A Peptide Pair Coordinates Regular Ovule Initiation Patterns with Seed Number and Fruit Size

Abstract

fruits is controlled by two secreted peptides, EPFL2 and EPFL9 (also known as Stomagen), and their receptors from the ERECTA (ER) family that act from the carpel wall and the placental tissue. We found that a signalling pathway controlled by EPFL9 acting from the carpel wall through the LRR-receptor kinases ER, ERL1 and ERL2 promotes fruit growth. Regular spacing of ovules depends on EPFL2 expression in the carpel wall and in the inter-ovule spaces, where it acts through ERL1 and ERL2. Loss of EPFL2 signalling results in shorter fruits and irregular spacing of ovules or even ovule twinning. The EPFL2 expression pattern between ovules is under negative-feedback regulation by auxin, which accumulates in the arising ovule primordia. We propose that the auxin-EPFL2 signalling module evolved to control the initiation and regular, equidistant spacing of ovule primordia, which serves to minimise competition between developing seeds. Together, EPFL2 and EPFL9 coordinate ovule patterning and thereby seed number with fruit growth through a set of shared receptors.Reduction of ovule number observed in er-105 seems to be an indirect consequence of the smaller fruit size and the limited availability of space. The EPFL2 pathway also affects fruit growth, but has a more pronounced impact on the patterning of ovule initial cells and 3 thus increases ovule density (Figure 6A, B).

The Boundary-Expressed EPIDERMAL PATTERNING FACTOR-LIKE2 Gene Encoding a Signaling Peptide Promotes Cotyledon Growth during Arabidopsis thaliana Embryogenesis

“…We also analyzed epfl2-2 and epfl2-3 , which are CRIPR/Cas9-induced alleles in the Col background, and they both showed similar reduction in cotyledon height (Figure 2H, I), although their phenotypes were milder compared to that of the L er allele epfl2-1 (e.g., 33.9 % and 23.0 % reduction in epfl2-2 and epfl2-3 , respectively, for embryos with 51– 100 μm axis height range). The deduced amino acid sequence produced from epfl2-2 completely lacks a mature peptide (Kawamoto et al 2020), indicating that this allele is null, similar to epfl2-1 . Therefore, the observed difference in the phenotypic severity of epfl2-1 and epfl2-2 is likely due to their difference in genetic background rather than that in allele strength.…”

“…The A. thaliana accessions L er and Col were used as the wild-type strains. The EPFL2pro::GUS reporter (Col background), transposon insertion allele epfl2-1 (L er background), and CIRSPR/Cas9-induced alleles epfl2-2 and epfl2-3 (Col background) were described previously (Kawamoto et al 2020; Tameshige et al 2016). For the analysis of DR5rev::GFP (Friml et al 2003), the epfl2-1 allele was backcrossed to Col seven times and then crossed with the reporter line of the Col background (Tameshige et al 2016).…”

Organ geometry channels reproductive cell fate in the Arabidopsis ovule primordium

“…In addition, best-fit models produced by both cell- and tissue-based simulations predicted a growth-promoting signal in a confined domain along a vertical stripe at primordium emergence. Candidate growth signals are phytohormones, peptides, and small RNAs known to affect ovule primordium growth ( Kawamoto et al, 2020 ; Pinto et al, 2019 ; Su et al, 2020 ). The domains of auxin response restricted in the L1 dome and of cytokinin signaling localized in a region basal to the SMC in Phase II primordia ( Bencivenga et al, 2012 ) also suggest a confined growth signal.…”

“…The predicted role of the primordium epidermis to accommodate – and perhaps feedback on – underlying growth constraints is particularly interesting considering the role of mechanical cues on gene regulation ( Fal et al, 2017 ; Landrein et al, 2015 ). The epidermis of the ovule primordium is also a known source of signaling cues ( Kawamoto et al, 2020 ; Pinto et al, 2019 ; Su et al, 2020 ). In addition, phytohormones act themselves on KATANIN-mediated oriented cell growth and cell division ( Luptovčiak et al, 2017a ).…”

The boundary-expressed <i>EPIDERMAL PATTERNING FACTOR-LIKE2</i> gene encoding a signaling peptide promotes cotyledon growth during <i>Arabidopsis thaliana</i> embryogenesis

“…Among these molecules, the EPIDERMAL PATTERNING FACTOR-LIKE (EPFL) family of secreted cysteine-rich proteins is involved in various developmental pathways, including epidermal cell patterning, inflorescence architecture, and lateral shoot organ patterning (Tameshige et al 2017;Torii 2012). Several studies have shown that one of the genes encoding an EPFL family member, EPFL2, is specifically expressed in the boundary domains of various shoot organs and regulates shoot meristem size, leaf and ovule positioning, and leaf margin morphogenesis (Kawamoto et al 2020;Kosentka et al 2019;Tameshige et al 2016). The boundary-specific expression of this gene has also been reported during embryogenesis (Kosentka et al 2019), in which a series of patterning and growth events occur to establish the basic body plan (Palovaara et al 2016).…”