Background Transcription factor GT-3b binds to the GT-1 element in the promoter of Sadenosylmethionine synthase (SAMs) gene, the key gene of spermidine (Spd) biosynthesis, to regulate its expression, thereby increasing the salt tolerance of cucumber plants. Furthermore, exogenous Spd increases the transcript level and protein abundance of SAMs, which promotes the accumulation of endogenous polyamine. However, whether Spd regulation of SAMs depending on GT-3b is largely unknown. Here, we investigated the potential mechanism of Spd in regulating of GT-3b in cucumber seedlings under salt stress. Results Exogenous Spd significantly increased the tolerance to salt stress in cucumber, while its effects were compromised when application of methylglyoxal bis-guanylhydrazone (MGBG), an inhibitor of Spd biosynthesis. GT-3b was significantly induced by Spd under salt stress. The promoter sequence of GT-3b was predicted that there contained cis-acting regulatory elements response to phytohormones, such as gibberellin (GA), salicylic acid (SA) and methyl jasmonate (MeJA). Foliar spray of GA 3 , SA and MeJA could induce the expression of GT-3b. Interestingly, exogenous Spd dramatically induced the expression of genes related to GA biosynthesis, increased the activity of gibberellin oxidase, and promoted the accumulation of GA 3 , but decreased in MGBG-treated plants. Furthermore, application of GA 3 increased the expression of GT-3b and salt tolerance, while blocked when treatment with paclobutrazol (PAZ), the GA biosynthesis inhibitor. In addition, Spd-induced salt tolerance was compromised in PAZ-treated plants. Conclusions Our results suggested that GA mediated Spd-induced salt tolerance and the expression of GT-3b in cucumber. These results provide new perspective for our understanding the molecular mechanism of Spd in regulation of salt tolerance in plants.
Grafting is one of the key agronomic measures to enhance the tolerance to environmental stresses in horticultural plants, but the specific molecular regulation mechanism in this tolerance largely remains unclear. Here, we found that cucumber grafted onto figleaf gourd rootstock increased cold tolerance through abscisic acid (ABA) activating WRKY41/WRKY46-miR396b-5p-TPR (tetratricopeptide repeat-like superfamily protein) module. Cucumber seedlings grafted onto figleaf gourd increased cold tolerance and induced the expression of miR396b-5p. Furthermore, overexpression of cucumber miR396b-5p in Arabidopsis improved cold tolerance. 5’ RNA ligase-mediated rapid amplification of cDNA ends (5’ RLM-RACE) and transient transformation experiments demonstrated that TPR was the target gene of miR396b-5p, while TPR overexpression plants were hypersensitive to cold stress. The yeast one-hybrid and dual-luciferase assays showed that both WRKY41 and WRKY46 bound to MIR396b-5p promoter to induce its expression. Furthermore, cold stress enhanced the content of ABA in the roots and leaves of figleaf gourd grafted cucumber seedlings. Exogenous application of ABA induced the expression of WRKY41 and WRKY46, and cold tolerance of grafted cucumber seedlings. However, figleaf gourd rootstock-induced cold tolerance was compromised when plants were pretreated with ABA biosynthesis inhibitor. Thus, ABA mediated figleaf gourd grafting-induced cold tolerance of cucumber seedlings through activating the WRKY41/WRKY46-miR396b-5p-TPR module.
Background Transcription factor GT-3b binds to the GT-1 element in the promoter of S -adenosylmethionine synthase ( SAMs ) gene, the key gene of spermidine (Spd) biosynthesis, to regulate its expression, thereby increasing the salt tolerance of cucumber plants. Furthermore, exogenous Spd increases the transcript level and protein abundance of SAMs, which promotes the accumulation of endogenous polyamine. However, whether Spd regulation of SAMs depending on GT-3b is largely unknown. Here, we investigated the potential mechanism of Spd in regulating of GT-3b in cucumber seedlings under salt stress.Results Exogenous Spd significantly increased the tolerance to salt stress in cucumber, while its effects were compromised when application of methylglyoxal bis-guanylhydrazone (MGBG), an inhibitor of Spd biosynthesis. GT-3b was significantly induced by Spd under salt stress. The promoter sequence of GT-3b was predicted that there contained cis-acting regulatory elements response to phytohormones, such as gibberellin (GA), salicylic acid (SA) and methyl jasmonate (MeJA). Foliar spray of GA 3 , SA and MeJA could induce the expression of GT-3b . Interestingly, exogenous Spd dramatically induced the expression of genes related to GA biosynthesis, increased the activity of gibberellin oxidase, and promoted the accumulation of GA 3 , but decreased in MGBG-treated plants. Furthermore, application of GA 3 increased the expression of GT-3b and salt tolerance, while blocked when treatment with paclobutrazol (PAZ), the GA biosynthesis inhibitor. In addition, Spd-induced salt tolerance was compromised in PAZ-treated plants.Conclusions Our results suggested that GA mediated Spd-induced salt tolerance and the expression of GT-3b in cucumber. These results provide new perspective for our understanding the molecular mechanism of Spd in regulation of salt tolerance in plants.
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