Biology subjects

Hajny, J.

Publications and source records attributed to Hajny, J..

5 recordsLinked to original sources

bioRxiv2025

CYSTEINE-RICH RLK2 regulates development via callose synthase-dependent symplastic transport in Arabidopsis

CYSTEINE-RICH RECEPTOR-LIKE PROTEIN KINASEs (CRKs) play an important role in plant development and stress responses. One of the best described members of the Arabidopsis CRK family is CRK2, which was proposed as a crucial regulator of intercellular transport facilitated by plasmodesmata (PD). As intercellular channels allowing symplastic communication, PD-mediated transport is predominantly regulated by callose synthase (CALS)-mediated callose deposition. This process can impact not just the distribution of molecules between adjacent cells, but also the symplastic loading of vascular tissue, thereby influencing plant stress responses and developmental processes. Here we described the overlapping expression pattern of genes encoding phylogenetically closely related CALS1 and CALS3. Both CALSs were phosphorylated in vitro by CRK2, and the genetic interaction between genes encoding CRK2 and CALS1 or CALS3 revealed their impact on callose deposition, rosette growth, primary root length, and development, represented as a decreased number of true leaves. Importantly, we observed significant accumulation of starch in crk2 mutant plants, especially in developmentally older leaves, which was reverted by the independent introduction of cals1.5 and cals3.1 into the crk2 mutant background. The observed starch accumulation was accompanied by photosynthesis inhibition. We propose that the growth and developmental alterations of crk2 are caused by decreased phloem loading, which resulted in starch accumulation in source organs, and subsequent sink tissue starvation. Our results propose CRK2 as negative regulator of CALS1 and CALS3 regulating source to sink transport, which impacts plant growth and development.

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

Cell surface auxin signalling directly targets PIN-mediated auxin fluxes for adaptiveplant development

Phytohormone auxin and its directional transport mediate much of the remarkably plastic development of higher plants. Positive feedback between auxin signaling and transport is a key prerequisite for (i) self-organizing processes including vascular tissue formation and (ii) directional growth responses such as gravitropism. Here we identify a mechanism, by which auxin signaling directly targets PIN auxin transporters. Via the cell-surface ABP1-TMK1 receptor module, auxin rapidly induces phosphorylation and thus stabilization of PIN2. Following gravistimulation, initial auxin asymmetry activates autophosphorylation of the TMK1 kinase. This induces TMK1 interaction with and phosphorylation of PIN2, stabilizing PIN2 at the lower root side, thus reinforcing asymmetric auxin flow for root bending. Upstream of TMK1 in this regulation, ABP1 acts redundantly with the root-expressed ABP1-LIKE auxin receptor ABL3. Such positive feedback between cell-surface auxin signaling and PIN-mediated polar auxin transport is fundamental for robust root gravitropism and presumably also for other self-organizing developmental phenomena.

plant biology↗

bioRxiv2022

Decoy Receptor Fine-tunes Cytokinin Signaling

Hormone perception and signaling pathways play a fundamental regulatory function in cell growth, developmental, and physiological processes in both plant and animal systems. Those pathways are activated by hormone binding to the receptor to trigger cellular responses. Equally important are mechanisms that suppress activated transduction cascades to reset the system. Different mechanisms at the level of hormone biosynthesis and deactivation through degradation, conjugation, and production of repressors that attenuate transduction cascades downstream of receptors are known. In animal systems, decoy receptors have been identified as another important mechanism for fine-tuning the activity of the signaling pathways in processes like inflammatory responses, apoptosis, and blood vessel formation. Decoy receptors recognize and bind specific signaling molecules, but they cannot activate downstream signaling pathways thus providing competitive inhibition. Here we describe the first decoy receptor in plants. We show that the splicing variant of CRE1/AHK4 receptor of cytokinin, a hormone with a key role in the regulation of cell division and meristem maintenance in plants, acts as a decoy receptor to attenuate cytokinin signaling. We propose that this novel mechanism of signaling control applies in processes when modulation of CK signaling is needed.

plant biology↗

bioRxiv2021

Rapid auxin-mediated phosphorylation of Myosin regulates trafficking and polarity in Arabidopsis

The signaling molecule auxin controls plant development through a well-known transcriptional mechanism that regulates many genes. However, auxin also triggers cellular responses within seconds or minutes, and mechanisms mediating such fast responses have remained elusive. Here, we identified an ultrafast auxin-mediated protein phosphorylation response in Arabidopsis roots that is largely independent of the canonical TIR1/AFB receptors. Among targets of this novel response are Myosin XI and its adaptor protein MadB2. We show that their auxin-mediated phosphorylation regulates trafficking and polar, subcellular distribution of PIN auxin transporters. This phosphorylation-based auxin signaling module is indispensable during developmental processes that rely on auxin-mediated PIN repolarization, such as termination of shoot gravitropic bending or vasculature formation and regeneration. Hence, we identified a fast, non-canonical auxin response targeting multiple cellular processes and revealed auxin-triggered phosphorylation of a myosin complex as the mechanism for feedback regulation of directional auxin transport, a central component of auxin canalization, which underlies self-organizing plant development.

plant biology↗