The phytohormone auxin (Aux) is a principal endogenous developmental signal in plants. It mediates transcriptional reprogramming by a well-established canonical signalling mechanism. TIR1/AFB auxin receptors are F-box subunits of an ubiquitin ligase complex; after auxin perception, they associate with Aux/IAA transcriptional repressors and ubiquitinate them for degradation, thus enabling the activation of auxin response factor (ARF) transcription factors. Here we revise this paradigm by showing that without TIR1 adenylate cyclase (AC) activity, auxin-induced degradation of Aux/IAAs is not sufficient to mediate the transcriptional auxin response. Abolishing the TIR1 AC activity does not affect auxin-induced degradation of Aux/IAAs but renders TIR1 non-functional in mediating transcriptional reprogramming and auxin-regulated development, including shoot, root, root hair growth and lateral root formation. Transgenic plants show that local cAMP production in the vicinity of the Aux/IAA-ARF complex by unrelated AC enzymes bypasses the need for auxin perception and is sufficient to induce ARF-mediated transcription. These discoveries revise the canonical model of auxin signalling and establish TIR1/AFB-produced cAMP as a second messenger essential for transcriptional reprograming.

Microbiota transplantation is a strong tool for managing plant disease. This study investigates the effects of microbiota transplantation on Cotton Leaf Curl Disease (CLCuD) resistance in Gossypium hirsutum, a species with good fiber length but high susceptibility to biotic stresses. Using metabarcoding for V3-V4 16S rRNA gene amplicon, microbial fractions from both rhizosphere and phyllosphere of CLCuD-resistant species Gossypium arboreum, and susceptible cotton varieties are analyzed. Unique bacterial taxa have been identified associated with disease resistance. Interspecies and intraspecies microbiota transplantation is conducted, followed by CLCuD incidence assays. It is seen that rhizospheric microbiota transplantation from G. arboreum FDH228 significantly suppresses CLCuD in G. hirsutum varieties, outperforming exogenous salicylic acid application. While phyllospheric transplants also reduce disease incidence, they are less effective than rhizospheric transplants. Differential expression analysis DESeq2 is utilized to identify key bacterial genera correlated with CLCuD suppression, including Pseudoxanthomonas and Stenotrophomonas in the rhizosphere of G. arboreum FDH228. Functional pathway analysis reveals upregulation of stress response and metabolism in tolerant species. Transcriptomics reveals upregulation of genes involved in protein phosphorylation and stress response in interspecies rhizospheric microbiota transplants. This study highlights microbiota transplantation as a sustainable method for controlling CLCuD along with specific microbial and genetic mechanisms contributing to CLCuD resistance.

Auxin has emerged as a crucial regulator of plant nitrogen (N)-use efficiency (NUE) through indirect effects on plant growth and development and direct regulation of N metabolism-related genes. We previously reported DULL NITROGEN RESPONSE1 (DNR1) as an amino transferase that inhibits auxin accumulation and negatively regulates rice (Oryza sativa) NUE and grain yield. However, the identities of molecular regulators acting upstream of DNR1 await exploration. Our current work identifies SUPPRESSOR OF DNR1 ON CHROMOSOME 5 (SOD5) from a DNR1 suppressor mutant. SOD5 encodes a v-myb avian myeloblastosis viral oncogene homolog (MYB) transcription factor that directly binds to the DNR1 promoter, activating its expression and further repressing auxin accumulation. Knocking out SOD5 significantly increases NUE and grain yield, especially under low N conditions. Therefore, targeting SOD5 offers a promising strategy for enhancing crop performance, supporting the development of crops better suited for sustainable agriculture.