Biology subjects

Hardtke, C.

Publications and source records attributed to Hardtke, C..

5 recordsLinked to original sources

bioRxiv2024

The brassinosteroid receptor gene BRI1 safeguards cell-autonomous brassinosteroid signaling across tissues

Brassinosteroid signaling is essential for plant growth as exemplified by the dwarf phenotype of loss-of-function mutants in BRASSINOSTEROID INSENSITIVE 1 (BRI1), a ubiquitously expressed Arabidopsis brassinosteroid receptor gene. Complementation of brassinosteroid-blind receptor mutants by BRI1 expression with various tissue-specific promoters implied that local brassinosteroid signaling may instruct growth non-cell-autonomously. Here we performed such rescues with a panel of receptor variants and promoters, in combination with tissue-specific transgene knockouts. Our experiments demonstrate that brassinosteroid receptor expression in several tissues is necessary but not sufficient for rescue. Moreover, complementation with tissue-specific promoters requires the genuine BRI1 gene body sequence, which confers ubiquitous expression of trace receptor amounts that are sufficient to promote brassinosteroid-dependent root growth. Our data, therefore, argue for a largely cell-autonomous action of brassinosteroid receptors.

plant biology↗

bioRxiv2024

Sucrose-responsive osmoregulation of plant cell size by a long non-coding RNA

The shoot of green plants is the primary site of carbon assimilation into sugars, the key source of energy and metabolic building blocks. The systemic transport of sugars is essential for plant growth and morphogenesis. Plants evolved intricate networks of molecular players to effectively orchestrate the subcellular partitioning of sugars. Dynamic distribution of these osmotically active compounds is a handy tool to regulate cell turgor pressure. Pressure-induced mechanical forces play an instructive role in developmental biology across kingdoms. Here, we functionally characterized a long non-coding RNA, CARMA, as a negative regulator of a receptor-like kinase, CANAR. Sugar-responsive CARMA specifically fine-tunes CANAR expression in the phloem, the route of sugar transport. By controlling sugar distribution, the CARMA-CANAR module allows cells to flexibly adapt to the external osmolality and adjust the size of vascular cell types during organ growth and development. We identify a nexus of plant vascular tissue formation with cell internal pressure monitoring and reveal a novel functional aspect of long non-coding RNAs in developmental biology.

plant biology↗

bioRxiv2022

Heterologous expression of a lycophyte protein enhances angiosperm seedling vigor

Seedling vigor is a key agronomic trait that determines juvenile plant performance. Angiosperm seeds develop inside fruits and are connected to the mother plant through vascular tissues. Their formation requires plant-specific genes, such as BREVIS RADIX (BRX) in Arabidopsis thaliana roots. BRX family proteins are found throughout the angiosperms but also occur in non-vascular bryophytes and non-seed lycophytes. They consist of four conserved domains, including the tandem "BRX-domains". We found that bryophyte or lycophyte BRX homologs can only partially substitute for Arabidopsis BRX (AtBRX) because they miss key features in the linker between the BRX-domains. Intriguingly however, expression of a BRX homolog from the lycophyte Selaginella moellendorffii (SmBRX) in A. thaliana wildtype background confers robustly enhanced root growth vigor that persists throughout the life cycle. This effect can be traced back to a substantial increase in seed and embryo size, and can be reproduced with a modified, "SmBRX-like" variant of AtBRX. Our results thus suggest that BRX variants could serve as biotechnological tools to boost seedling vigor and shed light on the activity of ancient, non-angiosperm BRX family proteins.

plant biology↗

bioRxiv2021

Metaphloem development in the Arabidopsis root tip

The phloem transport network is a major evolutionary innovation that enabled plants to dominate terrestrial ecosystems. In the growth apices, the meristems, apical stem cells continuously produce early, so-called protophloem. This is easily observed in Arabidopsis root meristems, where the differentiation of individual protophloem sieve element precursors into interconnected, conducting sieve tubes is laid out in a spatio-temporal gradient. The mature protophloem eventually collapses as the neighboring metaphloem takes over its function further distal from the stem cell niche. Compared to protophloem, metaphloem ontogenesis is poorly characterized, primarily because its visualization is challenging. Here we describe an improved protocol to investigate metaphloem development in Arabidopsis root tips in combination with a set of new molecular markers. We found that mature metaphloem sieve elements are only observed in the late post-meristematic root although their specification is initiated as soon as protophloem sieve elements enucleate. Moreover, unlike protophloem sieve elements, metaphloem sieve elements only differentiate once they have fully elongated. Finally, our results suggest that metaphloem differentiation is not directly controlled by protophloem-derived cues but rather follows a distinct, robust developmental trajectory. Summary statementMetaphloem sieve element differentiation in Arabidopsis roots follows a robust developmental trajectory.

plant biology↗

bioRxiv2021

A conserved regulatory module regulates receptor kinase signaling in immunity and development

Ligand recognition by cell-surface receptors underlies development and immunity in both animals and plants. Modulating receptor signaling is critical for appropriate cellular responses but the mechanisms ensuring this are poorly understood. Here, we show that signaling by plant receptors for pathogen-associated molecular patterns (PAMPs) in immunity and CLAVATA3/EMBRYO SURROUNDING REGION-RELATED peptides (CLEp) in development employ a similar regulatory module. In the absence of ligand, signaling is dampened through association with specific type-2C protein phosphatases (PP2Cs). Upon activation, PAMP and CLEp receptors phosphorylate divergent cytosolic kinases, which, in turn, phosphorylate the phosphatases, thereby promoting their release from the receptor complexes. Our work reveals a regulatory circuit shared between immune and developmental receptor signaling, which may have broader important implications for plant receptor kinase-mediated signaling in general.

plant biology↗