Nitric oxide-mediated S-nitrosylation of IAA17 protein in intrinsically disordered region represses auxin signaling

The interplay between extracellular and intracellular auxin signaling in plants

The phytohormone auxin exerts control over remarkable developmental processes in plants. It moves from cell to cell, resulting in the creation of both extracellular auxin and intracellular auxin, which are recognized by distinct auxin receptors. These two auxin signaling systems govern different auxin responses while working together to regulate plant development. In this review, we outline the latest research advancements in unraveling these auxin signaling pathways, encompassing auxin perception and signaling transductions. We emphasize the interaction between extracellular and intracellular auxin, which contributes to the intricate role of auxin in plant development.

Phosphorylation of auxin signaling repressor IAA8 by heat-responsive MPKs causes defective flower development

Heat stress is a substantial and imminent threat to plant growth and development. Understanding its adverse effects on plant development at the molecular level is crucial for sustainable agriculture. However, the molecular mechanism underlying how heat stress causes developmental defects in flowers remains poorly understood. Here, we identified Indole-3-Acetic Acid 8 (IAA8), a repressor of auxin signaling, as a substrate of mitogen-activated protein kinases (MPKs) in Arabidopsis thaliana, and found that MPK-mediated phosphorylation of IAA8 inhibits flower development. MPKs phosphorylated three residues of IAA8: S74, T77, and S135. Interestingly, transgenic plants overexpressing a phospho-mimicking mutant of IAA8 (IAA8DDD OX) exhibited defective flower development due to high IAA8 levels. Furthermore, MPK-mediated phosphorylation inhibited IAA8 polyubiquitination, thereby significantly increasing its stability. Additionally, the expression of key transcription factors involved in flower development, such as bZIP and MYB genes, was significantly perturbed in the IAA8DDD OX plants. Collectively, our study demonstrates that heat stress inhibits flower development by perturbing the expression of flower development genes through the MPK-mediated phosphorylation of IAA8, suggesting that Aux/IAA phosphorylation enables plants to fine-tune their development in response to environmental stress.

Metabolism of 2,4-D in plants: comparative analysis of metabolic detoxification pathways in tolerant crops and resistant weeds

The commercialization of 2,4-D (2,4-dichlorophenoxyacetic acid) latifolicide in 1945 marked the beginning of the selective herbicide market, with this active ingredient playing a pivotal role among commercial herbicides due to the natural tolerance of monocots compared with dicots. Due to its intricate mode of action, involving interactions within endogenous auxin signaling networks, 2,4-D was initially considered a low-risk herbicide to evolve weed resistance. However, the intensification of 2,4-D use has contributed to the emergence of 2,4-D-resistant broadleaf weeds, challenging earlier beliefs. This review explores 2,4-D tolerance in crops and evolved resistance in weeds, emphasizing an in-depth understanding of 2,4-D metabolic detoxification. Nine confirmed 2,4-D-resistant weed species, driven by rapid metabolism, highlight cytochrome P450 monooxygenases in Phase I and glycosyltransferases in Phase II as key enzymes. Resistance to 2,4-D may also involve impaired translocation associated with mutations in auxin/indole-3-acetic acid (Aux/IAA) co-receptor genes. Moreover, temperature variations affect 2,4-D efficacy, with high temperatures increasing herbicide metabolism rates and reducing weed control, while drought stress did not affect 2,4-D efficacy. Research on 2,4-D resistance has primarily focused on non-target-site resistance (NTSR) mechanisms, including 2,4-D metabolic detoxification, with limited exploration of the inheritance and genetic basis underlying these traits. Resistance to 2,4-D in weeds is typically governed by a single gene, either dominant or incompletely dominant, raising questions about gain-of-function or loss-of-function mutations that confer resistance. Future research should unravel the physiological and molecular-genetic basis of 2,4-D NTSR, exploring potential cross-resistance patterns and assessing fitness costs that may affect future evolution of auxin-resistant weeds. © 2024 Society of Chemical Industry.

AuxSynBio: synthetic biology tools to understand and engineer auxin

The plant hormone auxin is a crucial coordinator of nearly all plant growth and development processes. Because of its centrality to plant physiology and the modular nature of the signaling pathway, auxin has played a critical role at the forefront of plant synthetic biology. This review will highlight how auxin is both a subject and an object of synthetic biology. Engineering biology approaches are deepening our understanding of how auxin pathways are wired and tuned, particularly through the creative use of signaling pathway recapitulation in yeast and engineered orthogonal auxin-receptor pairs. Auxin biology has also been mined for parts by synthetic biologists, with components being used for inducible protein degradation systems (auxin-inducible degron), auxin biosensors, synthetic cell-cell communication, and plant engineering.

Role of protein S-nitrosylation in plant growth and development

In plants, nitric oxide (NO) has been widely accepted as a signaling molecule that plays a role in different processes. Among the most relevant pathways by which NO and its derivatives realize their biological functions, post-translational protein modifications are worth mentioning. Protein S-nitrosylation has been the most studied NO-dependent regulatory mechanism; it is emerging as an essential mechanism for transducing NO bioactivity in plants and animals. In recent years, the research of protein S-nitrosylation in plant growth and development has made significant progress, including processes such as seed germination, root development, photosynthetic regulation, flowering regulation, apoptosis, and plant senescence. In this review, we focus on the current state of knowledge on the role of S-nitrosylation in plant growth and development and provide a better understanding of its action mechanisms.

SERK3A and SERK3B could be S-nitrosylated and enhance the salt resistance in tomato seedlings

Salinity hinders plant growth and development, resulting in reduced crop yields and diminished crop quality. Nitric oxide (NO) and brassinolides (BR) are plant growth regulators that coordinate a plethora of plant physiological responses. Nonetheless, the way in which these factors interact to affect salt tolerance is not well understood. BR is perceived by the BR receptor BRASSINOSTEROID INSENSITIVE 1 (BRI1) and its co-receptor BRI1-associated kinase 1 (BAK1) to form the receptor complex, eventually inducing BR-regulated responses. To response stress, a wide range of NO-mediated protein modifications is undergone in eukaryotic cells. Here, we showed that BR participated in NO-enhanced salt tolerance of tomato seedlings (Solanum lycopersicum cv. Micro-Tom) and NO may activate BR signaling under salt stress, which was related to NO-mediated S-nitrosylation. Further, in vitro and in vivo results suggested that BAK1 (SERK3A and SERK3B) was S-nitrosylated, which was inhibited under salt condition and enhanced by NO. Accordingly, knockdown of SERK3A and SERK3B reduced the S-nitrosylation of BAK1 and resulted in a compromised BR response, thereby abolishing NO-induced salt tolerance. Besides, we provided evidence for the interaction between BRI1 and SERK3A/SERK3B. Meanwhile, NO enhanced BRI1-SERK3A/SERK3B interaction. These results imply that NO-mediated S-nitrosylation of BAK1 enhances the interaction BRI1-BAK1, facilitating BR response and subsequently improving salt tolerance in tomato. Our findings illustrate a mechanism by which redox signaling and BR signaling coordinate plant growth in response to abiotic stress.

FERONIA-mediated TIR1/AFB2 oxidation stimulates auxin signaling in Arabidopsis

The phytohormone auxin plays a pivotal role in governing plant growth and development. Although the TRANSPORT INHIBITOR RESPONSE1/AUXIN SIGNALING F-BOX (TIR1/AFB) receptors function in both the nucleus and cytoplasm, the mechanism governing the distribution of TIR1/AFBs between these cellular compartments remains unknown. In this study, we demonstrate that auxin-mediated oxidation of TIR1/AFB2 is essential for their targeting to the nucleus. We showed that small active molecules, reactive oxygen species (ROS) and nitric oxide (NO), are indispensable for the nucleo-cytoplasmic distribution of TIR1/AFB2 in trichoblasts and root hairs. Further studies revealed that this process is regulated by the FERONIA receptor kinase-NADPH oxidase signaling pathway. Interestingly, ROS and NO initiate oxidative modifications in TIR1C140/516 and AFB2C135/511, facilitating their subsequent nuclear import. The oxidized forms of TIR1C140/516 and AFB2C135/511 play a crucial role in enhancing the function of TIR1 and AFB2 in transcriptional auxin responses. Collectively, our study reveals a novel mechanism by which auxin stimulates the transport of TIR1/AFB2 from the cytoplasm to the nucleus, orchestrated by the FERONIA-ROS signaling pathway.

Protein post-translational modifications in auxin signaling

Protein post-translational modifications (PTMs), such as ubiquitination, phosphorylation, and small ubiquitin-like modifier (SUMO)ylation, are crucial for regulating protein stability, activity, subcellular localization, and binding with cofactors. Such modifications remarkably increase the variety and complexity of proteomes, which are essential for regulating numerous cellular and physiological processes. The regulation of auxin signaling is finely tuned in time and space to guide various plant growth and development. Accumulating evidence indicates that PTMs play critical roles in auxin signaling regulations. Thus, a thorough and systematic review of the functions of PTMs in auxin signal transduction will improve our profound comprehension of the regulation mechanism of auxin signaling and auxin-mediated various processes. This review discusses the progress of protein ubiquitination, phosphorylation, histone acetylation and methylation, SUMOylation, and S-nitrosylation in the regulation of auxin signaling.

Auxin and abiotic stress responses

Plants are exposed to a variety of abiotic stresses; these stresses have profound effects on plant growth, survival, and productivity. Tolerance and adaptation to stress require sophisticated stress sensing, signaling, and various regulatory mechanisms. The plant hormone auxin is a key regulator of plant growth and development, playing pivotal roles in the integration of abiotic stress signals and control of downstream stress responses. In this review, we summarize and discuss recent advances in understanding the intersection of auxin and abiotic stress in plants, with a focus on temperature, salt, and drought stresses. We also explore the roles of auxin in stress tolerance and opportunities arising for agricultural applications.

SOURSOP: A Python Package for the Analysis of Simulations of Intrinsically Disordered Proteins

Conformational heterogeneity is a defining hallmark of intrinsically disordered proteins and protein regions (IDRs). The functions of IDRs and the emergent cellular phenotypes they control are associated with sequence-specific conformational ensembles. Simulations of conformational ensembles that are based on atomistic and coarse-grained models are routinely used to uncover the sequence-specific interactions that may contribute to IDR functions. These simulations are performed either independently or in conjunction with data from experiments. Functionally relevant features of IDRs can span a range of length scales. Extracting these features requires analysis routines that quantify a range of properties. Here, we describe a new analysis suite simulation analysis of unfolded regions of proteins (SOURSOP), an object-oriented and open-source toolkit designed for the analysis of simulated conformational ensembles of IDRs. SOURSOP implements several analysis routines motivated by principles in polymer physics, offering a unique collection of simple-to-use functions to characterize IDR ensembles. As an extendable framework, SOURSOP supports the development and implementation of new analysis routines that can be easily packaged and shared.