720 / 2019-05-09 14:08:47

Pathways and flight paths in root protophloem differentiation

growth,development,root,phloem,auxin,brassinosteroid

Growth and Development > Growth and Development

Angiosperms dominate terrestrial ecosystems and are characterized by extensive vascular networks, which permit nutrient distribution as well as systemic coordination of physiology and development. In the context of vascular differentiation, the development of phloem sieve elements is particularly interesting, because during their differentiation, sieve elements reduce some organelles and lose others (notably the nucleus) as they interconnect via sieve plates to form continuous sieve tubes. Thus, sieve elements represent a unique cell type that retains complex functionality in the absence of a nucleus. The Arabidopsis root is particularly well-suited to investigate this peculiar differentiation process, because vascular tissues are continuously formed from stem cells at its tip and phloem formation can be followed along the spatio-temporal gradient of single cell files. We have identified an extensive molecular genetic network that governs the differentiation of sieve element precursors. This network comprises angiosperm-specific positive regulators, which drive sieve element differentiation through tipping a delicate quantitative balance, opposing negative regulators of the process. Both auxin transport regulation and brassinosteroid signaling are key aspects of the positive regulatory output, whereas CLE peptide signaling is central to the negative regulatory output. I will present data that illustrate how these pathways intersect to guide sieve element differentiation.