Biology subjects

Tessi, T. M.

Publications and source records attributed to Tessi, T. 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↗

bioRxiv2020

The auxin transporter PIN1 and the cytokinin transporter AZG1 interact to regulate the root stress response

Root system development is crucial for optimal growth and yield in plants, especially in sub-optimal soil conditions. The architecture of a root system is environmentally responsive, enabling the plant to exploit regions of high nutrient density whilst simultaneously minimizing abiotic stress. Despite the vital contribution of root systems to the growth of both model and crop species, we know little of the mechanisms which regulate their architecture. One factor which is relatively well understood is the transport of auxin, a plant growth regulator which defines the frequency of lateral root (LR) initiation and the rate of LR outgrowth. Here we describe a search for proteins which regulate RSA by interacting directly with a key auxin transporter, PIN1. The native separation of PIN1 identified several co-purifying proteins. Among them, AZG1 was subsequently confirmed as a PIN1 interactor. AZG1-GFP fusions co-localized with PIN1 in procambium cells of the root meristem. Roots of azg1 plants contained less PIN1 and blocking proteolysis restored PIN1 levels, observations which are consistent with PIN1 being stabilized by AZG1 in the plasma membrane. Furthermore, we show that AZG1 is a cytokinin import protein; accordingly, azg1 plants are insensitive to exogenously applied cytokinin. In wild-type plants, the frequency of LRs falls with increasing salt concentration, a response which is not observed in azg1 x azg2 plants, although their drought response is unimpaired. This report therefore identifies a potential point for auxin:cytokinin crosstalk in the environmentally-responsive determination of root system architecture.

plant biology↗

bioRxiv2020

Arabidopsis AZG2, an auxin induced putative cytokinin transporter, regulates lateral root emergence

The phytohormones cytokinin (CK) and auxin are key regulators of plant growth and development. During the last decade specialised transport mechanisms turned out to be the key for the control of local and long distance hormone distributions. In contrast to auxin, CK transport is poorly understood. Here we show that Arabidopsis thaliana AZG2, a member of the AZG purine transporter family, acts as CK transporter involved in the determination of the root system architecture. The expression of AtAZG2 is primarily auxin dependent and restricted to a small group of cells surrounding the lateral root primordia. Compared to wild type, mutants carrying loss-of-function alleles of Atazg2 have higher density of lateral roots, suggesting AZG2 as being part of a regulatory pathway in lateral root emergence. Moreover, azg2 mutants are partially insensitive to exogenously applied CK, which is consistent with the observation that the CK reporter gene TCSnpro:GFP showed lower fluorescence signal in the roots of azg2 mutants compared to those of wild type. These results indicate a defective CK signalling pathway in the region of lateral root primordia. By the integration of AtAZG2 subcellular localization and CK transport capacity data, our results allowed us to propose a local Auxin/CK signalling model for the regulation of lateral root emergence.

plant biology↗