Significance: Storage of lipids in oil bodies (OBs) and their subsequent degradation in response to developmental or environmental cues is a common behavior of eukaryotic cells. In Arabidopsis seeds, the major lipase implicated in OB degradation is Sugar-Dependent 1 (SDP1). We report that lipid storage and degradation are severely impaired in seeds of Arabidopsis mutants altered in the retromer function, a multiprotein complex involved in protein trafficking. We show that SDP1 is initially localized on peroxisomes and then migrates to the OB surface during the course of seedling growth. SDP1 translocation occurs through peroxisomal extensions, and a functional retromer allows timely transfer of SDP1 to OBs. Our work provides unanticipated evidence for the role of peroxisome dynamics in interorganelle communication and protein transport.

Sorting nexins (SNXs) are conserved eukaryotic proteins that associate with three types of vacuolar protein sorting (VPS) proteins to form the retromer complex. How SNXs act in this complex and whether they might work independently of the retromer remains elusive. Here, we show by genetic and cell imaging approaches that the Arabidopsis thaliana SNX1 protein recruits SNX2 at the endosomal membrane, a process required for SNX1-SNX2 dimer activity. We report that, in contrast with the mammalian retromer, SNXs are dispensable for membrane binding and function of the retromer complex. We also show that VPS retromer components can work with or independently of SNXs in the trafficking of seed storage proteins, which reveals distinct functions for subcomplexes of the plant retromer. Finally, we provide compelling evidence that the combined loss of function of SNXs and VPS29 leads to embryo or seedling lethality, underlining the essential role of these proteins in development.

The prevention of fertilization through self-pollination (or pollination by a close relative) in the Brassicaceae plant family is determined by the genotype of the plant at the self-incompatibility locus ( S locus). The many alleles at this locus exhibit a dominance hierarchy that determines which of the two allelic specificities of a heterozygous genotype is expressed at the phenotypic level. Here, we uncover the evolution of how at least 17 small RNA (sRNA)–producing loci and their multiple target sites collectively control the dominance hierarchy among alleles within the gene controlling the pollen S -locus phenotype in a self-incompatible Arabidopsis species. Selection has created a dynamic repertoire of sRNA-target interactions by jointly acting on sRNA genes and their target sites, which has resulted in a complex system of regulation among alleles.