Plants must effectively respond to various environmental stimuli to achieve optimal growth. This is especially relevant in the context of climate change, where drought emerges as a major factor globally impacting crops and limiting overall yield potential. Throughout evolution, plants have developed adaptative strategies for environmental stimuli, with plant hormones and reactive oxygen species (ROS) playing essential roles in their development. Hormonal signaling and the maintenance of ROS homeostasis are interconnected, playing indispensable roles in growth, development, and stress responses and orchestrating diverse molecular responses during environmental adversities. Nine principal classes of phytohormones have been categorized: auxins, brassinosteroids, cytokinins, and gibberellins primarily oversee developmental growth regulation, while abscisic acid, ethylene, jasmonic acid, salicylic acid, and strigolactones are the main orchestrators of environmental stress responses. Coordination between phytohormones and transcriptional regulation is crucial for effective plant responses, especially in drought stress. Understanding the interplay of ROS and phytohormones is pivotal for elucidating the molecular mechanisms involved in plant stress responses. This review provides an overview of the intricate relationship between ROS, redox metabolism, and the nine different phytohormones signaling in plants, shedding light on potential strategies for enhancing drought tolerance for sustainable crop production.

Ascorbate peroxidases (APXs) are heme peroxidases involved in the control of hydrogen peroxide levels and signal transduction pathways related to development and stress responses. Here, a total of 238 APX, 30 APX-related (APX-R), and 34 APX-like (APX-L) genes were identified from 24 species from the Poaceae family. Phylogenetic analysis of APX indicated five distinct clades, equivalent to cytosolic (cAPX), peroxisomal (pAPX), mitochondrial (mitAPX), stromal (sAPX), and thylakoidal (tAPX) isoforms. Duplication events contributed to the expansion of this family and the divergence times. Different from other APX isoforms, the emergence of Poaceae mitAPXs occurred independently after eudicot and monocot divergence. Our results showed that the constitutive silencing of mitAPX genes is not viable in rice plants, suggesting that these isoforms are essential for rice regeneration or development. We also obtained rice plants silenced individually to sAPX isoforms, demonstrating that, different to plants double silenced to both sAPX and tAPX or single silenced to tAPX previously obtained, these plants do not show changes in the total APX activity and hydrogen peroxide content in the shoot. Among rice plants silenced to different isoforms, plants silenced to cAPX showed a higher decrease in total APX activity and an increase in hydrogen peroxide levels. These results suggest that the cAPXs are the main isoforms responsible for regulating hydrogen peroxide levels in the cell, whereas in the chloroplast, this role is provided mainly by the tAPX isoform. In addition to broadening our understanding of the core components of the antioxidant defense in Poaceae species, the present study also provides a platform for their functional characterization.

Castor bean (Ricinus communis L.) can tolerate long periods of dehydration, allowing the investigation of gene circuits involved in drought tolerance. Genes from gibberellins, jasmonates, and auxin signaling are important for crosstalk in the developmental and environmental adaptation process to drought conditions. However, the genes related to these signals, as well as their transcription profiles under drought, remain poorly characterized in the castor bean. In the present work, genes from gibberellins, jasmonates, and auxin signaling were identified and molecularly characterized. These analyses allowed us to identify genes encoding receptors, inhibitory proteins, and transcription factors from each signaling pathway in the castor bean genome. Chromosomal distribution, gene structure, evolutionary relationships, and conserved motif analyses were performed. Expression analysis through RNA-seq and RT-qPCR revealed that gibberellins, jasmonates, and auxin signaling were modulated at multiple levels under drought, with notable changes in specific genes. The gibberellin receptor RcGID1c was downregulated in response to drought, and RcDELLA3 was strongly repressed, whereas its homologues were not, reinforcing the suggestion of a nuanced regulation of gibberellin signaling during drought. Considering jasmonate signaling, the downregulation of the transcription factor RcMYC2 aligned with the drought tolerance observed in mutants lacking this gene. Altogether, these analyses have provided insights into hormone signaling in the castor bean, unveiling transcriptional responses that enhance our understanding of high drought tolerance in this plant. This knowledge opens avenues for identifying potential candidate genes suitable for genetic manipulation in biotechnological approaches.

Small RNAs (sRNAs) are widespread across diverse flowering plant species and play important roles regulating reproduction and environmental responses. However, how sRNAs exert their function is largely unknown, likely due to their typical origin in non-genic regions, the lack of distinct gene targets, and the sparse characterization of their associated Argonaute (AGO) effector proteins. Here we show that Arabidopsis male reproductive sRNAs associate with AGO4, 5, 6 and 9, all of which are enriched in meiocytes along with RNA Polymerase V (Pol V). This enables these sRNAs to methylate loci with imperfect sequence homology. AGO4, AGO6 and AGO9 predominantly load 24-nucleotide (nt) Pol IV-derived sRNAs and mediate DNA methylation in meiocytes in a dosage-dependent manner. Despite closer homology to microRNA-associated AGO1 and AGO10, AGO5 primarily binds CLSY3- and Pol IV-derived 21-24 nt sRNAs. Transcriptomic and methylomic analyses of meiocytes from single and compound ago mutants demonstrate distinct yet complementary roles of AGO4/6/9 and AGO5 in regulating protein-coding genes and silencing transposons in the germline. These molecular disruptions are accompanied by significant meiotic defects. Together, our findings reveal how AGO4/6/9-mediated DNA methylation and AGO5, likely acting through post-transcriptional gene silencing, work together to promote male germline development.

Nucleoside diphosphate kinase (NDPK) is a ubiquitous enzyme that maintains cellular nucleotide balance by catalyzing the transfer of phosphate groups between nucleoside diphosphates and triphosphates. Although the evolutionary conservation of NDPK is well established, several aspects of its diversification and functional adaptation remain unclear. The central question of this work is how NDPK evolved across plant species, focusing on the Solanaceae family and how its evolutionary history relates to the diversification of its cellular functions. Phylogenetic and molecular dating analyses showed that the division between NDPK groups 1 and 2 predates the divergence of plants and animals, whereas plant-specific NDPK types (I–IV) originated early in streptophyte evolution. Solanaceae species retain a conserved set of NDPK genes, including a type III isoform with features consistent with mitochondrial targeting. Functional assays in isolated potato tuber mitochondria revealed high NDPK activity in the intermembrane space, sustaining ADP supply to oxidative phosphorylation. Activation of mitochondrial NDPK induced a phosphorylative respiratory state, which partially dissipated the mitochondrial membrane potential and significantly reduced reactive oxygen species (ROS) production. GDP and UDP were preferentially phosphorylated, conferring a stronger antioxidant effect than other nucleotides. Consistently, the mitochondrial isoform StNDPK3 was upregulated during tuber development. Together, our results demonstrate that NDPKs are evolutionarily conserved yet functionally diversified enzymes in plants and identify mitochondrial NDPK as a key modulator of mitochondrial redox homeostasis. By linking nucleotide metabolism to Δψ_m control and ROS suppression, this study highlights a previously underappreciated antioxidant mechanism that integrates mitochondrial energy metabolism with developmental and stress-related processes in plants.

Hexokinases (HXKs) are key enzymes in glucose metabolism and play essential roles in energy homeostasis. In vertebrates, the HXK family has undergone extensive expansion and diversification, giving rise to multiple paralogs with distinct structural and regulatory features. Here, we present a comprehensive evolutionary analysis of the HXK gene family across Metazoa, integrating phylogenetic reconstruction, molecular dating, synteny analysis, structural comparisons, and selection pressure inference. Our results indicate that the 100 kDa hexokinase paralogs originated from domain duplication and fusion events in early vertebrates, followed by lineage-specific duplications giving rise to HXK1, HXK2, HXK3, HXK4, and HXK5. Structural analysis revealed that only HXK2 retains catalytic activity in both N- and C-terminal domains, while the other paralogs exhibit divergence and loss of N-terminal catalytic function. Selection analyses across 470 mammalian genomes revealed paralog- and lineage-specific signatures of episodic positive selection, particularly in HXK3, suggesting adaptive evolution in response to distinct metabolic demands. These findings provide new insights into the functional evolution and specialization of HXKs in vertebrate metabolism and highlight the interplay between gene duplication, structural adaptation, and selective pressures in shaping metabolic diversity.