Sorting nexins, a component of retromer complex, interact with SRK in Brassica oleracea

Abstract

Flowering plants have evolved self-incompatibility (SI) system to reject self-pollination and promote outcrossing. To further excavate SI molecular factors in Brassica oleracea, we screened pistil protein profiles. One protein spot was identified as SNX2b (sorting nexin protein 2b), which was down-regulated when expressed in cross-pollinated pistil. After cloning and sequencing SNX2b and its homologous SNX1 (sorting nexin protein 1) and SNX2a (sorting nexin protein 2a) in B. oleracea, we found that all of them contain a PX domain in N-terminal. Compared to BoSNXs (sorting nexin proteins) expression levels in reproductive organs, we found that, BoSNX1 and BoSNX2a were highly expressed in anther; however, BoSNX2b was highly expressed in pistil. qRT-PCR assays revealed that BoSNX1 and BoSNX2a showed similar expression pattern and BoSNX2b showed different expression pattern in both self- and cross-pollination process. In yeast two-hybrid assays, BoSNX1, BoSNX2a, and BoSNX2b interacted with BoSRKj (S-locus receptor kinase protein, kinase domain). Taken together, our results demonstrated that BoSNX1, BoSNX2a and BoSNX2b were differentially expressed in flower organs and in the early pollination process. On the other hand, BoSNX1, BoSNX2a, and BoSNX2b interacted with BoSRKj. Taking together, it can be suggested that BoSNX1 and BoSNX2a share similar functions but BoSNX2b plays a different role in SI response.