No abstract

SWITCH deficient SUCROSE NONFERMENTING (SWI/SNF) class chromatin remodeling complexes (CRCs) use the energy derived from ATP hydrolysis to facilitate access of proteins to the genomic DNA for transcription, replication, and DNA repair. Uniquely, SWI/SNF CRCs can both slide the histone octamer along the DNA or eject it from the DNA. Given their ability to change the chromatin status quo, SWI/SNF remodelers are critical for cell fate reprogramming with pioneer and other transcription factors, for responses to environmental challenges, and for disease prevention. Recent cryo-electron microscopy and mass spectrometry approaches have uncovered different subtypes of SWI/SNF complexes with unique properties and functions. At the same time, tethering or rapid depletion and inactivation of SWI/SNF have provided novel insight into SWI/SNF requirements for enhancer activity and into balancing chromatin compaction and accessibility in concert with Polycomb complexes. Given their importance, SWI/SNF recruitment to genomic locations by transcription factors and their biochemical activity is tightly controlled. This review focuses on recent advances in our understanding of SWI/SNF CRCs in animals and plants and discusses the multiple nuclear and biological roles of SWI/SNF CRCs and how SWI/SNF activity is altered by complex subunit composition, posttranslational modifications, and the chromatin context to support proper development and response to extrinsic cues. Expected final online publication date for the Annual Review of Plant Biology, Volume 74 is May 2023. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Stem cell homeostasis by the WUSCHEL–CLAVATA (WUS-CLV) feedback loop is generally conserved across species; however, its links with other meristem regulators can be species-specific, rice being an example. We characterized the role of rice OsbZIP47 in vegetative and reproductive development. The knockdown (KD) transgenics showed meristem size abnormality and defects in developmental progression. The size of the shoot apical meristem (SAM) in 25-day OsbZIP47KD plants was increased as compared to the wild-type (WT). Inflorescence of KD plants showed reduced rachis length, number of primary branches, and spikelets. Florets had defects in the second and third whorl organs and increased organ number. OsbZIP47KD SAM and panicles had abnormal expression for CLAVATA peptide-like signaling genes, such as FON2-LIKE CLE PROTEIN1 (FCP1), FLORAL ORGAN NUMBER 2 (FON2), and hormone pathway genes, such as cytokinin (CK) ISOPENTEYLTRANSFERASE1 (OsIPT1), ISOPENTEYLTRANSFERASE 8 (OsIPT8), auxin biosynthesis OsYUCCA6, OsYUCCA7 and gibberellic acid (GA) biosynthesis genes, such as GRAIN NUMBER PER PANICLE1 (GNP1/OsGA20OX1) and SHORTENED BASAL INTERNODE (SBI/OsGA2ox4). The effects on ABBERANT PANICLE ORGANIZATION1 (APO1), OsMADS16, and DROOPING LEAF (DL) relate to the second and third whorl floret phenotypes in OsbZIP47KD. Protein interaction assays showed OsbZIP47 partnerships with RICE HOMEOBOX1 (OSH1), RICE FLORICULA/LEAFY (RFL), and OsMADS1 transcription factors. The meta-analysis of KD panicle transcriptomes in OsbZIP47KD, OsMADS1KD, and RFLKD transgenics, combined with global OSH1 binding sites divulge potential targets coregulated by OsbZIP47, OsMADS1, OSH1, and RFL. Further, we demonstrate that OsbZIP47 redox status affects its DNA binding affinity to a cis element in FCP1, a target locus. Taken together, we provide insights on OsbZIP47 roles in SAM development, inflorescence branching, and floret development.

Stem cell homeostasis by the WUS-CLV negative feedback loop is generally conserved across species; however, its links with other meristem regulators may have species-specific distinctions, rice being an example. We characterize rice OsbZIP47 for vegetative and inflorescence phenotypes in knockdown (OsbZIP47KD) transgenics and uncover its role in meristem maintenance and developmental progression. The shoot apical meristem (SAM) size in five day old OsbZIP47KD seedlings, was reduced as compared to the wild-type (WT). Whereas SAM in older twenty-five-day OsbZIP47KD plants was larger with increased size for L1 and underlying cells. We tested protein interactions of OsbZIP47 with other transcription factors and found partnerships with OsMADS1, RFL, and OSH1. Results from meta-analysis of deregulated panicle transcriptome datasets, in OsbZIP47KD, OsMADS1KD and RFLKD knockdown transgenics, and OSH1 genome-wide binding sites divulge potential targets coregulated by OsbZIP47, OsMADS1, OSH1 and RFL. Transcript analysis in OsbZIP47KD SAM and panicles showed abnormal gene expression for CLAVATA peptide-like signaling FON2-LIKE CLE PROTEIN1 (FCP1), FLORAL ORGAN NUMBER 2 (FON2), and hormone pathway: cytokinin (CK) Isopenteyltransferase2 (OsIPT2), Isopenteyltransferase8 (OsIPT8); auxin biosynthesis OsYUCCA6, OsYUCCA7; gibberellic acid (GA) biosynthesis GA20Ox1, GA20Ox4 and brassinosteriod biosynthesis CYP734A4 genes. The effects on ABBERANT PANICLE ORGANIZATION1 (APO1), OsMADS16, and DROOPING LEAF relate to second and third whorl organ phenotypes in OsbZIP47KD florets. Further, we demonstrate that OsbZIP47 redox status affects its DNA binding to cis elements in the FCP1 locus. Taken together, we provide insights on unique functional roles for OsbZIP47 in rice shoot meristem maintenance, its progression through inflorescence branching and floret development.