Plant BCL-DOMAIN HOMOLOG proteins play a conserved role in SWI/SNF complex stability. Plant BCL-DOMAIN HOMOLOG proteins play a conserved role in SWI/SNF complex stability

The SWItch/Sucrose Non-Fermenting (SWI/SNF) complexes are evolutionarily conserved, ATP-dependent chromatin remodelers crucial for multiple nuclear functions in eukaryotes. Recently, plant BCL-Domain Homolog (BDH) proteins were identified as shared subunits of all plant SWI/SNF complexes, significantly impacting chromatin accessibility and various developmental processes in Arabidopsis. In this study, we performed a comprehensive characterization of bdh mutants, revealing a previously overlooked impact on hypocotyl cell elongation. Through detailed analysis of BDH domains, we identified a plant-specific N-terminal domain that facilitates the interaction between BDH and the rest of the complex. Additionally, we uncovered the critical role of the BDH β-hairpin domain, which is phylogenetically related to metazoan BCL7 SWI/SNF subunits. While phylogenetic analyses did not identify BDH/BCL7 orthologs in fungi, structure prediction modeling demonstrated strong similarities between the SWI/SNF catalytic modules of plants, animals, and fungi, and revealed the yeast Rtt102 protein as a structural homolog of BDH and BCL7. This finding is supported by the ability of Rtt102 to interact with the Arabidopsis catalytic module subunit ARP7 and partially rescue the bdh mutant phenotypes. Further experiments revealed that BDH promotes the stability of the ARP4-ARP7 heterodimer, leading to the partial destabilization of ARP4 in the SWI/SNF complexes. In summary, our study unveils the molecular function of BDH proteins in plant SWI/SNF complexes and suggests that β-hairpin-containing proteins are evolutionarily conserved subunits crucial for ARP heterodimer stability and SWI/SNF activity across eukaryotes. Overall design: We compared the expression profiles of wild type and bdh hypocotyls to investigate the molecular basis of the phenotypes that these mutants show when grown in darkness

开关/蔗糖非发酵（SWI/SNF）复合物是一类进化上保守的ATP依赖型染色质重塑复合物，对真核生物的多种核功能发挥关键调控作用。近期研究将植物BCL结构域同源（BCL-Domain Homolog, BDH）蛋白鉴定为所有植物SWI/SNF复合物的共有亚基，该蛋白可显著影响拟南芥（Arabidopsis）的染色质可及性与多种发育过程。本研究对bdh突变体开展了全面的功能表征，揭示了此前未被关注的其对下胚轴（hypocotyl）细胞伸长的调控作用。通过对BDH结构域的详细分析，我们鉴定出一个植物特异性的N端结构域，该结构域可介导BDH与复合物其余组分的相互作用。此外，我们还揭示了BDH β发夹（β-hairpin）结构域的关键功能，该结构域在系统发育上与后生动物BCL7 SWI/SNF亚基具有同源相关性。尽管系统发育分析未在真菌中发现BDH/BCL7的同源基因，但结构预测建模结果显示，植物、动物与真菌的SWI/SNF催化模块具有高度相似性，并鉴定出酵母Rtt102蛋白为BDH与BCL7的结构同源物。Rtt102能够与拟南芥催化模块亚基ARP7结合，并可部分恢复bdh突变体的表型，这一实验结果佐证了上述发现。后续实验表明，BDH可增强ARP4-ARP7异二聚体的稳定性，进而导致SWI/SNF复合物中ARP4蛋白的部分不稳定。综上，本研究阐明了BDH蛋白在植物SWI/SNF复合物中的分子功能，并提出：含β发夹结构的蛋白是一类进化上保守的亚基，对真核生物ARP异二聚体稳定性及SWI/SNF活性至关重要。实验设计：本研究通过比较野生型与bdh突变体下胚轴的基因表达谱，以解析这些突变体在黑暗条件下生长时所呈现表型的分子基础。