Ion and lipid signaling in apical growth—a dynamic machinery responding to extracellular cues

Abstract

Apical cell growth seems to have independently evolved throughout the major lineages of life. To a certain extent, so does our body of knowledge on the mechanisms regulating this morphogenetic process. Studies on pollen tubes, root hairs, rhizoids, fungal hyphae, even nerve cells, have highlighted tissue and cell specificities but also common regulatory characteristics (e.g., ions, proteins, phospholipids) that our focused research sometimes failed to grasp. The working hypothesis to test how apical cell growth is established and maintained have thus been shaped by the model organism under study and the type of methods used to study them. The current picture is one of a dynamic and adaptative process, based on a spatial segregation of components that network to achieve growth and respond to environmental (extracellular) cues. Here, we explore some examples of our live imaging research, namely on cyclic nucleotide gated ion channels, lipid kinases and syntaxins involved in exocytosis. We discuss how their spatial distribution, activity and concentration suggest that the players regulating apical cell growth may display more mobility than previously thought. Furthermore, we speculate on the implications of such perspective in our understanding of the mechanisms regulating apical cell growth and their responses to extracellular cues.

A role for diacylglycerol kinase 4 in signalling crosstalk during Arabidopsis pollen tube growth

“…The guanylyl cyclase domain of DGK4 has also been suggested to modulate NO responses (Wang et al ., ; Wong et al ., ), thus providing a link between NO and Ca 2+ signalling. Both second messengers are involved in tube guidance (Domingos et al ., ; Malhó et al ., ), and our data support such a hypothesis with dgk4 mutant tubes exhibiting altered mechanical properties and reduced ability to target the ovaries. Our qPCR data also showed that dgk4 mutant pollen has downregulation of CAP1, a cyclase‐associated protein in which a mutation was reported to reduce pollen tube length and disrupt actin filaments (Deeks et al ., ).…”

“…). Such fluctuations are consistent with a protein role in signalling networks and secretory events (Odorizzi et al ., ; Malhó et al ., ; Bloch et al ., ).…”

Auxin Regulates Apical Stem Cell Regeneration and Tip Growth in the Marine Red Alga Neopyropia yezoensis

“…The regulatory mechanisms of tip growth have been extensively investigated using root hairs and pollen tubes as single-cell models. These mechanisms involve ion flux, the asymmetric distribution of F-actin, phosphoinositides, membrane trafficking of membrane and cell wall materials, the production of reactive oxygen species, and plant hormones [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ].…”