N-terminal domains of ARC1 are essential for interaction with the N-terminal region of Exo70A1 in transducing self-incompatibility of <italic>Brassica oleracea</italic>

Abstract

Self-incompatibility (SI) is an important mating system to prevent inbreeding and promote outcrossing. ARC1 and Exo70A1 function as the downstream targets of the S-locus receptor kinase and play conservative roles in Brassica SI signaling. Based on the sequence homology, Exo70A1 is divided into four subdomains: leucine zipper (Leu are required for the interaction with Exo70A1, while the addition of ARM motif results in loss of the interaction with Exo70A1. Meanwhile, the N-terminal of Exo70A1 without any domains shows a weak interaction with ARC1, and the level of LacZ expression increases with addition of leucine zipper and reaches the maximum value with hypervariable region and SUMO modification motif, indicating that hypervariable region and SUMO modification motif of Exo70A1 172-275 is mainly responsible for the binding with ARC1, whereas pfamExo70 domain has little affinity for ARC1. Lys 181 located in the Exo70A1 hypervariable region may be the ubiquitination site mediating the interaction between ARC1 and Exo70A1. Therefore, both the leucine zipper with coiled-coil structure of ARC1 , and the hypervariable region and SUMO modification motif of Exo70A1 are the core interaction domains between ARC1 and Exo70A1. Any factors affecting these core domains would be the regulators of ARC1 mediating ubiquitin degradation in self-incompatible system.

EbARC1, an E3 Ubiquitin Ligase Gene in Erigeron breviscapus, Confers Self-Incompatibility in Transgenic Arabidopsis thaliana

“…Further analysis showed that EbARC1 interacted with Exo70A1 ( Figure 6). The same study in Brassica also indicated that ARC1 interacts with Exo70A1, and the ARC1-Ubox domain and the N-terminal of Exo70A1 are the key regions for the interaction [16,39,40], which is consistent with our results ( Figure 6). Exo70A1 is a compatibility factor that is required for normal germination and growth of pollen [41].…”

Gene editing in Brassica napus for basic research and trait development

“…Before pollination, the expression of the SRK and arm repeat containing 1 (ARC1), an E3 ubiquitin ligase, were suppressed in the Bnamlpk quadruple mutant disrupting SI signal transduction to enable pollen tube growth and elongation. Both MLPK and ARM1 are positive regulators that are known to interact with SRK in the SI pathway (Shi et al 2016). By comparison, the self-compatible factor GLO1 was slightly induced in the Bnamlpk quadruple mutant (Chen et al 2019).…”