Biology subjects

Klamke, M.

Publications and source records attributed to Klamke, M..

3 recordsLinked to original sources

bioRxiv2026

It takes two to tango: evolutionary divergence and functional interplay of AZG1 and AZG2 cytokinin transporters

The evolution of complex plant body architectures required the refinement of hormone transport networks, yet the evolutionary origins and functional diversification of cytokinin transporters remain unclear. Here, we reconstruct the molecular evolution of the AZA-GUANINE RESISTANT (AZG) family from bacteria and fungi to land plants. We show that AZG1 represents the ancestral land plant orthologue, preserving highly conserved proton-coupling residues present in streptophyte algae. Conversely, AZG2 emerged during vascular plant diversification and displays a distinct relaxation of evolutionary constraints within the ligand-binding pocket, providing a molecular basis for its transition to a proton-independent mechanism. Structural modeling and split-ubiquitin assays further reveal that despite this ancient sequence divergence, AZG1 and AZG2 have retained the biochemical capacity to physically heterodimerize. Together, our findings uncover the stepwise evolutionary innovation of the AZG family and link structural diversification to the increasing complexity of plant hormone transport networks.

plant biology↗

bioRxiv2026

Boosting NADP-malic enzyme 1 enhances seed vigor and longevity in Arabidopsis thaliana

Seed longevity is a key determinant of crop establishment, productivity, and germplasm conservation. During storage and germination, reactive oxygen species accumulate and contribute to seed aging through oxidative damage and loss of viability. The maintenance of redox homeostasis therefore relies on NADPH-dependent antioxidant systems, which require a continuous supply of reducing power. NADP-dependent malic enzyme 1 (NADP-ME1), represents a source of NADPH supporting antioxidant defense during seed aging. Here, we show that enhanced expression of NADP-ME1 positively contributes to seed vigor and longevity in Arabidopsis thaliana. NADP-ME1 overexpression lines exhibited faster germination and higher overall germination after accelerated aging, whereas knockout mutants showed markedly reduced germination performance. Enhanced post-aging vigor in the overexpression lines was associated with reduced oxidative damage as indicated by lower malondialdehyde and hydrogen peroxide accumulation, along with preservation of specific polyunsaturated fatty acids, and increased {gamma}-tocopherol levels in aged dry seeds. Enhanced expression of NADP-ME1 reshapes the transcriptome of germinated seeds under fresh conditions compared with the wild type, while only minimal differences between genotypes are detected in aged seeds. These results suggest that NADP-ME1 contributes to the establishment of a transcriptional state associated with enhanced seed vigor and improved post-aging germination. Finally, co-immunoprecipitation coupled to mass spectrometry and bimolecular fluorescence complementation identified aspartate aminotransferase 2 as a NADP-ME1 interactor, pointing to a link between malate metabolism and amino acid-related metabolic adjustment. Together, these results identify NADP-ME1 as a determinant of seed resilience to aging and a potential target for improving seed quality.

plant biology↗

bioRxiv2026

NADP-malic enzyme 1 couples ABA signaling to ROS-auxin patterning to restrict Arabidopsis root growth

Abscisic acid (ABA) restricts primary root growth by reshaping reactive oxygen species (ROS) dynamics and hormone signaling at the root apex, yet how cellular reductant supply for redox homeostasis is integrated into this response remains unclear. Here, we show that the cytosolic NADP-dependent malic enzyme 1 (NADP-ME1) is required for full ABA inhibition of Arabidopsis primary root elongation after germination. Three independent me1 loss-of-function mutants retained significant elongation of primary roots under ABA compared with wild type. In wild type, ABA induced an asymmetric auxin response at the root tip, whereas me1 roots failed to establish this auxin asymmetry and instead accumulated superoxide, indicating disrupted ROS balance. Pharmacological perturbation of auxin transport and ethylene biosynthesis/signaling attenuated the mutant phenotype, linking NADP-ME1 function to auxin-ethylene interactions during ABA-regulated growth. NADP-ME1 loss amplifies ABA-dependent transcriptional rewiring, including induction of oxidative stress and depression of growth-associated hormone modules. Co-immunoprecipitation coupled with bimolecular fluorescence complementation identified ascorbate peroxidase 1 (APX1) and major latex protein-like 34 (MLP34) as NADP-ME1 interaction partners, suggesting functional coupling between NADPH production and ROS detoxification. Together, our results support a model in which NADP-ME1 shapes the superoxide/H2O2 balance to control auxin patterning at the root tip and thereby execute ABA-mediated growth inhibition.

plant biology↗