KAR1-dormancy release in Avena fatua caryopses includes increased AfMAN gene expression and ENDO-β-MANNANASE activity in the coleorhiza and radicle

Abstract

KAR₁, at very low concentration (3x10⁻⁹ M) released dormancy in Avena fatua caryopses, which was expressed in almost complete emergence of coleorhiza (CE) and radicle (RE) just after three days of germination. The dormancy-releasing effect of KAR₁ was associated with an increased activity of ENDO-β-MANNANASE (MAN; EC 3.2.1.78) (hydrolase and transglycosylase) in coleorhiza and radicle before RE. The MAN genes, MAN1, MAN2, MAN3, MAN4, and MAN5 were for the first time identified in the genome of A. fatua. KAR₁ induced expression of AfMAN1-3 and AfMAN5 in the coleorhiza and AfMAN2 and AfMAN3 in the radicle during caryopses germination. The increase in transcripts in the coleorhiza of AfMAN1,5 after 8 h and AfMAN3,5 after 12 h germination in the presence of KAR₁ is probably responsible for the increase in MAN activity determined after 18 h before RE. KAR₁ also increased AfMAN3 expression in radicle after 12 h which probably caused the increased MAN activity after 18 h. Therefore, release of caryopses dormancy by KAR₁ involves increasing expression of MAN genes and MAN activity both in the coleorhiza and radicle, which might facilitate the passage of the radicle through the coleorhiza. The work provides the first data on the contribution of MAN, present in coleorhiza and radicle, in the dormancy release of caryopses by KAR₁.