mIDA-induced [Ca2+]cyt release in Arabidopsis roots correlates with pHAE and pHSL2 activity

a, Normalized R-GECO1 fluorescence intensities (ΔF/F) were measured from regions of interest (ROI) (upper panel, outlined in red) in the meristematic and elongation zone of the root. Fluorescence intensities (ΔF/F) over time of the whole root represented in a heat map (lower panel). Shown are cytosolic calcium concentration ([Ca2+]cyt) dynamics in the ROI in response to 1 mM mIDA over time. (see also Movie 1). Red lines at 5 minutes (min) indicates application of mIDA peptide or application of eATP at 22 min. Representative response from 10 roots. The increase in [Ca2+]cyt response propagates through the roots as two waves. b, For comparison; Normalized R-GECO1 fluorescence intensities (ΔF/F) measured from regions of interest (ROI) (outlined in red, upper panel) in response to 1μM flg22 over time. Fluorescence intensities (ΔF/F) over time of the whole root represented in a heat map (lower panel). Red line at 0 min (min) indicates application of flg22 peptide. Representative response from 10 roots. The increase in [Ca2+]cyt response propagates through the roots as a single wave seen as normalized R-GECO1 fluorescence intensities (ΔF/F) shown as a heat map (see also movie 2). c,d,e, Expression of the receptors c, pHAE:Venus-H2B d, pHSL2:Venus-H2B and e, pFLS2:Venus-H2B in 7 days-old roots. Representative pictures of n = 8. Scale bar = 50 µm, single plane image, magenta = propidium iodide stain.

mIDA-induced [Ca2+]cyt release in Arabidopsis abscission zones.

a, Normalized R-GECO1 fluorescence intensities (ΔF/F) were measured from regions of interest (ROI) (outlined in red) in floral abscission zone (AZ)s. Shown are cytosolic calcium concentration ([Ca2+]cyt) dynamics in the ROI in response to 1 µM mIDA over time (see also Movie 3). Representative response from 10 flowers. Red lines at 5 minutes (min) indicates application of mIDA peptide or application of eATP at 35 min (for AZs), respectively. The increase in [Ca2+]cyt response propagates through the AZ as a single wave. b,Expression of pHAE:Venus-H2B and pHSL2:Venus-H2B in flowers at position 6 (See Sup Fig. 4a for positions) (arrowhead indicates AZ). Representative pictures of n = 8, scale bar = 100 µm, maximum intensity projections of z-stacks. b Expression of pHAE:Venus-H2B and pHSL2:Venus-H2B in flower position 6 (See Sup. Fig.4a for positions) (arrowhead indicates AZ). Representative picture of n = 8. Scale bar = 100 µm, maximum intensity projections of z-stacks.

IDA is induced by biotic and abiotic stress

Representative pictures of pIDA:GUS expression after 12 h treatment with 1 µM flg22, chitin, NaCl, Mannitol and 1 µM IDAΔN69 in a, cells surrounding emerging lateral roots, and b, in the main root. c, Normalized emitted fluorescence of fluorochrome 4-methyl umbelliferone (4-MU) in 7 days-old seedlings after 12 h treatment with 1 µM flg22, chitin, NaCl, Mannitol and 1 µM of the inactive IDA peptide, IDAΔN69. Normalized to 1 on No Treatment sample. Controls were not subjected to any stimuli (No treatment). n = 6, experiment repeated 3 times. * = significantly different from the non-treated (No treatment) sample (p < 0.05, student t-test, two tailed). Controls were not subjected to any stimuli (No treatment). a,b, Representative picture of n = 10, experiment repeated 3 times, scale bar = 50 μm.

Callose deposition is not induced by mIDA

a, No callose deposition could be detected in Col-0 WT and fls2 mutants treated with water (mock treatment) or 1 µM mIDA. Callose deposition could be observed in cotyledons of eight day old Col-0 WT seedlings treated with 1 µM flg22. No callose deposition could be detected in fls2 mutant treated with flg22. Representative images of 9-12 seedlings per genotype. b, Total callose deposition area for the different genotypes treated with water (mock treatment), 1 µM mIDA or 1 µM flg22. Statistical significant difference at (p < 1*10^-6). N = 9-12

mIDA induced expression of defense-associated marker genes

a, Transcripts of FRK1, MYB51, and PEP3 in WT Col-0 seedlings exposed to 1 µM mIDA for 1 h (light gray) and to 1 µM mIDA for 12 h (dark gray) compared to untreated tissue (black). RNA levels were measured by RT-qPCR analysis. ACTIN was used to normalize mRNA levels. n = 4, three biological replicates Statistical analyses was performed comparing induction times of individual genes using one-way ANOVA and post-hoc Tukey’s test (p < 0.05). b,pMYB51:YFPN expression is enhanced in roots after 7 h exposure to 1 μM mIDA peptide compared to untreated roots (control), scale bar = 50 μm, maximum intensity projections of z-stacks, magenta = propidium iodide stain.

mIDA and flg22 co-treatement extremely enhances the expression of defense-associated marker genes

a, RT-qPCR data showing transcription of FRK1, MYB51, and PEP3 in Col-0 WT seedlings exposed to 1 µM mIDA, 1 µM flg22 or a combination of 1 µM mIDA and 1 µM flg22 for 1 h compared to untreated seedlings (No treatment control). ACTIN was used to normalize mRNA levels. Figure represent 3 biological replicates with 4 technical replicates. Statistical analyses comparing No Treatment to peptide treated samples was performed using one-way ANOVA and post-hoc Tukey’s test (p < 0.05).

IDA regulates cell separation processes, but is also involved in major transcription of defense genes upon pathogen attack.

a, IDA and the IDL peptides control cell separation processes during plant development and in response to abiotic and biotic stress (Butenko et al. 2003; Patharkar and Walker 2016; Patharkar et al. 2017; Shi et al. 2018). Tissue undergoing cell separation includes floral organ abscission, cauline leaf abscission, emerging of lateral roots and root cap sloughing. b, During normal conditions, IDA control floral organ abscission and emergence of lateral roots by relaying a signal through receptor complexes including HAE, HSL2, SERK1 and BAK1 to modulate the expression of cell wall remodeling (CWR) genes as well as moderately expression of defense genes. IDA activates a receptor dependent production of ROS and an increase in [Ca2+]cyt. b, Upon stress, such as pathogen attack, the activation of HAE and HSL2 acts in addition to activation of defense related receptors, such as FLS2, to enhance the expression of defense related genes significantly. This ensure optimal protection of cells undergoing cell separation, which may be major entry routes during a pathogen attack.

Peptide sequences

Primers sequences and function

IDA induces a production of ROS in Arabidopsis

a, ROS production detected by the luminol-based assay was monitored over time as RLU. ROS production from hae hsl2 leaf disks expressing 35S:HAE-YFP in response to 1 μM mIDA (black) and in WT control (blue). b, Fluorescent image of hae hsl2 rosette leaves expressing 35S:HAE:YFP. Signal is detected in the plasma membrane of cells in the epidermal layer. Representative picture. Scale bar = 50 μm. c, 35S:HAE-YFP complements the hae hsl2 mutant abscission phenotype of observed. Scale = 1 cm.

The IDA triggered increase in [Ca2+]cyt is receptor dependent and is abolished in the presence of Ca2+ inhibitors

a, Increase in [Ca2+]cyt in seedlings expressing the cytosolic localized Aequorin-based luminescence Ca2+ sensor (Aeq) measured in relative light units (RLU) treated with 1 μM mIDA (black). No response is observed in Aeq seedlings treated with 1 μM IDAΔN69 (gray) or in hae hsl2 Aeq seedlings treated with 1 μM mIDA (blue). b, Increase in [Ca2+]cyt in seedlings expressing the cytosolic localized Aequorin-based luminescence Ca2+ sensor (Aeq) measured in relative light units (RLU) treated with 1 μM mIDA. No response is observed in Aeq seedlings treated with 1 mM EGTA (blue) or 1mM LaCl3 (grey). Curves represent average of 3 independent experiments with 4-6 replicates in each experiment.

mIDA induces a Ca2+ response in flowers

a, Arabidopsis flowers and siliques at different developmental stages. Flowers along the main inflorescence are counted from the first flower with visible white petals at the top of the inflorescence and is defined as p 1. Subsequently older flowers along the inflorescence (p0-p8). Cell wall remodeling in AZ cells, accompanied with a reduction in petal breakstrength (the force required to remove a petal from the receptacle) is initiated at p6 (red arrow). By p7 AZ cells have undergone cell separation and the floral organs have abscised. p=position b, Increase in [Ca2+]cyt in flowers expressing the cytosolic localized Aequorin-based luminescence Ca2+ sensor (Aeq) measured in relative light units (RLU) treated with 1 μM mIDA. A [Ca2+]cyt increase is observed in flowers where there is an initial weakening of the cell walls (p5-6) (black). No increase in luminescence was observed in Aeq expressing flowers of an earlier developmental stage (p3) (gray). Curves show representative measurements. Three independent experiments were performed with 4-6 replicates in each experiment.

mIDAΔN69 does not induce a [Ca2+]cyt release in Arabidopsis abscission zones (AZ)

Normalized R-GECO1 fluorescence intensities (ΔF/F) were measured from regions of interest (ROI) (outlined in red) in the floral AZs. Shown are cytosolic calcium concentration ([Ca2+]cyt) dynamics in the ROI in response to application of 1 μM mIDAΔN69 or eATP over time. Red lines at 5 minutes (min) indicates application of mIDAΔN69 peptide or application of eATP at 30 min (see also Movie 4). Representative response from 10 flowers. The increase in [Ca2+]cyt response to eATP propagates through the AZ as a single wave seen as normalized R-GECO1 fluorescence intensities (ΔF/F) shown as a heat map.

Investigation of CNGCs and RBOHs in the abscission process

a, Relative expression of CNGC1, CNGC2, CNGC4, CNGC5, CNGC6, CNGC9, CNGC12, RBOHD and RBOHF in the floral organs during the onset of abscission (Cai and lashbrook 2008). X-axis represents the developmental stages of abscission where position 12 represent flowers where the stamen and petals are of the same length, position 13 represent flowers at anthesis, position 15 represent flowers with stigma extended above the anthers. Floral organ abscission occurs at position 15. Relative expression of HAE and HSL2 added for comparison. Nomenclature for the abscission process and relative expression values taken from (Cai and Lashbrook 2008). b, No floral organ abscission phenotype is observed in the single cngc mutant plants compared to the hae hsl2 mutant which retains the floral organ indefinitely. Scale bar = 2cm, 5 weeks old plants. c, ROS production in the AZ (white arrow head) detected by using the fluorescent dye H2DCF-DA in WT and rbohd rbohf flowers at position 6 (See Supplementary Fig. 5a for positions). Scale bar = 100 µm, maximum intensity projections of z-stacks. Representative pictures from 9 flowers. d, Representative pictures of WT and rbohd rbohf inflorescences, scale bar for inflorescences = 1 cm. e, Petal break strength (pBS) measurements of WT and the rbohd rbohf mutant at position 1-6 along the inflorescence. Force required to remove petals from the receptacle represented in gram equivalent. * = significantly different from WT at the given position (p < 0.05, student t-test, two tailed).

mIDA induced expression of defense-associated marker genes is only partially dependent on the HAE and HSL2 receptors

RT-qPCR data showing transcription of FRK1, MYB51, and PEP3 in Col-0 WT and hae hsl2 seedlings exposed to 1 µM mIDA for 1 h compared to untreated seedlings (No treatment). ACTIN was used to normalize mRNA levels. Figure represent 3 biological replicates with 4 technical replicates. Statistical analyses was performed comparing samples within same gene, using two-way ANOVA and post-hoc Tukey’s test (p < 0.05).

mIDA and flg22 induced expression of pMYB51:YFP

Representative microscopic pictures of 7-days-old pMYB51:YFPN roots from seedlings transferred to liquid medium with 1 μM flg22 or 1 μM mIDA for 1, 3, 5 and 7 h using a fluorescent microscope. Control seedlings were transferred to medium with no peptide and imaged in the same time frame. Fluorescent nuclei could be observed in a similar temporal pattern in roots subjected to mIDA and flg22. Scale bar = 100 μm, single plane images using a Zeiss Axioplan2 microscope with an AxioCam HRc, 20x air objective and a YFP filter (Excitation: 500/20, Beamsplitter: FT515, Emission: 535/50), no imaging processing was performed, t = time in h. n = 3, experiment repeated 3 times.

HAE (yellow) and HSL2 (red) display very distinct repertoire of immune and growth-related interacting LRR-RKs.

HEA and HSL2 specific interacting partners determined using a sensitized high-throughput extracellular domain interaction assay (Smakowska-Luzan et al,.2018). HSL2 and HAE show distinct interacting LRR-RKs where only HSL2 was found to interact with RLK7 (red halo). * indicates receptors known to play a function in biotic and/or abiotic responses in planta based on previous published work, dark blue nodes refer to bidirectional interactions with GeoMean ≥2.5, light blue nodes-refer to bidirectional interactions with GeoMean ≤2.5, and grey nodes refer to unidirectional interactions.