In Arabidopsis thaliana, the final step of floral organ abscission is regulated by INFLORESCENCE DEFICIENT IN ABSCISSION (IDA): ida mutants fail to abscise floral organs, and plants overexpressing IDA display earlier abscission. We show that five IDA-LIKE (IDL) genes are expressed in different tissues, but plants overexpressing these genes have phenotypes similar to IDA-overexpressing plants, suggesting functional redundancy. IDA/IDL proteins have N-terminal signal peptides and a C-terminal conserved motif (extended PIP [EPIP]) at the C terminus (EPIP-C). IDA can, similar to CLAVATA3, be processed by an activity from cauliflower meristems. The EPIP-C of IDA and IDL1 replaced IDA function in vivo, when the signal peptide was present. In addition, synthetic IDA and IDL1 EPIP peptides rescued ida and induced early floral abscission in wild-type flowers. The EPIP-C of the other IDL proteins could partially substitute for IDA function. Similarly to ida, a double mutant between the receptor-like kinases (RLKs) HAESA (HAE) and HAESA-LIKE2 (HSL2) displays nonabscising flowers. Neither overexpression of IDA nor synthetic EPIP or EPIP-C peptides could rescue the hae hsl2 abscission deficiency. We propose that IDA and the IDL proteins constitute a family of putative ligands that act through RLKs to regulate different events during plant development.

Throughout their life cycle, plants produce new organs, such as leaves, flowers, and lateral roots. Organs that have served their purpose may be shed after breakdown of primary cell walls between adjacent cell files at the site of detachment. In Arabidopsis , floral organs abscise after pollination, and this cell separation event is controlled by the peptide INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), which signals through the leucine-rich repeat receptor-like kinases HAESA (HAE) and HAESA-LIKE2 (HSL2). Emergence of new lateral root primordia, initiated deep inside the root under the influence of auxin, is similarly dependent on cell wall dissolution between cells in the overlaying endodermal, cortical, and epidermal tissues. Here we show that this process requires IDA , HAE , and HSL2 . Mutation in these genes constrains the passage of the growing lateral root primordia through the overlaying layers, resulting in altered shapes of the lateral root primordia and of the overlaying cells. The HAE and HSL2 receptors are redundant in function during floral organ abscission, but during lateral root emergence they are differentially involved in regulating cell wall remodeling genes. In the root, IDA is strongly auxin-inducible and dependent on key regulators of lateral root emergence—the auxin influx carrier LIKE AUX1-3 and AUXIN RESPONSE FACTOR7. The expression levels of the receptor genes are only transiently induced by auxin, suggesting they are limiting factors for cell separation. We conclude that elements of the same cell separation signaling module have been adapted to function in different developmental programs.

Floral organ abscission in Arabidopsis thaliana is regulated by the putative ligand-receptor system comprising the signaling peptide INFLORESCENCE DEFICIENT IN ABSCISSION (IDA) and the two receptor-like kinases HAESA and HAESA-LIKE2. The IDA signaling pathway presumably activates a MITOGEN-ACTIVATED PROTEIN KINASE (MAPK) cascade to induce separation between abscission zone (AZ) cells. Misexpression of IDA effectuates precocious floral abscission and ectopic cell separation in latent AZ cell regions, which suggests that negative regulators are in place to prevent unrestricted and untimely AZ cell separation. Through a screen for mutations that restore floral organ abscission in ida mutants, we identified three new mutant alleles of the KNOTTED-LIKE HOMEOBOX gene BREVIPEDICELLUS (BP)/KNOTTED-LIKE FROM ARABIDOPSIS THALIANA1 (KNAT1). Here, we show that bp mutants, in addition to shedding their floral organs prematurely, have phenotypic commonalities with plants misexpressing IDA, such as enlarged AZ cells. We propose that BP/KNAT1 inhibits floral organ cell separation by restricting AZ cell size and number and put forward a model whereby IDA signaling suppresses BP/KNAT1, which in turn allows KNAT2 and KNAT6 to induce floral organ abscission.

Plant roots are important for a wide range of processes, including nutrient and water uptake, anchoring and mechanical support, storage functions, and as the major interface with the soil environment. Several small signalling peptides and receptor kinases have been shown to affect primary root growth, but very little is known about their role in lateral root development. In this context, the CLE family, a group of small signalling peptides that has been shown to affect a wide range of developmental processes, were the focus of this study. Here, the expression pattern during lateral root initiation for several CLE family members is explored and to what extent CLE1, CLE4, CLE7, CLE26, and CLE27, which show specific expression patterns in the root, are involved in regulating root architecture in Arabidopsis thaliana is assessed. Using chemically synthesized peptide variants, it was found that CLE26 plays an important role in regulating A. thaliana root architecture and interacts with auxin signalling. In addition, through alanine scanning and in silico structural modelling, key residues in the CLE26 peptide sequence that affect its activity are pinpointed. Finally, some interesting similarities and differences regarding the role of CLE26 in regulating monocot root architecture are presented.

Multidrug-resistant (MDR) bacteria pose a major threat to public health, and additional sources of antibacterial candidates are urgently needed. Noncanonical peptides (NCPs), derived from noncanonical small open reading frames, represent small biological molecules with important roles in biology. However, the antibacterial activity of NCPs remains largely unknown. Here, we discovered a plant-derived noncanonical antibacterial peptide (NCBP1) against both Gram-positive and Gram-negative bacteria. NCBP1 is composed of 11 amino acid residues with cationic surface potential and favorable safety and stability. Mechanistic studies revealed that NCBP1 displayed antibacterial activity by targeting phosphatidylglycerol and cardiolipin in bacterial membrane, resulting in membrane damage and dysfunction. Notably, NCBP1 showed promising efficacy in mice. Furthermore, NCBP1 effectively inhibited the growth of plant fungal pathogens and enhanced disease resistance in maize. Our results demonstrate the unexplored antimicrobial potential of plant-derived NCPs and provide an accessible source for the discovery of antimicrobial substances against MDR bacterial and fungal pathogens.