BnaPLDα1-BnaMPK6 Involved in NaCl-Mediated Overcoming of Self-Incompatibility in Brassica napus L.

Self-incompatibility (SI) is an important genetic mechanism exploited by numerous angiosperm species to prevent inbreeding. This mechanism has been widely used in the breeding of SI trilinear hybrids of Brassica napus. The SI responses in these hybrids can be overcome by using a salt (NaCl) solution, which is used for seed propagation in SI lines. However, the mechanism underlying the NaCl-induced breakdown of the SI response in B. napus remains unclear. Here, we investigated the role of two key proteins, BnaPLD alpha 1 and BnaMPK6, in the breakdown of SI induced by NaCl. Pollen grain germination and seed set were reduced in BnaPLD alpha 1 triple mutants following incompatible pollination with NaCl treatment. Conversely, SI responses were partially abolished by overexpression of BnaC05.PLD alpha 1 without salt treatment. Furthermore, we observed that phosphatidic acid (PA) produced by BnaPLD alpha 1 bound to B. napus BnaMPK6. The suppression and enhancement of the NaClinduced breakdown of the SI response in B. napus were observed in BnaMPK6 quadruple mutants and BnaA05. MPK6 overexpression lines, respectively. Moreover, salt-induced stigmatic reactive oxygen species (ROS) accumulation had a minimal effect on the NaCl-induced breakdown of the SI response. In conclusion, our results demonstrate the essential role of the BnaPLD alpha 1-PA-BnaMPK6 pathway in overcoming the SI response to salt treatment in SI B. napus. Additionally, our study provides new insights into the relationship between SI signaling and salt stress response. Significance statement: A new molecular mechanism underlying the breakdown of the NaCl-induced self-incompatibility (SI) response in B. napus has been discovered. It involves the induction of BnaPLD alpha 1 expression by NaCl, followed by the activation of BnaMPK6 through the production of phosphatidic acid (PA) by BnaPLD alpha 1. Ultimately, this pathway leads to the breakdown of SI. The involvement of the BnaPLD alpha 1-PA-BnaMPK6 pathway in overcoming the SI response following NaCl treatment provides new insights into the relationship between SI signalling and the response to salt stress.