Highlight textTranscriptional repression of STP1 is rapidly induced by phosphorylatable sugars through an HXK1-independent signalling pathway involving the participation of sugar-responsive cis elements localized in the promoter.

In recent years, the transcription factor ABI4 has emerged as an important node of integration for external and internal signals such as nutrient status and hormone signaling that modulates critical transitions during the growth and development of plants. For this reason, understanding the mechanism of action and regulation of this protein represents an important step towards the elucidation of crosstalk mechanisms in plants. However, this understanding has been hindered due to the negligible levels of this protein as a result of multiple posttranscriptional regulations. To better understand the function and regulation of the ABI4 protein in this work, we performed a functional analysis of several evolutionarily conserved motifs. Based on these conserved motifs, we identified ortholog genes of ABI4 in different plant species. The functionality of the putative ortholog from Theobroma cacao was demonstrated in transient expression assays and in complementation studies in plants. The function of the highly conserved motifs was analyzed after their deletion or mutagenesis in the Arabidopsis ABI4 sequence using mesophyll protoplasts. This approach permitted us to immunologically detect the ABI4 protein and identify some of the mechanisms involved in its regulation. We identified sequences required for the nuclear localization (AP2-associated motif) as well as those for transcriptional activation function (LRP motif). Moreover, this approach showed that the protein stability of this transcription factor is controlled through protein degradation and subcellular localization and involves the AP2-associated and the PEST motifs. We demonstrated that the degradation of ABI4 protein through the PEST motif is mediated by the 26S proteasome in response to changes in the sugar levels.

La conversión de la energía solar a energía química en las plantas se realiza a través de la fotosíntesis, que es el principal sostén para la vida en el planeta, ya que es en este proceso en el que se da la fijación del CO2 y como resultado final los azúcares, que son la fuente principal de energía para los tejidos no fotosintéticos de las plantas. Durante la evolución, los azúcares no solo fueron, sino son una fuente de energía para las plantas y adquirieron la función de moléculas señalizadoras; es decir, moléculas mensajeras que perciben y comunican las variaciones del estado energético de la planta a través de diversos receptores proteícos situados extracelular e intracelularmente. Tanto los monosacáridos (glucosa y fructosa) como los disacáridos (sacarosa y trehalosa) desencadenan diferentes vías de señalización que involucran la participación de diversas cinasas y factores de transcripción para modular la expresión de diversos genes relacionados con el crecimiento, desarrollo y respuesta al estrés de las plantas. El objetivo de esta revisión es proporcionar un panorama general de las fuentes que generan los azúcares, sus mecanismos de transporte, así como el conocimiento actual de la percepción y la señalización mediada por estos compuestos y su impacto en la vida de las plantas.

The ABA-INSENSITIVE 4 transcription factor is key for the regulation of diverse aspects of plant development and environmental responses, including proper perception of hormonal and nutritional signals. ABI4 activity is highly regulated at the transcriptional and post-transcriptional levels leading to precise expression mainly in the developing seed and early seedling development. Based on genetic and molecular approaches in the current study we provide new insights into the central mechanism underpinning the transcriptional regulation of ABI4 during both seed and vegetative development. We identified a complex interplay between the LEC2 and ABI3 transcriptional activators and the HSI/VAL repressors that is critical for proper ABI4 expression. Interestingly, the regulation by these proteins relies on the two RY cis-acting motifs present two kb upstream of the ABI4 gene. Our analysis also shows that the chromatin landscape of the ABI4 loci is highly dependent on the LEC2 and HSI2/VAL proteins. LEC2 regulation extends to the vegetative development and the absence of this factor results in ABA- and sugar-insensitive signaling in the developing plant. This regulatory circuit functions as a major control module for the correct spatial-temporal expression of ABI4 and prevents its ectopic accumulation that is harmful to the plant.