Genome-wide analysis of the COMT gene family in Avena sativa: insights into lignin biosynthesis and disease defense mechanisms

Abstract

Caffeic acid O-methyltransferase (COMT) is a multifunctional enzyme involved in lignin biosynthesis and plays an important role in various primary and secondary metabolic pathways, including the plant stress response. In this study, we identified 37 AsCOMT genes from the oat (Avena sativa) whole-genome database, which are distributed across 11 chromosomes. Phylogenetic analysis grouped these genes into two major subfamilies, indicating that they are highly conserved during evolution and share close relationships with COMT genes from Zea mays and Oryza sativa. Cis-acting elements analysis revealed a rich presence of regulatory motifs related to plant hormone signaling and stress responses. Expression profiling of different oat varieties infected with powdery mildew and leaf spot disease showed significant upregulation or downregulation of several AsCOMT genes (e.g., AsCOMT14, AsCOMT22, AsCOMT24, AsCOMT27). Moreover, disease-resistant oat varieties have higher lignin contents compared to susceptible varieties. Overexpression of AsCOMT23 and AsCOMT27 in tobacco leaves resulted in significantly increased lignin content, highlighting the potential of these genes in lignin biosynthesis. These results offer a preliminary exploration of the role of AsCOMT in both lignin synthesis and the plant stress response, laying the groundwork for further functional studies and potential applications in oat breeding.

Keywords: bioinformatics analysis; caffeic acid o-methyltransferase; expression pattern; lignin biosynthesis; plant disease defense.

Figure 1

Distribution of AsCOMTs genes across oat chromosomes. Blue bars represent the nine chromosomes that contain AsCOMT genes. The scale indicates the length of each chromosome, and the black lines mark the position of each AsCOMT gene. The green bars in the figure represent the 11 chromosomes containing the AsCOMT gene, with the blue text above indicating the chromosome names; the black lines mark the position of each AsCOMT gene. The scale on the left side of the figure indicates the chromosome length in Mb, allowing for the inference of the relative positions and intervals between the genes.

Figure 2

Conserved motif diagram of oat AsCOMT proteins. (A) Conserved motif analysis of AsCOMT family proteins; (B) Conservative structural domain analysis; (C) Gene structure analysis.

Figure 3

Phylogenetic analysis of COMT protein sequences in oat, A. thaliana, O. sativa and Z. mays. Oat AsCOMT proteins are marked with stars.

Figure 4

The cis-acting regulatory elements contained in the 2 kb promoter regions of the AsCOMT genes. (A) A phylogenetic tree was reconstructed using the full-length sequences of AsCOMT proteins, with different color backgrounds representing different groupings. (B) The distributions of cis-regulatory elements within the promoter regions of the AsCOMT genes, with different colored boxes representing different functional elements. (C) Statistics on the number of cis-acting elements of the AsCOMT genes. The numbers in the heat map box indicate the number of identified elements, while empty boxes indicate that no corresponding elements were identified.

Figure 5

The synteny blocks of COMT genes in oat. Analysis of intrachromosomal fragment duplication of COMT genes in the oat genome. The grey lines represent all synteny blocks, while the red lines specially highlight the duplicated pairs among the 37 AsCOMT genes.

Figure 6

The predicted interaction network of AsCOMT proteins based on interactions of their orthologs in O. sativa (Japonica).

Figure 7

Expression of AsCOMT genes in two oat cultivars, ‘ForagePlus’ and ‘Molasses’, following infection with Powdery mildew. Significant differences are indicated by asterisks (*p < 0.05, **p < 0.01).

Figure 8

Expression of AsCOMT genes in two oat cultivars, ‘ForagePlus’ and ‘Molasses’, following infection with leaf spot. Significant differences are indicated by asterisks (*p < 0.05, **p < 0.01).

Figure 9

Lignin content dynamics in oat leaves under powdery mildew and leaf spot stress.

Figure 10

Correlation analysis between the lignin content and the expression of AsCOMT genes. (A) The oat variety ‘Molasses’ infected with powdery mildew, (B) the oat variety ‘ForagePlus’ infected with powdery mildew, (C) the oat variety ‘Molasses’ infected with leaf spot, (D) the oat variety ‘ForagePlus’ infected with leaf spot.

Figure 11

Tobacco leaves transiently expressing AsCOMT23 and AsCOMT27 (A) and its lignin content (B). (A) The left image shows the state of tobacco leaves after infection under normal light conditions, while the right image shows the state of tobacco leaves after infection under fluorescent light. The diagonal line indicates that the upper part was not injected with Agrobacterium, while the lower part was injected with Agrobacterium; (B) Changes in lignin content in tobacco leaves after 7 and 9 days of transient expression (**p < 0.01).