Auxin-controlled tip growth regulation in Arabidopsis thaliana
16 April 2018
Campus Drie Eiken, O.05 - Universiteitsplein 1 - 2610 Antwerpen-Wilrijk (route: UAntwerpen, Campus Drie Eiken
Organization / co-organization:
Department of Biology
PhD defence Sébastjen Schoenaers - Faculty of Science, Department of Biology
Since the colonization of land, plants have evolved strategies that allow them to face the challenges associated with a highly variable and heterogeneous surrounding. Tip growth, a highly specialized and conserved type of polarized cell expansion, is one such strategy. Today, it lies at the basis of root hair (RH) and pollen tube (PT) elongation in multiploid (≥2n) plant species. RHs facilitate a plant’s ability to acquire soil anchorage, nutrients, water and interact with soil microbiota. PTs on the other hand, emerge from the male gametophyte (pollen grain) and facilitate targeted transport and delivery of the sperm cells for double fertilization. As such, tip growth lies at the basis of successful soil exploitation and reproduction, both crucial processes for plant survival.
Decades of research have focussed on better understanding the molecular processes that regulate the different stages of RH and PT development. Nevertheless, several questions have remained unanswered. The hormone auxin is known to function as an organizing centre throughout RH development, and initial evidence suggests a role for auxin in PT development too. However, an in-depth understanding of auxin-controlled processes and targets across the apical cell expansion network is lacking. In addition, little is known on the identity of common RH/PT regulators and how they mechanistically control cell expansion.
To gain an integrated mechanistic insight into how auxin regulates RH development and which regulatory components are conserved amongst PT and RH growth, we characterized (1) ARF7/19-dependent auxin-regulated control of gene transcription across all stages of RH development, (2) the involvement of the ARF7/ARF19-controlled kinase ERULUS in RH and PT tip growth and (3) the role of the ARF19-controlled kinase PERSEUS in the pre-tip growth bulging stage of RH and PT morphogenesis. Our findings illustrate that the intertwinement of auxin throughout all stages of RH development has been heavily underestimated. In addition, our results illustrate (1) a central role for the plasma membrane localized kinase ERULUS in the control of cell wall dynamics and calcium signaling during RH and PT tip growth and (2) an important role for the cytoplasmic/nuclear localized kinase PERSEUS in the control of RH bulge formation and PT emergence.
Collectively, our data identify auxin as a central player in apical cell growth regulation, and illustrate the interconnectivity and diversity of the molecular processes through which RH and PT development are regulated.