The Required for Cell Differentiation 1 (RCD1) protein was initially defined to be essential for sex differentiation during nitrogen starvation in yeast. It encodes a 283 amino acid protein with a conserved motif (PF04078, COG5209) (Okazaki et al., 1998). RCD1-like proteins have been identified in all branches of eukaryotes, suggesting an evolutionarily conserved sexual differentiation mechanism. In yeast RCD1 is required for nitrogen starvation-invoked, but not carbon starvation-invoked, induction of Ste11+, which in turn encodes a transcription factor with an HMG box that activates a set of genes required for conjugation and meiosis (Willer et al., 1995). RCD1 is part of the CARBON CATABOLITE REPRESSION 4-NEGATIVE ON TATA-LESS (CCR4-NOT) complex which functions as a major player in mRNA metabolism in eukaryotes (Schwenk et al., 2021). The CCR4-NOT complex is the main evolutionary conserved deadenylase complex in eukaryotes, and its function in mRNA deadenylation is essential during germline specification in animals.

In plants RCD1-like is referred to as CCR4-NOT transcription complex subunit 9 and is encoded by several paralogs in Arabidopsis (Not9a:AT5G12980, Not9b:AT3G20800, Not9c:AT2G32550), (Arae et al., 2019). Note that the Arabidopsis RADICAL-INDUCED CELL DEATH1 (RCD1) gene encodes a poly(ADP-ribose)-binding protein and is not a member of the RCD-like transcription factor family.  The CCR4-NOT complex has been studied in Arabidopsis. Disruption of the AtNOT1 gene, which encodes the scaffold protein of the CCR4-NOT complex, showed abnormal seed set.  not1 embryo sacs showed delayed development and defects in embryogenesis. not1 pollen grains exhibited abnormal male germ unit configurations and failed to germinate (Pereira et al., 2020). NOT9B, an Arabidopsis homologue of human CNOT9, is a component of the CCR4-NOT complex, and acts as negative regulator of phyA-specific light signaling when bound to NOT1, the scaffold protein of the complex. Light-activated phyA interacts with and displaces NOT9B from NOT1, suggesting a potential mechanism for light signaling through CCR4-NOT.

In maize there are 2 RCD1-like genes but they have not been studied to date. However, the maize thick aleurone1 gene encodes a NOT1 Subunit of the CCR4-NOT Complex and regulates cell patterning in the endosperm (Wu et al., 2020).

Last updated June 2023 by John Gray

References:

Okazaki N, Okazaki K, Watanabe Y, Kato-Hayashi M, Yamamoto M, Okayama H. Novel factor highly conserved among eukaryotes controls sexual development in fission yeast. Mol Cell Biol. 1998 Feb;18(2):887-95. doi: 10.1128/MCB.18.2.887. PMID: 9447985; PMCID: PMC108800.

Willer M, Hoffmann L, Styrkársdóttir U, Egel R, Davey J, Nielsen O. Two-step activation of meiosis by the mat1 locus in Schizosaccharomyces pombe. Mol Cell Biol. 1995 Sep;15(9):4964-70. doi: 10.1128/MCB.15.9.4964. PMID: 7651414; PMCID: PMC230743.

Pereira PA, Boavida LC, Santos MR, Becker JD. AtNOT1 is required for gametophyte development in Arabidopsis. Plant J. 2020 Aug;103(4):1289-1303. doi: 10.1111/tpj.14801. Epub 2020 Jul 3. PMID: 32369648.

Wu H, Gontarek BC, Yi G, Beall BD, Neelakandan AK, Adhikari B, Chen R, McCarty DR, Severin AJ, Becraft PW. The thick aleurone1 Gene Encodes a NOT1 Subunit of the CCR4-NOT Complex and Regulates Cell Patterning in Endosperm. Plant Physiol. 2020 Oct;184(2):960-972. doi: 10.1104/pp.20.00703. Epub 2020 Jul 31. PMID: 32737073; PMCID: PMC7536710.

Schwenk P, Sheerin DJ, Ponnu J, Staudt AM, Lesch KL, Lichtenberg E, Medzihradszky KF, Hoecker U, Klement E, Viczián A, Hiltbrunner A. Uncovering a novel function of the CCR4-NOT complex in phytochrome A-mediated light signalling in plants. Elife. 2021 Mar 30;10:e63697. doi: 10.7554/eLife.63697. PMID: 33783355; PMCID: PMC8009681.

Arae T, Morita K, Imahori R, Suzuki Y, Yasuda S, Sato T, Yamaguchi J, Chiba Y. Identification of Arabidopsis CCR4-NOT Complexes with Pumilio RNA-Binding Proteins, APUM5 and APUM2. Plant Cell Physiol. 2019 Sep 1;60(9):2015-2025. doi: 10.1093/pcp/pcz089. PMID: 31093672.