The SWI/SNF (SWItch/Sucrose Non-Fermentable) chromatin remodeling complexes originally defined in yeast are important regulators of transcription in all eukaryotes. The human analogs of SWI/SNF are "BRG1- or BRM-associated factors", or BAF (SWI/SNF-A) and "Polybromo-associated BAF", which is also known as PBAF (SWI/SNF-B). SWI/SNF chromatin remodeling complexes consist of large multi-subunit complexes containing a Brm or Brg1 catalytic ATPase subunit and approximately 10 Brg/Brm associated factors (BAFs). BAF60s, which are found in most SWI/SNF complexes, are thought to bridge the gap between said complexes and transcription factors (Lorès et al., 2010). In living cells, BAF only binds to and remodels a subset of genomic locations. This selectivity of BAF genomic targeting is crucial for cell-type specification and for mediating precise responses to environmental signals (Ho et al., 2019).

In Arabidopsis, AtBAF60, represses seedling growth by modulating DNA accessibility of hypocotyl cell size regulatory genes. BAF60 binds nucleosome-free regions of multiple G box-containing genes, opposing in cis the promoting effect of the photomorphogenic and thermomorphogenic regulator Phytochrome Interacting Factor 4 (PIF4) on hypocotyl elongation. Furthermore, BAF60 expression level is regulated in response to light and daily rhythms (Jégu et al., 2017). Earlier it had been shown that the AtBAF60 subunit of the SWI/SNF chromatin-remodeling complex directly controls the formation of a gene loop at FLOWERING LOCUS C (Jégu et al., 2014). In both plant and animal innate immune responses, surveillance of pathogen infection is mediated by membrane-associated receptors and intracellular nucleotide-binding domain and leucine-rich-repeat receptors (NLRs). SWP73A, an ortholog of the mammalian switch/sucrose nonfermentable (SWI/SNF) chromatin-remodeling protein BAF60, suppresses the expression of NLRs either directly by binding to the NLR promoters or indirectly by affecting the alternative splicing of some NLRs through the suppression of cell division cycle 5 (CDC5), a key regulator of RNA splicing. Upon infection, bacteria-induced small RNAs silence SWP73A to activate a group of NLRs and trigger robust immune responses. SWP73A may function as a H3K9me2 reader to enhance transcription suppression (Huang et al., 2021).

There are approximately 29 BAF60 members in the maize genome.

Last updated June 2023 by John Gray

References:

Lorès P, Visvikis O, Luna R, Lemichez E, Gacon G. The SWI/SNF protein BAF60b is ubiquitinated through a signalling process involving Rac GTPase and the RING finger protein Unkempt. FEBS J. 2010 Mar;277(6):1453-64. doi: 10.1111/j.1742-4658.2010.07575.x. Epub 2010 Feb 8. PMID: 20148946.

Ho PJ, Lloyd SM, Bao X. Unwinding chromatin at the right places: how BAF is targeted to specific genomic locations during development. Development. 2019 Sep 30;146(19):dev178780. doi: 10.1242/dev.178780. PMID: 31570369; PMCID: PMC6803370.

Jégu T, Veluchamy A, Ramirez-Prado JS, Rizzi-Paillet C, Perez M, Lhomme A, Latrasse D, Coleno E, Vicaire S, Legras S, Jost B, Rougée M, Barneche F, Bergounioux C, Crespi M, Mahfouz MM, Hirt H, Raynaud C, Benhamed M. The Arabidopsis SWI/SNF protein BAF60 mediates seedling growth control by modulating DNA accessibility. Genome Biol. 2017 Jun 15;18(1):114. doi: 10.1186/s13059-017-1246-7. PMID: 28619072; PMCID: PMC5471679.

Jégu T, Latrasse D, Delarue M, Hirt H, Domenichini S, Ariel F, Crespi M, Bergounioux C, Raynaud C, Benhamed M. The BAF60 subunit of the SWI/SNF chromatin-remodeling complex directly controls the formation of a gene loop at FLOWERING LOCUS C in Arabidopsis. Plant Cell. 2014 Feb;26(2):538-51. doi: 10.1105/tpc.113.114454. Epub 2014 Feb 7. PMID: 24510722; PMCID: PMC3967024.

Huang CY, Rangel DS, Qin X, Bui C, Li R, Jia Z, Cui X, Jin H. The chromatin-remodeling protein BAF60/SWP73A regulates the plant immune receptor NLRs. Cell Host Microbe. 2021 Mar 10;29(3):425-434.e4. doi: 10.1016/j.chom.2021.01.005. Epub 2021 Feb 5. PMID: 33548199; PMCID: PMC7987208.