FAR-RED ELONGATED HYPOCOTYL3 activates SEPALLATA2 but inhibits CLAVATA3 to regulate meristem determinacy and maintenance in Arabidopsis

Abstract

Plant meristems are responsible for the generation of all plant tissues and organs. Here we show that the transcription factor (TF) FAR-RED ELONGATED HYPOCOTYL3 (FHY3) plays an important role in both floral meristem (FM) determinacy and shoot apical meristem maintenance in Arabidopsis, in addition to its well-known multifaceted roles in plant growth and development during the vegetative stage. Through genetic analyses, we show that WUSCHEL (WUS) and CLAVATA3 (CLV3), two central players in the establishment and maintenance of meristems, are epistatic to FHY3. Using genome-wide ChIP-seq and RNA-seq data, we identify hundreds of FHY3 target genes in flowers and find that FHY3 mainly acts as a transcriptional repressor in flower development, in contrast to its transcriptional activator role in seedlings. Binding motif-enrichment analyses indicate that FHY3 may coregulate flower development with three flowerspecific MADS-domain TFs and four basic helix-loop-helix TFs that are involved in photomorphogenesis. We further demonstrate that CLV3, SEPALLATA1 (SEP1), and SEP2 are FHY3 target genes. In shoot apical meristem, FHY3 directly represses CLV3, which consequently regulates WUS to maintain the stem cell pool. Intriguingly, CLV3 expression did not change significantly in fhy3 and phytochrome B mutants before and after light treatment, indicating that FHY3 and phytochrome B are involved in light-regulated meristem activity. In FM, FHY3 directly represses CLV3, but activates SEP2, to ultimately promote FM determinacy. Taken together, our results reveal insights into the mechanisms of meristem maintenance and determinacy, and illustrate how the roles of a single TF may vary in different organs and developmental stages. meristem maintenance | meristem determinacy | FHY3 | CLV3 | SEP2 P lant meristems are responsible for the generation of all plant tissues and organs. Unlike the shoot apical meristem (SAM), whose activity is maintained throughout the life of plants, the floral meristem (FM) is precisely programmed to terminate in a process known as FM determinacy (1). WUSCHEL (WUS) plays a central role in the establishment and maintenance of SAM, inflorescence meristem, and FM, as well as in FM determinacy (2-4). WUS is expressed in the organizing center located beneath the stem cells in the meristem to promote cell proliferation by maintaining stem cell potential (2). The WUS/CLAVATA3 (CLV3) signaling pathway maintains the stabilization of meristem size and the stem cell pool (3, 5). Consistent with WUS overactivation, clv3 mutants have an enlarged SAM and increased numbers of floral organs and whorls (5). In addition to the WUS/CLV3 loop, several other pathways are known to regulate FM determinacy (4). AGAMOUS (AG) encodes a MADS-box transcription factor (TF) and is the lynchpin of the FM determinacy network (4, 6, 7). In the null ag-1 mutant, FM determinacy is severely impaired, resulting in a flower-in-flower phenotype (6). AG inhibits WUS expression through both indirect and direct means (8, 9). A number of other gene...

Floral Organogenesis: When Knowing Your ABCs Is Not Enough

“…The transcription factor FAR-RED ELONGATED HYPOCOTYL3 (FHY3), which is involved in photomorphogenesis, was shown to control the expression of the stem cell regulator CLAVATA3 (CLV3) in the shoot apical meristem (Li et al, 2016). In floral meristems, FHY3 controls determinacy by directly repressing CLV3 and by activating the E class gene SEPALLATA2.…”

FAR-RED ELONGATED HYPOCOTYL3 promotes floral meristem determinacy in Arabidopsis

“…1A-D). 16,17 While far1-2 produced normal siliques with 2 carpels, the siliques of fhy3-68 had 2.59 § 0 .7 carpels (n D 46), indicative of a weak FM determinacy defect of fhy3-68 ( Fig. 1C and E).…”

“…16 Averysmall number of DEGs (29 up-regulated and 3 downregulated genes) were observedintheag-10sample,inlinewithitspointmutationandweak FM determinacy defects. The greater number of upregulated genes than down-regulated genes in fhy3 compared to Ler indicated that FHY3playsarepressiveroleinflowerdevelopment (Fig.3).Thisfinding was corroborated by the analysis of fhy3-68 ag-10 vs. ag-10 and fhy3-68 ag-10 vs. Ler.…”

“…The greater number of upregulated genes than down-regulated genes in fhy3 compared to Ler indicated that FHY3playsarepressiveroleinflowerdevelopment (Fig.3).Thisfinding was corroborated by the analysis of fhy3-68 ag-10 vs. ag-10 and fhy3-68 ag-10 vs. Ler. 16 Decreased numbers of both up-and downregulated genes between fhy3-68 vs. Ler and fhy3-68 vs. ag-10 (1442 to 1138 up-regulated genes and 399 to 211 down-regulated genes) indicated thatFHY3may co-regulate a group of geneswith AG (Fig. 3).…”

“…1C and E). 16 We therefore crossed ag-10 with far1-2, a null mutant, 7 to investigate the role of FAR1 in FM determinacy. The FM determinacy phenotype of far1-2 ag-10 resembled that of far1-2 and ag-10 with normal carpel numbers ( Fig.…”