Acts as negative regulator of osmotic stress-induced gene expression (PubMed:10504578). Involved in the regulation of thermotolerance responses under heat stress. Functions as an upstream regulator of heat stress transcription factor (HSF) genes. Negatively regulates HSFA1A, HSFA1B AND HSFA1D, but positively controls the expression of HSFA1E, HSFA3, HSFA9, HSFB3, and DREB2C (PubMed:23087326). Forms a complex with CPL1 that modulates co-transcriptional processes such as mRNA capping and polyadenylation, and functions to repress stress-inducible gene expression (PubMed:23874224). Regulates pre-mRNA processing under salt stress (PubMed:24146632). Involved in primary miRNA processing and pri-miRNA biogenesis (PubMed:26227967, PubMed:26512101). Binds both intronless and intron-containing pri-miRNAs (PubMed:26227967). Acts as a regulator of biotic stress response gene expression and basal JA-mediated responses involved in defense. Acts as negative regulator of resistance to the fungal pathogen Fusarium oxysporum (PubMed:25985302). Homodimer (PubMed:24146632). Interacts with CPL1 (PubMed:23874224, PubMed:24146632, PubMed:24303021, PubMed:26512101). Interacts with RS40 and RS41 (PubMed:24146632). Interacts with DRB1/HYL1 and SE (PubMed:26227967). Interacts with CPL2 (PubMed:26512101). Localizes predominantly in nuclear speckles. A number of isoforms are produced. According to EST sequences. Expressed in roots, cotyledons, leaves, flowers and siliques. Transiently down-regulated by heat stress (PubMed:23087326). Down-regulated by salt stress, osmotic shock, treatment with lithium or abscisic acid (ABA), and low or high pH (PubMed:23874224). No visible phenotype under normal growth conditions (PubMed:23087326, PubMed:23874224, PubMed:24146632, PubMed:25985302). Mutant seedlings show increased tolerance to heat stress (PubMed:23087326, PubMed:25985302). Mutant seedlings show increased sensitivity to salt stress and abscisic acid (ABA) (PubMed:24146632). Mutant plants exhibit increased resistance to the fungal pathogen Fusarium oxysporum (PubMed:25985302).