Konstantinos E. Vlachonasios

GENERAL CONTROL NON-DEREPRESSIBLE 5 (GCN5) is a histone acetyltransferase that plays a central role in regulating plant development and responses to environmental stimuli. In root development, GCN5 promotes the maintenance of the stem cell niche and proliferation of transit-amplifying cells. SPATULA (SPT) is a basic helix-loop-helix (bHLH) transcription factor with established roles in gynoecium and carpel development, as well as broader functions in plant growth. In roots, SPT negatively regulates quiescent center size, root meristem size, and overall root growth, without substantially affecting root patterning or cell-type differentiation. To investigate a potential genetic interaction between SPT and GCN5 in root meristem development, we generated and characterized spt;gcn5 double mutants. Notably, loss of SPT partially suppressed some of the developmental defects associated with gcn5, including abnormalities in root meristem size, meristem organization, and root growth. These data suggest that a complicated genetic interaction between SPT and GCN5 regulates important aspects of root meristem growth and organization.

GENERAL CONTROL NON-DEREPRESSIBLE 5 (GCN5) is a histone acetyltransferase that plays a central role in regulating plant development and responses to environmental stimuli. In root development, GCN5 promotes the maintenance of the stem cell niche and proliferation of transit-amplifying cells. SPATULA (SPT) is a basic helix-loop-helix (bHLH) transcription factor with established roles in gynoecium and carpel development, as well as broader functions in plant growth. In roots, SPT negatively regulates quiescent center size, root meristem size, and overall root growth, without substantially affecting root patterning or cell-type differentiation. To investigate a potential genetic interaction between SPT and GCN5 in root meristem development, we generated and characterized spt;gcn5 double mutants. Notably, loss of SPT substantially suppressed some developmental defects associated with gcn5 mutations, including abnormalities in root meristem size, meristem organization, and root growth. These data suggest that a complex genetic interaction between SPT and GCN5 regulates important aspects of root meristem growth and organization.

Sterol biosynthesis underlies significant physiological functions in plants, including the production of membrane structural sterols and hormones such as brassinosteroids and cytokinins. Inhibition of sterol biosynthesis has been shown to disrupt multiple aspects of Arabidopsis thaliana development. Here, the effects of lovastatin, an inhibitor of HMG-CoA reductase, on root development were investigated, focusing on auxin–cytokinin distribution and transport. Lovastatin inhibited primary root growth, especially cell elongation, in a dose-dependent manner. Additionally, lateral root density was considerably increased and lateral root primordia (LRP) emerged ectopically. In accordance to the above defects, auxin/cytokinin imbalance was recorded by the ectopic presence of the synthetic auxin marker DR5 and a significant decrease of cytokinins, as revealed by depletion of the TCS (two-component signaling) marker. Because auxin distribution appeared disturbed, auxin transport impairment was further examined. Plasma membrane localization of PIN auxin efflux carriers declined significantly, showing additional diffuse cytoplasmic localization in LRP cells. However, the cell-specific localization patterns of several PINs and their abundance at the transcript and protein level appeared unaffected or slightly increased. Fluorescence recovery after photobleaching (FRAP) analysis regarding membrane kinetics of PIN2 revealed altered PIN2 membrane dynamics and transmission electron microscopy (TEM) observations showed structural defects at the plasma membrane-cell wall interface. Together, these results support that sterol biosynthesis is essential for maintaining plasma membrane organization, which, in turn, is key factor for the distribution of hormones that control root development. Highlights: Lovastatin treatment inhibits root growth and causes deregulated formation of lateral roots. Consistently, lovastatin causes altered patterns of auxin distribution relevant to PIN protein mis-localization and decreases cytokinin levels. These changes could be attributed to reduced structural sterols as exemplified from alteration in PIN2 membrane dynamics.

The following Special Issue highlights the sophisticated transcriptional regulatory networks governing plant development, with a specific focus on how genetic, epigenetic, and metabolic pathways integrate environmental signals to shape agronomic traits

Background/Objectives The plants of the Lavandula genus are widely investigated because of their significance for pharmaceuticals and food. The composition of lavender essential oil is determined by genotype and can be induced by environmental, ontogenetic factors, and morphogenetic features. Linalool and linalyl acetate are the most abundant compounds, performing essential ecological functions and participating in lavender’s therapeutic properties. This review reports on the biosynthesis of lavender oil compounds and summarises the environmental, developmental, and molecular factors contributing to essential oil composition in lavender flowers. Results Floral developmental stage and ontogeny are fundamental for optimal harvest time. The harvesting period for high-quality lavender essential oil is affected by environmental and developmental factors that influence the gene expression of monoterpene biosynthesis. Conclusions These findings indicate the appropriate features for high-quality lavender essential oil and contribute to information that may allow for the manipulation of monoterpenes biosynthesis in lavender breeding efforts.

Roots are usually underground plant organs, responsible for anchoring to the soil, absorbing water and nutrients, and interacting with the rhizosphere. During root development, roots respond to a variety of environmental signals, contributing to plant survival. Histone post-translational modifications play essential roles in gene expression regulation, contributing to plant responses to environmental cues. Histone acetylation is one of the most studied post-translational modifications, regulating numerous genes involved in various biological processes, including development and stress responses. Although the effect of histone acetylation on plant responses to biotic and abiotic stimuli has been extensively reviewed, no recent reviews exist focusing on root development regulation by histone acetylation. Therefore, this review brings together all the knowledge about the impact of histone acetylation on root development in several plant species, mainly focusing on Arabidopsis thaliana. Here, we summarize the role of histone acetylation and deacetylation in numerous aspects of root development, such as stem cell niche maintenance, cell division, expansion and differentiation, and developmental zone determination. We also emphasize the gaps in current knowledge and propose new perspectives for research toward deeply understanding the role of histone acetylation in root development.

Histone acetyltransferases (HATs) modify the amino-terminal tails of the core histone proteins via acetylation, regulating chromatin structure and transcription. GENERAL CONTROL NON-DEREPRESSIBLE 5 (GCN5) is a HAT that specifically acetylates H3K14 residues. GCN5 has been associated with cell division and differentiation, meristem function, root, stem, foliar, and floral development, and plant environmental response. The flowers of gcn5 plants display a reduced stamen length and exhibit male sterility relative to the wild-type plants. We show that these effects may arise from gibberellin (GA)-signaling defects. The signaling pathway of bioactive GAs depends on the proteolysis of their repressors, DELLA proteins. The repressor GA (RGA) DELLA protein represses plant growth, inflorescence, and flower and seed development. Our molecular data indicate that GCN5 is required for the activation and H3K14 acetylation of genes involved in the late stages of GA biosynthesis and catabolism. We studied the genetic interaction of the RGA and GCN5; the RGA can partially suppress GCN5 action during the whole plant life cycle. The reduced elongation of the stamen filament of gcn5–6 mutants is reversed in the rga–t2;gcn5–6 double mutants. RGAs suppress the GCN5 effect on the gene expression and histone acetylation of GA catabolism and GA signaling. Interestingly, the RGA and RGL2 do not suppress ADA2b function, suggesting that ADA2b acts downstream of GA signaling and is distinct from GCN5 activity. In conclusion, we propose that the action of GCN5 on stamen elongation is partially mediated by RGA and GA signaling.

Histone acetyltransferases (HAT) modify the amino-terminal tails of the core histone proteins via acetylation, regulating chromatin structure and transcription. The GENERAL CONTROL NON-DEREPRESSIBLE 5 (GCN5) is a HAT that specifically acetylates H3K14 residues. GCN5 has been associated with cell division and differentiation, meristem function, root, stem, foliar and floral development, and plant environmental response. The flowers of gcn5–6 plants display reduced length of stamen and exhibit male sterility relative to the wild-type plants. We show these effects may arise from gibberellin (GA) signaling defects. The signaling pathway of bioactive GAs depends on the proteolysis of their repressors, DELLA proteins. The DELLA protein, REPRESSOR OF GA (RGA), represses plant growth, inflorescence, flower and seed development. Our molecular data indicate that GCN5 is required for activation and H3K14 acetylation of genes involved in the late stages of GA biosynthesis and catabolism. We studied the genetic interaction of RGA and GCN5; RGA can partially suppress GCN5 action. The reduced elongation of the stamen filament of gcn5–6 mutants is reversed in the rga–t2;gcn5–6 double mutants. This mechanism involved suppressing the GCN5 effect on the expression and histone acetylation in GAI -locus by RGA. Interestingly, RGA and RGL2 do not suppress ADA2b function, suggesting that ADA2b acts downstream in GA signaling and is distinct from GCN5 activity. In conclusion, we propose that the action of GCN5 on stamen elongation is mediated partially by RGA and GA signaling.

The genus Hypericum, which comprises over 450 species worldwide, has a long history of use in traditional medicine. It is now known for its antidepressant, antiviral, antibacterial, and anticancer properties. This review summarizes the current knowledge on the biosynthesis of the main bioactive secondary metabolites responsible for the pharmaceutical applications of plants, particularly hypericin and hyperforin. In addition, this review highlights the importance of other chemical constituents in Hypericum, such as xanthones and flavonoids, which contribute to the pharmacological potential of the genus. Hypericin, a naphthodianthrone, has been shown to have remarkable pharmacological effects, particularly as a potential anticancer agent. On the other hand, hyperforin, a polyprenylated acylphloroglucinol, has been identified as a potent antidepressant. Recent advances in transcriptomics, metabolomics, and genomics have identified novel genes and enzymatic pathways that facilitate the biosynthesis of these compounds, providing valuable insights into their formation. Despite these advances, further research is essential to fully characterize the biosynthetic pathways and optimize the production of bioactive compounds in Hypericum species.