FON2;FON4

Gene Details

MSU gene ID: LOC_Os11g38270
RAPdb gene ID: Os11g0595400
Gene Symbol: FON2 FON4 TG1
Genome: MSU7 , IRGSP-1.0
Species: Oryza sativa

Functional Descriptions

Unlike FON2, which regulates the maintenance of flower and inflorescence meristems, FCP1 appears to regulate the maintenance of the vegetative SAM and RAM.
Likely due to enlarged SAMs, FON4 mutants produced thick culms (stems) and increased numbers of both primary rachis branches and floral organs.
In rice (Oryza sativa), FLORAL ORGAN NUMBER2 (FON2), closely related to CLV3, is involved as a signaling molecule in a similar pathway to negatively regulate stem cell proliferation in the floral meristem (FM).
FON2 SPARE1 redundantly regulates floral meristem maintenance with FLORAL ORGAN NUMBER2 in rice.
Exogenous application of the peptides FON4p and CLV3p corresponding to the CLV3/ESR-related (CLE) motifs of FON4 and CLV3, respectively, resulted in termination of SAMs in rice, and treatment with CLV3p caused consumption of both rice and Arabidopsis root meristems, suggesting that the CLV pathway in limiting meristem size is conserved in both rice and Arabidopsis.
However, exogenous FON4p did not have an obvious effect on limiting both rice and Arabidopsis root meristems, suggesting that the CLE motifs of Arabidopsis CLV3 and FON4 are potentially functionally divergent.
The FON4 mutants showed abnormal enlargement of the embryonic and vegetative shoot apical meristems (SAMs) and the inflorescence and floral meristems.
To elucidate the genetic mechanism that regulates meristem maintenance in monocots, here we have examined the function of the gene FLORAL ORGAN NUMBER2 (FON2) in Oryza sativa (rice).
To understand the molecular mechanism regulating meristem development in the monocot rice (Oryza sativa), we describe here the isolation and characterization of three floral organ number4 (FON4) alleles and the cloning of the FON4 gene.
Constitutive expression of FON2 also causes premature termination of the shoot apical meristem in Arabidopsis, a phenotype similar to that caused by constitutive expression of CLV3.
Constitutive expression of FON2 causes a reduction in the number of floral organs and flowers, suggesting that both the flower and inflorescence meristems are reduced in size.
FON4 transcripts mainly accumulated in the small group of cells at the apex of the SAMs, whereas the rice ortholog of CLV1 (FON1) is expressed throughout the SAMs, suggesting that the putative FON4 ligand might be sequestered as a possible mechanism for rice meristem regulation.
Mutations in FON2 cause enlargement of the floral meristem, resulting in an increase in the number of floral organs, although the vegetative and inflorescence meristems are largely normal.
Genetic analysis revealed that FOS1 does not need FON1, the putative receptor of FON2, for its action, suggesting that FOS1 and FON2 may function in meristem maintenance as signaling molecules in independent pathways.
Here, we report that two proteins closely related to CLAVATA3, FLORAL ORGAN NUMBER2 (FON2) and FON2-LIKE CLE PROTEIN1 (FCP1/Os CLE402), have functionally diversified to regulate the different types of meristem in rice (Oryza sativa).
FON2 transcripts are localized at the apical region in all meristems in the aerial parts of rice plants, showing an expression pattern similar to that of Arabidopsis CLV3.
Together with our previous study of FON1, these results clearly indicate that the FON1-FON2 system in rice corresponds to the CLV signaling system in Arabidopsis and suggest that the negative regulation of stem cell identity by these systems may be principally conserved in a wide range of plants within the Angiosperms.
In addition, we propose a model of the genetic regulation of meristem maintenance in rice that includes an alternative pathway independent of FON2-FON1.
The mapping results showed that TG1 is allelic to FLORAL ORGAN NUMBER2 (FON2)/FLORAL ORGAN NUMBER4 (FON4), a flower organ number gene located at 88.
The novel TG1 gene allele was introgressed into the cytoplasmic male sterility (CMS) line Zhejing 22A, giving rise to a new CMS line Zhejing 22-TG1A.
The results implied great potentials for the TG1 gene in hybrid rice breeding.
Disruption of OsMADS3 in the FON2 mutant by CRISPR-Cas9 technology caused a flower phenotype similar to that of 2B-424, confirming that the gene responsible for enhancement of FON2 was OsMADS3.
Morphological analysis showed that the FON2 and osmads3 mutations synergistically affected pistil development and FM determinacy.
In FON2 mutants, the numbers of floral organs are increased due to an enlargement of the FM.
To identify new factors regulating meristem maintenance in rice, we performed a genetic screening of mutants that enhanced the FON2 mutation, and found a mutant line (2B-424) in which pistil number was dramatically increased.
FON4 prevents the multi-floret spikelet in rice.
By contrast, the stem cell region and TAB1 expression domain were expanded in FON2, and FON2 overexpression inhibited axillary meristem formation.
These results indicate that TAB1 is required to maintain stem cells during axillary meristem development, whereas FON2 negatively regulates stem cell fate by restricting TAB1 expression.
Here, we report the genetic interactions between FON4 and floral homeotic genes OsMADS15 (an A-class gene), OsMADS16 (also called SUPERWOMAN1, SPW1, a B-class gene), OsMADS3 and OsMADS58 (C-class genes), OsMADS13 (a D-class gene), and OsMADS1 (an E-class gene) during flower development.
This work reveals how the meristem maintenance gene FON4 genetically interacts with C, D, and E floral homeotic genes in specifying FM activity in monocot rice.

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