Sieve elements. Hidden corners, fierce debates, future prospects

Abstract Sieve elements (SEs) represent one of the most specialized cell types in plants, yet several fundamental aspects of their structure, regulation, and physiological integration remain incompletely understood. Despite recent advances that refined our understanding of SE function, persistent questions and controversies remain concerning key aspects of SE biology, such as the disputed presence of a proteolytic machinery and a cytoskeleton, the functions of plastids and mitochondria, the role