Sorenson, R. S.; Sieburth, L. E.

RNA decay is essential for maintenance of normal RNA abundances, however RNA abundances are regulated by two opposing processes, transcription and decay, yet how decay contributes to abundance change is poorly understood. Here, we measured rates of RNA abundance change, RNA half-lives (t1/2s), and transcription rates in stimulated Arabidopsis leaf cells. This revealed two mechanisms in which decay influenced RNA abundance changes. The biggest changes in RNA abundances resulted from t1/2 changes that reinforced transcriptional regulation (synergistic). Smaller RNA abundance changes arose from a second mechanism in which t1/2 changes opposed transcriptional regulation (oppositional). RNA decay also contributed to stimulus-induced buffering of RNA abundances. Oppositional and buffering regulation shared excessive rate changes where changes in decay rates were commensurate and opposing transcriptional changes. We call this common mechanism countercyclical regulation. Its mirroring of rate changes implies coordination between nuclear and cytoplasmic processes, and it is widespread, accounting for 90% of the RNA t1/2 regulation.