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Lateral roots (LRs) increase root surface area and allow plants greater access to soil water and nutrients. LR formation is tightly regulated by the phytohormone auxin. Whereas the transcription factor ETHYLENE-RESPONSIVE ELEMENT BINDING FACTOR13 (ERF13) prevents LR emergence in Arabidopsis (Arabidopsis thaliana), auxin activates MITOGEN-ACTIVATED PROTEIN KINASE14 (MPK14), which leads to ERF13 degradation and ultimately promotes LR emergence. In this study, we discovered interactions between ERF13 and the E3 ubiquitin ligases MOS4-ASSOCIATED COMPLEX 3A (MAC3A) and MAC3B. As MAC3A and MAC3B gradually accumulate in the LR primordium, ERF13 levels gradually decrease. We demonstrate that MAC3A and MAC3B ubiquitinate ERF13, leading to its degradation and accelerating the transition of LR primordia from stages IV to V. Auxin enhances the MAC3A and MAC3B interaction with ERF13 by facilitating MPK14-mediated ERF13 phosphorylation. In summary, this study reveals the molecular mechanism by which auxin eliminates the inhibitory factor ERF13 through the MPK14-MAC3A and MAC3B signaling module, thus promoting LR emergence. Auxin removes the barrier protein ERF13 through the MPK14-MAC3A and MAC3B signaling module, thus promoting lateral root emergence. [ABSTRACT FROM AUTHOR]

Gravitropism is an essential adaptive response of land plants. Asymmetric auxin gradients across plant organs, interpreted by multiple auxin signaling components including AUXIN RESPONSE FACTOR7 (ARF7), trigger differential growth and bending response. However, how this fundamental process is strictly maintained in nature remains unclear. Here, we report that gravity stimulates the transcription of METHYL ESTERASE17 (MES17) along the lower side of the hypocotyl via ARF7‐dependent auxin signaling. The asymmetric distribution of MES17, a methyltransferase that converts auxin from its inactive form methyl indole‐3‐acetic acid ester (MeIAA) to its biologically active form free‐IAA, enhanced the gradient of active auxin across the hypocotyl, which in turn reversely amplified the asymmetric auxin responses and differential growth that shape gravitropic bending. Taken together, our findings reveal the novel role of MES17‐mediated auxin homeostasis in gravitropic responses and identify an ARF7‐triggered feedback mechanism that reinforces the asymmetric distribution of active auxin and strictly controls gravitropism in plants. [ABSTRACT FROM AUTHOR]

Plant growth promoting rhizobacteria (PGPR) refer to bacteria that colonize the rhizosphere and contribute to plant growth or stress tolerance. To further understand the molecular mechanism by which PGPR exhibit symbiosis with plants, we performed a high-throughput single colony screening from the rhizosphere, and uncovered a bacterium (named promoting lateral root, PLR) that significantly promotes Arabidopsis lateral root formation. By 16S rDNA sequencing, PLR was identified as a novel sub-species of Serratia marcescens. RNA-seq analysis of Arabidopsis integrated with phenotypic verification of auxin signalling mutants demonstrated that the promoting effect of PLR on lateral root formation is dependent on auxin signalling. Furthermore, PLR enhanced tryptophan-dependent indole-3-acetic acid (IAA) synthesis by inducing multiple auxin biosynthesis genes in Arabidopsis. Genome-wide sequencing of PLR integrated with the identification of IAA and its precursors in PLR exudates showed that tryptophan treatment significantly enhanced the ability of PLR to produce IAA and its precursors. Interestingly, PLR induced the expression of multiple nutrient (N, P, K, S) transporter genes in Arabidopsis in an auxin-independent manner. This study provides evidence of how PLR enhances plant growth through fine-tuning auxin biosynthesis and signalling in Arabidopsis, implying a potential application of PLR in crop yield improvement through accelerating root development. [ABSTRACT FROM AUTHOR]

Auxin response factors (ARFs) play important roles in plant growth and development; however, research in peanut (Arachis hypogaea L.) is still lacking. Here, 63, 30, and 30 AhARF genes were identified from an allotetraploid peanut cultivar and two diploid ancestors (A. duranensis and A. ipaensis). Phylogenetic tree and gene structure analysis showed that most AhARFs were highly similar to those in the ancestors. By scanning the whole-genome for ARF-recognized cis-elements, we obtained a potential target gene pool of AhARFs, and the further cluster analysis and comparative analysis showed that numerous members were closely related to root development. Furthermore, we comprehensively analyzed the relationship between the root morphology and the expression levels of AhARFs in 11 peanut varieties. The results showed that the expression levels of AhARF14/26/45 were positively correlated with root length, root surface area, and root tip number, suggesting an important regulatory role of these genes in root architecture and potential application values in peanut breeding. [ABSTRACT FROM AUTHOR]

Summary: Maize height is determined by the number of nodes and the length of internodes. Node number is driven by intercalary meristem formation and internode length by intercalary cell elongation, respectively. However, mechanisms regulating establishment of nodes and internode growth are unclear. We screened EMS‐induced maize mutants and identified a dwarf mutant zm66, linked to a single base change in TERMINAL EAR 1 (ZmTE1). Detailed phenotypic analysis revealed that zm66 (zmte1‐2) has shorter internodes and increased node numbers, caused by decreased cell elongation and disordered intercalary meristem formation, respectively. Transcriptome analysis showed that auxin signalling genes are also dysregulated in zmte1‐2, as are cell elongation and cell cycle‐related genes. This argues that ZmTE1 regulates auxin signalling, cell division, and cell elongation. We found that the ZmWEE1 kinase phosphorylates ZmTE1, thus confining it to the nucleus and probably reducing cell division. In contrast, the ZmPP2Ac‐2 phosphatase promotes dephosphorylation and cytoplasmic localization of ZmTE1, as well as cell division. Taken together, ZmTE1, a key regulator of plant height, is responsible for maintaining organized formation of internode meristems and rapid cell elongation. ZmWEE1 and ZmPP2Ac‐2 might balance ZmTE1 activity, controlling cell division and elongation to maintain normal maize growth. [ABSTRACT FROM AUTHOR]

Auxin, one of the first identified and most widely studied phytohormones, has been and will remain a hot topic in plant biology. After more than a century of passionate exploration, the mysteries of its synthesis, transport, signaling, and metabolism have largely been unlocked. Due to the rapid development of new technologies, new methods, and new genetic materials, the study of auxin has entered the fast lane over the past 30 years. Here, we highlight advances in understanding auxin signaling, including auxin perception, rapid auxin responses, TRANSPORT INHIBITOR RESPONSE 1 and AUXIN SIGNALING F‐boxes (TIR1/AFBs)‐mediated transcriptional and non‐transcriptional branches, and the epigenetic regulation of auxin signaling. We also focus on feedback inhibition mechanisms that prevent the over‐amplification of auxin signals. In addition, we cover the TRANSMEMBRANE KINASE‐mediated non‐canonical signaling, which converges with TIR1/AFBs‐mediated transcriptional regulation to coordinate plant growth and development. The identification of additional auxin signaling components and their regulation will continue to open new avenues of research in this field, leading to an increasingly deeper, more comprehensive understanding of how auxin signals are interpreted at the cellular level to regulate plant growth and development. [ABSTRACT FROM AUTHOR]

Protein–protein interaction (PPI) network analysis is an effective method to identify key proteins during plant development, especially in species for which basic molecular research is lacking, such as apple (Malus domestica). Here, an MdPPI network containing 30 806 PPIs was inferred in apple and its quality and reliability were rigorously verified. Subsequently, a root‐growth subnetwork was extracted to screen for critical proteins in root growth. Because hormone‐related proteins occupied the largest proportion of critical proteins, a hormone‐related sub‐subnetwork was further extracted from the root‐growth subnetwork. Among these proteins, auxin‐related M. domestica TRANSPORT INHIBITOR RESISTANT 1 (MdTIR1) served as the central, high‐degree node, implying that this protein exerts essential roles in root growth. Furthermore, transgenic apple roots overexpressing an MdTIR1 transgene displayed increased primary root elongation. Expression analysis showed that MdTIR1 significantly upregulated auxin‐responsive genes in apple roots, indicating that it mediates root growth in an auxin‐dependent manner. Further experimental validation revealed that MdTIR1 interacted with and accelerated the degradation of MdIAA28, MdIAA43, and MdIAA46. Thus, MdTIR1‐mediated degradation of MdIAAs is critical in auxin signal transduction and root growth regulation in apple. Moreover, our network analysis and high‐degree node screening provide a novel research technique for more generally characterizing molecular mechanisms. [ABSTRACT FROM AUTHOR]

Auxin plays a critical role in lateral root (LR) formation. The signaling module composed of auxin-response factors (ARFs) and lateral organ boundaries domain transcription factors mediates auxin signaling to control almost every stage of LR development. Here, we show that auxin-induced degradation of the APETALA2/Ethylene Responsive Factor (AP2/ERF) transcription factor ERF13, dependent on MITOGEN-ACTIVATED PROTEIN KINASE MPK14-mediated phosphorylation, plays an essential role in LR development. Overexpression of ERF13 results in restricted passage of the LR primordia through the endodermal layer, greatly reducing LR emergence, whereas the erf13 mutants showed an increase in emerged LR. ERF13 inhibits the expression of 3-ketoacyl-CoA synthase16 (KCS16), which encodes a fatty acid elongase involved in very-long-chain fatty acid (VLCFA) biosynthesis. Overexpression of KCS16 or exogenous VLCFA treatment rescues the LR emergence defects in ERF13 overexpression lines, indicating a role downstream of the auxin–MPK14–ERF13 signaling module. Collectively, our study uncovers a novel molecular mechanism by which MPK14-mediated auxin signaling modulates LR development via ERF13-regulated VLCFA biosynthesis. Auxin plays a critical role in lateral root (LR) formation. Recent studies suggest that mitogen-activated protein kinases 3/6 (MPK3/6) play important roles in auxin-regulated LR development. The downstream regulators of MPK3/6-regulated LR development are still largely unknown, and it is unclear whether other MPKs are also involved in auxin-regulated LR development. Our study uncovers a novel molecular mechanism of MPK14-mediated auxin signaling in LR development via ERF13 regulation of very-long-chain fatty acid biosynthesis. [ABSTRACT FROM AUTHOR]