Editors' ChoicePlant biology

DOG1 Controls Seed Germination

Science Signaling  02 Sep 2014:
Vol. 7, Issue 341, pp. ec238
DOI: 10.1126/scisignal.2005855

Variation in seed dormancy enables plants to adapt to different climates. Mature seeds of most angiosperms have a dry outer coating called the testa and an endosperm, including the embryonic growth zone known as the radicle-lower hypocotyl axis and an overlying cap. During germination, the testa and endosperm cap rupture, enabling the first root (radicle) to emerge. DOG1 (DELAY OF GERMINATION 1) is a protein that accumulates in a temperature-dependent manner during seed maturation. Seeds from Arabidopsis thaliana with deletion of DOG1 do not have a dormant phase but take longer to germinate. Graeber et al. found that Lepidium sativum, which is in the same family (Brassicaceae) as A. thaliana but naturally does not have seed dormancy, contained homologs of DOG1 that were expressed in seeds. Transgenic expression of A. thaliana DOG1 (AtDOG1) in L. sativum markedly delayed testa and endosperm rupture and seed germination and increased the endosperm cap’s resistance to mechanical puncture. Manipulations that weaken the endosperm cap, including exposure to the plant hormone gibberillic acid (GA), accelerated germination of seeds from L. sativum expressing AtDOG1. Likewise, reducing the temperature from 24º to 18ºC during imbibition (wetting) reduced the endosperm cap’s resistance to puncture and accelerated germination of seeds from these plants. Expression of AtDOG1 in L. sativum altered temperature-dependent changes in the expression of genes encoding proteins associated with cap weakening and GA metabolism and the relative abundances of several GA metabolites. In A. thaliana, wild-type seeds and those lacking DOG1 had differences in the temperature-dependent regulation of germination. Expression of LesaDOG1A in the AtDOG1-deficient seeds did not restore wild-type germination properties but rather enabled increased germination of seeds imbibed at the lower temperature. Thus, AtDOG1 may influence seed dormancy, at least in part, by repressing GA-mediated weakening of the endosperm cap.

K. Graeber, A. Linkies, T. Steinbrecher, K. Mummenhoff, D. Tarkowská, V. Turečková, M. Ignatz, K. Sperber, A. Voegele, H. de Jong, T. Urbanová, M. Strnad, G. Leubner-Metzger, DELAY OF GERMINATION 1 mediates a conserved coat-dormancy mechanism for the temperature- and gibberellin-dependent control of seed germination. Proc. Natl. Acad. Sci. U.S.A. 111, E3571–E3580 (2014). [Abstract] [Full Text]