Our results show transgenic and WT Petunia hybrida plant morphology, physiology, biochemical metabolism, and the regulation of genes involved in senescence. BAS1, part of C–26-hydroxylase, is an important brassinosteroid inactivating gene[26–29], which affects the content of active brassinosteroids in plants. The overexpression of plant brassinosteroids affects plant phenotype, but the mechanism of BAS1 action on plant senescence is not completely understood.
Our experimental results show that the BAS1 gene of Petunia hybrida can affect senescence signals and activity of the protective enzymes SOD, POD, and CAT in leaves. SOD, POD, and CAT activities in transgenic Petunia hybrida leaves increased by 82.74 %, 131.80 %, and 135 %, respectively, compared to WT Petunia hybrida . During plant senescence, the expression ofthe SAG12-BAS1 gene improved the activity of protective enzymes and enhanced oxygen scavenging activity in the plant. In contrast, MDA content was 46 % lower in transgenic Petunia hybrida compared to WT, which suggests that the cell membranes of transgenic Petunia hybrida were not damaged. In addition, the chlorophyll and soluble sugar content in transgenic Petunia hybrida leaves were higher than in WT plants.
Overexpression of Type A members of the Arabidopsis response regulator (ARR) gene family, including ARR4, ARR5, ARR6, ARR7, can inhibit ARR6 transcription, and stable overexpression of ARR8 in transgenic plants inhibits the cytokinin response, suggesting that type A ARR can negatively regulate the cytokinin pathway. Additional research indicates that multiple mutants of A-ARR are suppressed in response to exogenous cytokinins. ARR15 is highly cytotoxic in response to cytokinin because His-Asp phosphorylation inhibits negative feedback regulation. In the present study, expression of PHARR4 in transgenic plants was increased to 2.35 times that of WT plants, indicating that ARR4 appears to positively regulate cytokinin levels.
The cytokinin receptor histidine kinases, AHK2, AHK3, and CREI/AHK4/WOODEN LEG (WOL), bind to cytokinins and autophosphorylate. These receptor histidine kinases then transfer the phosphate group from a histidine residue, which is conserved in the kinase domain, to an aspartate residue, which is conserved in the signal receiving region. Phosphoric acid groups are transferred to cytoplasmic Arabidopsis histidine-phosphotransfer proteins (AHPs) and these AHPs subsequently enter the nucleus and transfer the phosphate groups to a series of ARR. This regulates the downstream cytokinin response and results in a series of biochemical effects that regulate plant growth and development. The experimental results show that the average expression of PHAHK is 2.41 times higher in the transgenic Petunia hybrida compared to the wild-type.
Gibberellins (GA) affect growth and developmental processes in plants, and gibberellin 2-oxidase (GA2ox) is an enzyme involved in the degradation of GA. Thus, plant overexpression of GA2ox results in reduced GA, and the associated phenotypic changes include dwarf phenotypes, pollen tube reduction, increased flowering time, and seed sterility in wheat, rice, tobacco, Paspalum notatum, and Solanum. Expression of GA2ox can reduce the height of plants and prolong flowering time. The reduction of endogenous GA3 concentration by GA2ox expression can not only cause plant dwarfing, but also change the time of seed dormancy and chlorophyll concentration. The results show that the average expression of PHGA2ox1 and PHGA2ox3 increased by 11 and 3 times, respectively, in transgenic Petunia hybrida compared to wild-type.
Auxin plays an important role in the growth and development of plants. Auxin signal transduction models demonstrate that under low concentrations of auxin, Aux/IAA inhibitors bind to the ARF transcription factor and inhibit the activity of ARF. When the concentration of auxin increases, the combination of the auxin receptor and auxin enhances the binding capacity of Aux/IAA. This results in ubiquitination of Aux/IAA, and degradation by the 26S proteasome. Subsequently, the ARF transcription factor becomes active, which activates or inhibits the expression of downstream genes, while Aux/IAA acts as a downstream gene and feedback inhibits auxin signaling pathways. This study indicated that expression of the PHARF4 gene in transgenic Petunia hybrida was down-regulated compared to wild-type Petunia hybrida plants, which suggests that the ARF transcription factor inhibits the auxin signal transduction pathway.
Some studies have shown that ERF1 can regulate the expression of ACS3, ACO, and ACO2 in plants, and thereby enhance the biosynthesis of ethylene in transgenic plants[36–39]. This suggests that transcription termination factors may play an important role in regulating plant ethylene biosynthesis[40,41]. The homeodomain-leucine Zipper (HD-Zip) is a type of transcription factor that is unique to higher plants and belongs to a class of homeodomain (HD) transcription factors . For conserved HD, the HD carboxyl terminal is tightly linked to the leucine zipper domain (LZ). Research suggests that these transcription factors mainly regulate the development of plants, including the development of vascular tissues and trichome. These factors are also involved in the regulation of external signals that regulate the growth of plants. Overexpression of these factors leads to a series of phenotypic variations such as black lobes, leaf leveling, life cycle shortening, and early flowering. Results show that PHERF gene expression was 50 % lower in transgenic Petunia hybrida compared to the wild-type. The homeodomain leucine zipper transcription factor, Petunia hybrida (PHHD-Zip), is involved in the regulation of biosynthesis of ethylene. The results showed that PHHD-Zip expression was reduced by 25 % in transgenic Petunia hybrida compared to the wild-type.