Indole-3-acetaldoxime delays root iron-deficiency responses and modify auxin homeostasis in Medicago truncatula

Regulatory Peptide Encoded by the Primary Transcript of miR396a Influences Gene Expression and Root Development in Solanum lycopersicum

MicroRNAs (miRNAs) are the processing products of primary miRNAs (pri-miRNAs) that regulate the expression of target genes. Recent studies have demonstrated that some pri-miRNAs can encode small peptides (miPEPs) that perform significant biological functions. The function of miPEPs in tomatoes, an important model horticultural crop, remains to be investigated. Here, we characterized the primary sequence of tomato miR396a using 5' RACE and confirmed the presence of miPEP396a in tomato by verifying the translational activity of the start codon. It primarily resides in the nucleus to exert its function and additionally regulates the expression of pri-miR396a, miR396a, and its target genes. Transcriptomic and metabolomic analyses showed that in vitro synthesis of miPEP396a significantly increased the expression of genes related to phenylpropanoid biosynthesis and hormones in tomato. Meanwhile, our in vitro application of miPEP396a in tomato significantly inhibited the elongation of tomato primary roots. In conclusion, our results indicate that miPEP396a regulates root growth in tomato by specifically promoting miR396a expression, provide insight into the function of miPEPs in tomato and potential applications.

A new oxidative pathway of nitric oxide production from oximes in plants

Nitric oxide (NO) is an essential reactive oxygen species and a signal molecule in plants. Although several studies have proposed the occurrence of oxidative NO production, only reductive routes for NO production, such as the nitrate (NO-3) -upper-reductase pathway, have been evidenced to date in land plants. However, plants grown axenically with ammonium as the sole source of nitrogen exhibit contents of nitrite and NO3-, evidencing the existence of a metabolic pathway for oxidative production of NO. We hypothesized that oximes, such as indole-3-acetaldoxime (IAOx), a precursor to indole-3-acetic acid, are intermediate oxidation products in NO synthesis. We detected the production of NO from IAOx and other oximes catalyzed by peroxidase (POD) enzyme using both 4-amino-5-methylamino-2',7'-difluorescein fluorescence and chemiluminescence. Flavins stimulated the reaction, while superoxide dismutase inhibited it. Interestingly, mouse NO synthase can also use IAOx to produce NO at a lower rate than POD. We provided a full mechanism for POD-dependent NO production from IAOx consistent with the experimental data and supported by density functional theory calculations. We showed that the addition of IAOx to extracts from Medicago truncatula increased the in vitro production of NO, while in vivo supplementation of IAOx and other oximes increased the number of lateral roots, as shown for NO donors, and a more than 10-fold increase in IAOx dehydratase expression. Furthermore, we found that in vivo supplementation of IAOx increased NO production in Arabidopsis thaliana wild-type plants, while prx33-34 mutant plants, defective in POD33-34, had reduced production. Our data show that the release of NO by IAOx, as well as its auxinic effect, explain the superroot phenotype. Collectively, our study reveals that plants produce NO utilizing diverse molecules such as oximes, POD, and flavins, which are widely distributed in the plant kingdom, thus introducing a long-awaited oxidative pathway to NO production in plants. This knowledge has essential implications for understanding signaling in biological systems.