ATL Protein Family: Novel Regulators in Plant Response to Environmental Stresses.

Plants actively develop intricate regulatory mechanisms to counteract the harmful effects of environmental stresses. The ubiquitin-proteasome pathway, a crucial mechanism, employs E3 ligases (E3s) to facilitate the conjugation of ubiquitin to specific target substrates, effectively marking them for proteolytic degradation. E3s play critical roles in many biological processes, including phytohormonal signaling and adaptation to environmental stresses. Arabidopsis Toxicosa en Levadura (ATL) proteins, belonging to a subfamily of RING-H2 E3s, actively modulate diverse physiological processes and plant responses to environmental stresses. Despite studies on the functions of certain ATL family members in rice and Arabidopsis, most ATLs still need more comprehensive study. This review presents an overview of the ubiquitin-proteasome system (UPS), specifically focusing on the pivotal role of E3s and associated enzymes in plant development and environmental adaptation. Our study seeks to unveil the active modulation of plant responses to environmental stresses by E3s and ATLs, emphasizing the significance of ATLs within this intricate process. By emphasizing the importance of studying the roles of E3s and ATLs, our review contributes to developing more resilient plant varieties and promoting sustainable agricultural practices while establishing a research roadmap for the future.

OsATL38 mediates mono-ubiquitination of the 14-3-3 protein OsGF14d and negatively regulates the cold stress response in rice.

One of the major regulatory pathways that permits plants to convert an external stimulus into an internal cellular response within a short period of time is the ubiquitination pathway. In this study, OsATL38 was identified as a low temperature-induced gene that encodes a rice homolog of Arabidopsis Tóxicos en Levadura RING-type E3 ubiquitin (Ub) ligase, which was predominantly localized to the plasma membrane. OsATL38-overexpressing transgenic rice plants exhibited decreased tolerance to cold stress as compared with wild-type rice plants. In contrast, RNAi-mediated OsATL38 knockdown transgenic progeny exhibited markedly increased tolerance to cold stress relative to that of wild-type plants, which indicated a negative role of OsATL38 in response to cold stress. Yeast two-hybrid, in vitro pull-down, and co-immunoprecipitation assays revealed that OsATL38 physically interacted with OsGF14d, a rice 14-3-3 protein. An in vivo target ubiquitination assay indicated that OsGF14d was mono-ubiquitinated by OsATL38. osgf14d knockout mutant plants were more sensitive to cold stress than wild-type rice plants, indicating that OsGF14d is a positive factor in the response to cold stress. These results provide evidence that the RING E3 Ub ligase OsATL38 negatively regulates the cold stress response in rice via mono-ubiquitination of OsGF14d 14-3-3 protein.

Arabidopsis Tóxicos en Levadura 78 (AtATL78) mediates ABA-dependent ROS signaling in response to drought stress.

Plants have developed a variety of complicated responses to cope with drought, one of the most challenging environmental stresses. As a quick response, plants rapidly inhibit stomatal opening under the control of abscisic acid (ABA) signaling pathway, in order to preserve water. Here, we report that Arabidopsis Tóxicos en Levadura (ATL), a RING-type E3 ubiquitin ligase, mediates the ABA-dependent stomatal closure. In contrast to wild-type plants, the stomatal closure was fully impaired in atatl78 mutant plants even in the presence of exogenous ABA and reactive oxygen species (ROS). Besides, under high concentrations of Ca(2+), a down-stream signaling molecule of ABA signaling pathway, atatl78 mutant plants successfully closed the pores. Furthermore, AtATL78 protein indirectly associated with catalases and the deficiency of AtATL78 led the reduction of catalase activity and H2O2, implying the function of AtATL78 in the modulation of ROS activity. Based on these results, we suggest that AtATL78 possibly plays a role in promoting ROS-mediated ABA signaling pathway during drought stress.