The mutation nrpb1-A325V in the largest subunit of RNA polymerase II suppresses compromised growth of Arabidopsis plants deficient in a function of the general transcription factor IIF.

The evolutionarily conserved 12-subunit RNA polymerase II (Pol II) is a central catalytic component that drives RNA synthesis during the transcription cycle that consists of transcription initiation, elongation, and termination. A diverse set of general transcription factors, including a multifunctional TFIIF, govern Pol II selectivity, kinetic properties, and transcription coupling with posttranscriptional processes. Here, we show that TFIIF of Arabidopsis (Arabidopsis thaliana) resembles the metazoan complex that is composed of the TFIIFα and TFIIFß polypeptides. Arabidopsis has two TFIIFß subunits, of which TFIIFß1/MAN1 is essential and TFIIFß2/MAN2 is not. In the partial loss-of-function mutant allele man1-1, the winged helix domain of Arabidopsis TFIIFß1/MAN1 was dispensable for plant viability, whereas the cellular organization of the shoot and root apical meristems were abnormal. Forward genetic screening identified an epistatic interaction between the largest Pol II subunit nrpb1-A325V variant and the man1-1 mutation. The suppression of the man1-1 mutant developmental defects by a mutation in Pol II suggests a link between TFIIF functions in Arabidopsis transcription cycle and the maintenance of cellular organization in the shoot and root apical meristems.