Disruption of the Arabidopsis Acyl-Activating Enzyme 3 impairs seed coat mucilage accumulation and seed germination

Authors: CHENG, NINGHUI - Children'S Nutrition Research Center (CNRC); Nakata, Paul

Submitted to: International Journal of Molecular Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2024
Publication Date: 1/17/2024
Citation: Cheng, N., Nakata, P.A. 2024. Disruption of the Arabidopsis Acyl-Activating Enzyme 3 impairs seed coat mucilage accumulation and seed germination. International Journal of Molecular Sciences. 25(2). Article 1149. https://doi.org/10.3390/ijms25021149.
DOI: https://doi.org/10.3390/ijms25021149

Interpretive Summary: Plant scientists have been avidly working to discover new strategies to increase crop resistance to oxalate-secreting fungal pathogens. These fungal pathogens produce oxalate as a plant toxin that is required by the fungus for plant infection. Such fungi are responsible for major crop losses each year. Previously, we reported the discovery of a novel pathway of oxalate catabolism that helps protect plants from these pathogens. Before strategies can be designed to manipulate this pathway to enhance crop protection, we need to determine whether the enzymes that make up this pathway have other biological roles. In this report, we investigate the role of AAE3, the enzyme catalyzing the first step in this pathway, in seed germination. Staining seeds lacking a functional copy of the AAE3 gene with a dye that stains mucilage (substances that helps seeds germinate) suggested that the observed reduction in seed germination is likely due to a decrease in seed mucilage accumulation. Quantitative RT-PCR analysis revealed that the expression of selected mucilage genes were significantly reduced in the seeds lacking a functional copy of the AAE3 gene. Mucilage accumulation studies using seeds from other oxalate mutants suggested that elevated tissue oxalate concentrations and loss of the oxalate degradation pathway downstream of AAE3 were not responsible for the observed reduction in seed germination and mucilage accumulation. Overall, our findings reveal that AAE3 has more biological roles than just oxalate degradation. One of these roles is in mucilage accumulation which in turn affects seed germination.

Technical Abstract: The Acyl-activating enzyme (AAE) 3 gene encodes an oxalyl-CoA synthetase that catalyzes the conversion of oxalate to oxalyl-CoA as the first step in the CoA-dependent pathway of oxalate catabolism. Although the role of this enzyme in oxalate catabolism has been established, its biological role in plant growth and development is less understood. As a step toward gaining a better understanding of these biological roles, we report here characterization of the Arabidopsis thaliana aae3 (Ataae3) seed germination phenotype. Ruthidium red (RR) staining of Ataae3 and wildtype (WT) seeds suggested that the observed reduction in Ataae3 germination may be attributable, at least in part, to a decrease in seed mucilage accumulation. Quantitative RT-PCR analysis revealed that the expression of selected mucilage regulatory transcription factors, biosynthetic, and extrusion genes were significantly down-regulated in the Ataae3 seeds. Mucilage accumulation by seeds from an engineered oxalate accumulating Arabidopsis and Atoxc mutant, blocked in the second step in the CoA-dependent pathway of oxalate catabolism, were determined to be similar to WT. These findings suggest that elevated tissue oxalate concentrations and loss of the oxalate catabolism pathway downstream of AAE3 were not responsible for the reduced Ataae3 seed germination and mucilage phenotypes. Overall, our findings unveil the presence of regulatory interplay between AAE3 and transcriptional control of mucilage gene expression.