A phosphoinositide map at the shoot apical meristem in Arabidopsis thaliana

Abstract

BackgroundIn plants, the shoot apical meristem (SAM) has two main functions, involving the production of all aerial organs on the one hand and self-maintenance on the other, allowing the production of organs during the entire post-embryonic life of the plant. Transcription factors, microRNA, hormones, peptides and forces have been involved in meristem function. Whereas phosphatidylinositol phosphates (PIPs) have been involved in almost all biological functions, including stem cell maintenance and organogenesis in animals, the processes in meristem biology to which PIPs contribute still need to be delineated.ResultsUsing biosensors for PI4P and PI(4,5)P2, the two most abundant PIPs at the plasma membrane, we reveal that meristem functions are associated with a stereotypical PIP tissue-scale pattern, with PI(4,5)P2 always displaying a more clear-cut pattern than PI4P. Using clavata3 and pin-formed1 mutants, we show that stem cell maintenance is associated with reduced levels of PIPs. In contrast, high PIP levels are signatures for organ-meristem boundaries. Interestingly, this pattern echoes that of cortical microtubules and stress anisotropy at the meristem. Using ablations and pharmacological approaches, we further show that PIP levels can be increased when the tensile stress pattern is altered. Conversely, we find that katanin mutant meristems, with increased isotropy of microtubule arrays and slower response to mechanical perturbations, exhibit reduced PIP gradients within the SAM. Comparable PIP pattern defects were observed in phospholipase A3β overexpressor lines, which largely phenocopy katanin mutants at the whole plant level.ConclusionsUsing phospholipid biosensors, we identified a stereotypical PIP accumulation pattern in the SAM that negatively correlates with stem cell maintenance and positively correlates with organ-boundary establishment. While other cues are very likely to contribute to the final PIP pattern, we provide evidence that the patterns of PIP, cortical microtubules and mechanical stress are positively correlated, suggesting that the PIP pattern, and its reproducibility, relies at least in part on the mechanical status of the SAM.Electronic supplementary materialThe online version of this article (10.1186/s12915-018-0490-y) contains supplementary material, which is available to authorized users.

Xyloglucans and Microtubules Synergistically Maintain Meristem Geometry and Phyllotaxis

“…Arabidopsis (Arabidopsis thaliana) Col-0 and Ws-2 ecotype plants were used as wild type. All mutants and marker lines used in this study have been described previously: xxt1xxt2 (Col-0; Cavalier et al, 2008), xyl1-4 (Col-0; Sechet et al, 2016), bot1-7 (Ws-2; Sassi et al, 2014), ktn1(SAIL_343_D12; Lin et al, 2013), 35S:GFP-MBD (Hamant et al, 2008), 35S:GFP-Lti6b (Sassi et al, 2014), and PDF1:mCitrine-MBD (Stanislas et al, 2018). To obtain xyl1-4 bot1-7 double homozygous plant, the plants were selfed after a first cross and homozygous bot1-7/heterozygous xyl1 plants were selected in the third generation.…”

The Plasma Membrane—An Integrating Compartment for Mechano-Signaling

“…The dynamics of the plasma membrane in response to mechanical stress is still a black spot in plants. In the SAM, PI(4)P and PI(4,5)P 2 distribution at the plasma membrane correlates with the predicted mechanical stress pattern (and thereby cMT organization) [76]. Nevertheless, the exact contribution of anionic phospholipids to cMT distribution or the cell wall integrity pathways still needs to be shown.…”

“…In the boundary between the newly forming organs and the peripheral zone of the meristem, the tissue is folded and mechanical stress is predicted to be highly anisotropic along the axis of the boundary [8]. It was recently shown, using specific biosensors, that two phosphoinositide phosphates, phosphatidylinositol-4-phosphate (PI4P) and phosphatidylinositol-4,5-bisphosphate (PI(4,5)P 2 ), accumulate in the boundary zone of the SAM [76]. Modification of the mechanical stress by tissue ablations and pharmacological approaches induce PI(4,5)P 2 ectopic accumulation that matches the predicted mechanical stress pattern [76].…”

“…It was recently shown, using specific biosensors, that two phosphoinositide phosphates, phosphatidylinositol-4-phosphate (PI4P) and phosphatidylinositol-4,5-bisphosphate (PI(4,5)P 2 ), accumulate in the boundary zone of the SAM [76]. Modification of the mechanical stress by tissue ablations and pharmacological approaches induce PI(4,5)P 2 ectopic accumulation that matches the predicted mechanical stress pattern [76]. These results strongly suggest a relation between phosphoinositide phosphates and cMTs and open the path to explore the role of signaling lipids in mechano-transduction.…”

Xyloglucan homeostasis and microtubule dynamics synergistically maintain meristem geometry and robustness of phyllotaxis in Arabidopsis

“…Arabidopsis thaliana Col-0 and Ws-2 ecotype plants were used as wild-type. All mutants and marker lines used in this study have been described previously: xxt1xxt2 (Cavalier et al, 2008), xyl1-4 (Sechet et al, 2016), bot1-7 (Sassi et al, 2014), ktn1 (Chen et al, 2014), 35S:GFP- MBD (Hamant et al, 2008), 35S:GFP-Lti6b (Sassi et al, 2014) and PDF1:mCitrine-MBD (Stanislas et al, 2018). The other materials were generated by crossing and subsequently confirmed by genotyping.…”