Gibberellic acid-mediated salt signaling in seed germination

Abstract

salinity delays seed germination by reducing GA biosynthesis. 7 ABA is a major plant growth hormone mediating plant responses to high salinity, suggesting that the salt effects on seed germination would depends on this growth hormone. We observed that the GA synthetic enzyme gene GA3ox1 is significantly repressed by high salinity. In particular, the salt repression of GA3ox1 is independent of ABA. The GA3ox1 transcription is efficiently repressed by high salinity even in the ABA-deficient aba3-1 mutant to a level comparable to that observed in control plants treated with high salt. These observations support that an ABA-independent salt signaling pathway is also involved in the GA regulation of seed germination.NTL8 is a membrane-bound NAC transcription factor in Arabidopsis. 8 It is unique among the NTL members in that the NTL8 transcription is induced by high salinity specifically in the cold-imbibed seed. While germination of control seeds is greatly reduced in the presence of high salt, that of the ntl8-1 mutant seeds is resistant to high salinity. In contrast, seeds of the transgenic plants overexpressing an active NTL8 form (NTL8ΔC) germinated very poorly under high salt conditions, indicating that NTL8 plays a role in the salt regulation of seed germination. However, the NTL8 transcription is unaffected by ABA, and germination of the ntl8-1 knockout mutant seeds is reduced by ABA to a degree similar to that of control seeds under the same conditions. It is therefore evident that NTL8-mediated salt signaling is independent of ABA.It is notable that NTL8-mediated salt regulation of seed germination is intimately related to GA signaling. RGL2 is one of the DELLA proteins that negatively regulate GA signals. 9 When GA biosynthesis is induced, the RGL2 protein is degraded via the ubiquitin-dependent degradation pathway, causing promotion of seed germination. 10 The Arabidopsis GA biosynthetic mutant, ga1-3, does not germinate in the absence of exogenously applied GA, indicating that GA is essential for seed germination. In contrast, the ga1-3 rgl2 double mutant seeds germinate nearly 100% even in the absence of exogenous GA application, indicating that RGL2 is a negative regulator of GA function in seed germination. 9 However, recent studies strongly support that there would be additional negative regulators other than RGL2 in GA signaling. 11,12 NTL8 is dramatically induced in the imbibed seed, and its induction is further elevated by cold treatment. However, the NTL8 induction decreases to a basal level within 24 hours after cold imbibition. This pattern is very similar to that of RGL2. Germination of the ntl8-1 mutant seeds is nearly 100% in the presence of 100 μM paclobutrazol (PAC), an inhibitor of GA synthesis. The NTL8 protein is released from the membranes through proteolytic cleavage. We found that this activation process is triggered in the PAC-treated Seed germination initiates the postembryonic development of plants, which determines successful seedling establishment and plant propagation. It is th...

A gene regulatory network controlled by the NAC transcription factor ANAC092/AtNAC2/ORE1 during salt-promoted senescence

“…Seed germination can be delayed under unfavourable environmental conditions such as high salinity (Kim and Park, 2008). It has been shown that 100 m m and 150 m m NaCl are permissive and restrictive conditions, respectively, for Arabidopsis seed germination (Saleki et al.…”

Molecular Cloning and Characterization of a Membrane Associated NAC Family Gene, SiNAC from Foxtail Millet [Setaria italica (L.) P. Beauv.]

“…Recently, Kim et al [10] indicated that 13 members of the NAC domain proteins from Arabidopsis thaliana and 6 from rice were membrane associated transcription factors. However, to the knowledge, NTM1, NTL8, and NTL11 are the only NAC membrane transcription factors whose physiological roles have been studied in detail [8,[10][11][12]. Therefore, exploring the biological role of novel NAC MTFs from other species is required for better understanding of the mechanisms governing their diverse functions.…”

NO Promotes Seed Germination and Seedling Growth Under High Salt May Depend on EIN3 Protein in Arabidopsis

“…Salinity is one of the major abiotic stresses that adversely affect crop productivity and quality ( Munns, 2002 ). It was reported that salt stress not only delayed the germination process, reduced the germination rate, but also inhibited the formation of plant seedling after germination ( Kim and Park, 2008 ; Lee et al, 2010 ). Plants have a complex and sophisticated network to antagonize the seed germination inhibition caused by salt stress and many plant hormones and signaling molecules are involved in the process ( Achard et al, 2006 ; Tanou et al, 2009 ; Mur et al, 2013 ).…”

“…Plants have a complex and sophisticated network to antagonize the seed germination inhibition caused by salt stress and many plant hormones and signaling molecules are involved in the process ( Achard et al, 2006 ; Tanou et al, 2009 ; Mur et al, 2013 ). The previous researchers proved that the small signaling molecules ABA, GA, SA, NO, and ETH were all directly involved in the regulation of seed germination inhibition or promotion under salt stress ( Gniazdowska et al, 2007 ; Kim and Park, 2008 ; Lee et al, 2010 ; Arc et al, 2013a , b ; Jiang et al, 2013 ; Lin et al, 2013a ). Ethylene was proposed to release the impaired seed germination and seedling growth through crosstalk with ABA, ROS, and NO during plant response to stress conditions ( Linkies et al, 2009 ; Asensi-Fabado et al, 2012 ; Lin et al, 2012 ; Arc et al, 2013b ).…”