio is beneficial for improving plant resistance to stress
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