Lothar Kalmbach studied biology at the Universities of Mainz, Umeå and Würzburg. After his Diploma thesis with Markus Grebe (2010) he joined the lab of Niko Geldner in Lausanne for his PhD thesis (2010-2016) working on the cellular processes underlying Casparian Strip formation in the endodermis. He left Lausanne for a postdoc in Cambridge as a Marie-Curie, SNSF and EMBO Fellow in Yka Helariutta’s lab where he studied phloem development and cellular differentiation (2016-2022). He then accepted a junior group leader position in the department of Jürgen Kleine-Vehn in Freiburg (2023-2024). After being awarded a Starting Grant from the Swiss National Science Foundation, he started his lab as an Assistant Professor in Neuchâtel in 2024. 

We investigate how plants transport essential organic molecules to support growth, development and signaling across distant tissues. Our work spans multiple scales from the sub-cellular to the whole organism level, combining advanced microscopy, functional genetics, synthetic biology, and physiological approaches.

The plant vascular system consists of xylem and phloem, with the former transporting water and inorganic nutrients from the root to the shoot, and the phloem transporting organic nutrients, such as sugars and amino acids from photosynthetically active “source” tissues like leaves to photosynthetically inactive “sink” tissues like roots and fruits.

At the heart of phloem transport are “sieve elements” - specialized cells that unlike xylem vessels, remain alive but undergo substantial internal restructuring. These cells feature “sieve pores”, large cytosolic connections in the cell wall, connecting neighboring sieve elements through a perforated cell wall called “sieve plate”. With diameters ranging from 0.2 to 5.0 µm, sieve pores are considerably larger than plasmodesmata (10 to 250 times larger) or animal gap junctions (100 to 5000 times larger). The combination of a drastically reduced cellular content and the large connecting sieve pores make sieve elements exceptionally adapted to high-volume symplastic (i.e. intracellular) transport as opposed to the apoplastic (i.e. extracellular) transport that occurs in the dead xylem vessels. To build the large sieve pores, sieve elements undergo a profound remodeling of their cell wall that includes the deposition and degradation of callose (Barratt et al., 2011, Kalmbach & Helariutta 2019, Kalmbach et al., 2023) and pectin (Kalmbach et al., 2023). On the other hand, constrictions of sieve pores, either due to developmental defects or biotic and abiotic stressors, can have drastic physiological consequences.

Our research explores how these cell wall remodeling processes are orchestrated, executed, and fine-tuned during phloem development and how changes in cell wall architecture can influence phloem transport and ultimately plant growth and development. Key questions we address include how callose is locally deposited and degraded and how pectin is remodeled in a tissue-specific context. Callose is a rare but highly localized cell wall polymer in plant cell walls, that forms rings around sieve pores and whose deposition there appears to be critical to form large, highly conductive pores between sieve elements. Here, we aim to understand how callose biosynthetic enzymes are recruited and anchored in defined plasma membrane micro-domains and regulated in a phloem-specific context. Pectin on the other hand is highly abundant in cell walls. We recently showed that tissue-specific pectin degradation is necessary for normal sieve element development and function. Pectin degradation changes cell wall architecture but also releases breakdown products that can act as potent elicitors of cell wall signaling. We are now investigating further sieve-element-specific pectin modifications and their effects on phloem function and whether pectin degradation influences both cell wall architecture and signaling mechanisms triggered by the production of pectin breakdown products.

Our research aims to deepen our understanding of vascular function in plants and how tissue-specific cell wall modifications influence their physiology to distribute vital resources efficiently enabling growth and adaptation in various environments. 

Rößling AK, Dünser K, Liu C, Lauw S, Rodriguez-Franco M, Kalmbach L, Barbez E, Kleine-Vehn J. Pectin methylesterase activity is required for RALF1 peptide signalling output. Elife. 2024 Oct 3;13. doi: 10.7554/eLife.96943. PubMed PMID: 39360693; PubMed Central PMCID: PMC11449480. 

Kalmbach L, Bourdon M, Belevich I, Safran J, Lemaire A, Heo JO, Otero S, Blob B, Pelloux J, Jokitalo E, Helariutta Y. Putative pectate lyase PLL12 and callose deposition through polar CALS7 are necessary for long-distance phloem transport in Arabidopsis. Curr Biol. 2023 Mar 13;33(5):926-939.e9. doi: 10.1016/j.cub.2023.01.038. Epub 2023 Feb 16. PubMed PMID: 36805125. 

De Bellis D, Kalmbach L, Marhavy P, Daraspe J, Geldner N, Barberon M. Extracellular vesiculo-tubular structures associated with suberin deposition in plant cell walls. Nat Commun. 2022 Mar 18;13(1):1489. doi: 10.1038/s41467-022-29110-0. PubMed PMID: 35304458; PubMed Central PMCID: PMC8933581. 

Kalmbach L, Helariutta Y. Sieve Plate Pores in the Phloem and the Unknowns of Their Formation. Plants (Basel). 2019 Jan 22;8(2). doi: 10.3390/plants8020025. Review. PubMed PMID: 30678196; PubMed Central PMCID: PMC6409547. 

Kalmbach L, Hématy K, De Bellis D, Barberon M, Fujita S, Ursache R, Daraspe J, Geldner N. Transient cell-specific EXO70A1 activity in the CASP domain and Casparian strip localization. Nat Plants. 2017 Apr 24;3:17058. doi: 10.1038/nplants.2017.58. PubMed PMID: 28436943. 

Li B, Kamiya T, Kalmbach L, Yamagami M, Yamaguchi K, Shigenobu S, Sawa S, Danku JM, Salt DE, Geldner N, Fujiwara T. Role of LOTR1 in Nutrient Transport through Organization of Spatial Distribution of Root Endodermal Barriers. Curr Biol. 2017 Mar 6;27(5):758-765. doi: 10.1016/j.cub.2017.01.030. Epub 2017 Feb 23. PubMed PMID: 28238658. 

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