Auxin Immunolocalization in Coffea canephora Tissues

Cellular responses of oil palm genotypes during somatic embryogenesis involve participation of procambial cells, DNA demethylation, and auxin accumulation

Cell markers of somatic embryogenesis initiation from leaf tissues in oil palm involve the participation of procambial cells, DNA demethylation, and auxin accumulation. Low callogenesis and genotype-dependent response have been mentioned in the development of somatic embryogenesis protocols of Elaeis oleifera × E. guineensis elite hybrids, which requires more detailed investigations of the process. Thus, the initial cellular responses of immature leaves of adult genotypes of this hybrid were investigated for the first time, emphasizing histological, epigenetic, and endogenous auxin changes. Leaf segments from two genotypes, one responsive to somatic embryogenesis (B351733) and another non-responsive (B352933), were inoculated in Murashige and Skoog medium with 450 µM of 4-amino-3, 5, 6-trichloropicolinic acid. For anatomical analysis, samples of both genotypes were collected at 0, 20, 90, and 105 days of cultivation. Samples of both genotypes were also taken at different cultivation periods to analyze DNA methylation status (% 5-mC-5 methylcytosine) via ELISA test. Immunolocalization assays were performed with anti-indole-3-acetic acid and anti-5-methyl-deoxycytosine antibodies from samples of hybrid B351733. We distinguished two groups of cells reactive to the induction of embryogenic callogenesis, parenchymatous sheath cells, and procambial cells; however, only the latter are directly involved with the formation of calluses. The data obtained indicate that the formation of calluses in hybrid B351733 is related to DNA hypomethylation, while the non-responsiveness of leaf explants in hybrid B352932 is related to DNA hypermethylation. The in situ immunolocalization enabled the identification of initial markers of the callogenic process, such as IAA accumulation and hypomethylation. Identifying these events brings the possibility of establishing strategies for efficient manipulation of somatic embryogenesis protocols in palm trees.

Identification, analysis, and modeling of the YUCCA protein family genome-wide in Coffea canephora

Auxin is involved in almost every aspect of plant growth and development, from embryogenesis to senescence. Indole-3-acetic acid (IAA) is the main known natural auxin that is synthesized by enzymes tryptophan aminotransferase of arabidopsis (TAA) and YUCCA (YUC) of the flavin-containing monooxygenases family (FMO) from one of the tryptophan-dependent pathways. Genome-wide identification and comprehensive analysis of the YUC-protein family have been conducted in Coffea canephora in the present study. A total of 10 members CcYUC gene family were identified in C. canephora. Phylogenetic analysis revealed that the CcYUC protein family is evolutionarily conserved, and they consist of four groups. In contrast, bioinformatic analysis predicted a hydrophobic transmembrane helix (TMH) for one CcYUC (YUC10) member only. Isoelectric point (pI), molecular mass (Ms), signal peptide, subcellular localization, and phosphorylation sites were predicted for CcYUC proteins. YUC enzymes require the prosthetic group flavin adenine dinucleotide (FAD) and the cofactor nicotinamide adenine dinucleotide phosphate (NADPH) for their enzymatic activity. Therefore, we include the molecular docking for CcYUC2-FAD-NADPH-IPyA and yucasin, which is a specific inhibitor for YUC activity. The docking results showed FAD and NADPH binding at the big and small domain sites, respectively, in CcYUC2. IPyA binds very close to FAD along the big domain, and yucasin competes for the same site as IPA, blocking IAA production. Furthermore, in silico point mutations affect the stability of the CcYUC2-4 proteins.

Two MADS-box genes regulate vascular cambium activity and secondary growth by modulating auxin homeostasis in Populus

In trees, stem secondary growth depends on vascular cambium proliferation activity and subsequent cell differentiation, in which an auxin concentration gradient across the cambium area plays a crucial role in regulating the process. However, the underlying molecular mechanism for the establishment of auxin concentration is not fully understood. In this study, we identified two function-unknown MADS-box genes, VCM1 and VCM2, which are expressed specifically in the vascular cambium and modulate the subcellular homeostasis of auxin. Simultaneous knockdown of both VCM1 and VCM2 enhanced vascular cambium proliferation activity and subsequent xylem differentiation. Overexpression of VCM1 suppressed vascular cambium activity and wood formation by regulating PIN5 expression, which tuned the soluble auxin concentration in the vascular cambium area. This study reveals the role of VCM1 and VCM2 in regulating the proliferation activity of the vascular cambium and secondary growth by modulating the subcellular auxin homeostasis in Populus.

Abscisic Acid Regulates the Root Growth Trajectory by Reducing Auxin Transporter PIN2 Protein Levels in Arabidopsis thaliana

The root is in direct contact with soil. Modulation of root growth in response to alterations in soil conditions is pivotal for plant adaptation. Extensive research has been conducted concerning the adjustment of root elongation and architecture in response to environmental factors. However, little is known about the modulation of the root growth trajectory, as well as its hormonal mechanism. Here we report that abscisic acid (ABA) participated in controlling root growth trajectory. The roots upon ABA treatment or from ABA-accumulation double mutant cyp707a1,3 exhibit agravitropism-like growth pattern (wavy growth trajectory). The agravitropism-like phenotype is mainly ascribed to the compromised shootward transportation of auxin since we detected a reduced fluorescence intensity of auxin reporter DR5:VENUS in the root epidermis upon exogenous ABA application or in the endogenous ABA-accumulation double mutant cyp707a1,3. We then tried to decipher the mechanism by which ABA suppressed shootward auxin transport. The membrane abundance of PIN2, a facilitator of shootward auxin transport, was significantly reduced following ABA treatment and in cyp707a1,3. Finally, we revealed that ABA reduced the membrane PIN2 intensity through suppressing the PIN2 expression rather than accelerating PIN2 degradation. Ultimately, our results suggest a pivotal role for ABA in the root growth trajectory and the hormonal interactions orchestrating this process.