Expansin gene expression in Datura ferox L. seeds is regulated by the low-fluence response, but not by the high-irradiance response, of phytochromes

Abstract

Expansins are a multi-gene family of proteins involved in changes in cell wall properties. In seeds where the embryo is completely surrounded by the endosperm, dormancy breakage requires weakening of the micropylar endosperm, increased embryo growth potential or both. Cell wall alterations are fundamental components of these processes, and expansins are thought to participate in them. Here, we explore the possible involvement of expansins in the control of germination by phytochrome in Datura ferox L. seeds. Based on the conserved sequences of known expansin genes, corresponding primers were designed to investigate the expression of expansin mRNAs by reverse transcriptase polymerase chain reaction (RT-PCR). One expansin mRNA was detected in micropylar endosperm of D. ferox, while two mRNAs were present in the embryo prior to radicle emergence. Expansin transcript content is promoted by red (R) light, both in the micropylar endosperm and the embryo; these effects of R are far-red light (FR) reversible, displaying a typical low-fluence response (LFR) in a way fully consistent with the photocontrol of germination. On the other hand, when the promotion of germination by the LFR is antagonized by exposing the seeds to continuous FR through a high-irradiance response (HIR) or by ABA, the inhibitory treatments do not affect expansin mRNA abundance. The results support the participation of expansins in the promotion of germination by LFR of phytochromes, and suggest that inhibition of germination by HIR or ABA does not include a reduction in the transcription of expansin genes.