Arabidopsis thaliana Raf22 protein kinase maintains growth capacity during postgerminative growth arrest under stress

When seeds are exposed to drought and salinity during germination, newly germinated embryos stop growth and enter a quiescent state called postgerminative growth (PGG) arrest. PGG arrest protects embryos from the stress, but it is not known how PGG is restored from the arrest when stress is eased. In this study, we show that under stress- or abscisic acid-induced PGG arrest conditions, Arabidopsis thaliana Raf-type protein kinase 22 (AtRaf22) overexpression accelerated photoautotrophic seedling establishment, whereas atraf22 knockout mutations enhanced the arrest. Furthermore, when the stress intensity was reduced subsequently, AtRaf22 overexpression plants resumed growth and accomplished photoautotrophic transition much faster than the knockout or wild-type plants. These results suggest that AtRaf22 activity is important for maintaining growth capacity during stress-induced PGG arrest, which is most likely critical for competitive growth when the stress subsides and plants resume growth. Such a factor has not been reported before.