Overholt, A. M. | Search bioRxiv

bioRxiv2024

ERECTA family signaling controls cell fate specification during ovule initiation in Arabidopsis.

The number of seeds produced by a plant depends on the number of ovules initiated within the carpels by a meristematic tissue, the placenta. Previous studies indicated that ERECTA-LIKE1 (ERL1) and ERL2 receptors and their extracellular ligand EPIDERMAL PATTERNING FACTOR-LIKE2 (EPFL2) promote seed density while ERECTA inhibits it. Here, we show that all three receptors and two ligands, EPFL1 and EPFL2, promote ovule initiation. After initiation, EPFL1 and EPFL2 redundantly regulate the elongation of nascent ovules and promote the growth of the funiculus. The synergy of EPFL1 and EPFL2 with CUP-SHAPED COTYLEDON boundary genes in the regulation of ovule number and shape suggests cooperation in their function. Ovule initiation starts with the specification of ovule founder cells that are separated by boundary cells. During ovule bulging, a new cell type, characterized by a high proliferative rate, forms between ovule founder and boundary cells. In the epfl1 epfl2 mutant, marker genes for ovule founder and boundary cells are expressed much more broadly. Our data indicate that ERECTA family signaling is necessary for efficient cell fate separation at the earliest stages of ovule initiation. Later, it promotes the formation of a zone of high proliferation at the base of the ovule.

plant biology↗

bioRxiv2023

An updated model of shoot apical meristem regulation by ERECTA family and CLAVATA3 signaling pathways

The shoot apical meristem (SAM) gives rise to above-ground organs. The size of the SAM is relatively constant due to the balance of stem cell replenishment versus cell recruitment into developing organs. In angiosperms, the transcription factor WUSCHEL (WUS) promotes stem cell identity in the central zone of the SAM. WUS forms a negative feedback loop with a signaling pathway activated by CLAVATA3 (CLV3). In the periphery of the SAM, the ERECTA family (ERf) receptors promote cell differentiation and constrain the expression of WUS and CLV3. Here, we show that four ligands of ERfs redundantly inhibit CLV3 and WUS expression. Transcriptome analysis confirmed that WUS and CLV3 are the main targets of ERf signaling and uncovered several new ones. Analysis of promoter reporters indicated that in the vegetative meristem, the WUS expression domain mostly overlapped with the CLV3 domain and did not shift along the apical-basal axis in clv3. A 3D mathematical model reproduced the experimentally observed CLV3 and WUS expression patterns with fewer assumptions than earlier models. Based on these findings, we propose that CLV3 regulates cellular levels of WUS expression through autocrine signaling, while ERfs regulate WUS spatial expression, preventing its encroachment into the peripheral zone. One Sentence SummaryThrough autocrine signaling, CLV3 regulates the level of WUS expression in the vegetative SAM but not its location, while ERfs regulate the WUS spatial pattern, preventing its expansion into the peripheral zone.

plant biology↗