| Tomato?Solanum lycopersicum?is one of the most common fruits and vegetables,and the best model for the development and maturation of fleshy fruit plants.Fruit ripening involves obvious complex biochemical and physiological changes,such as pigment accumulation for bright colouring,cell wall degradation for fruit softening and accumulation of volatiles for aromas.The SlMADS-RIN gene was the first factor to be found which can regulate fruit ripening.Recently,more and more researches revealed that the MADS-box transcriptional factors in plants not only regulate fruit ripening,but also regulate the development of floral organs identity and flowering,and play an important role in abiotic stress response.According to previous studies,four MADS-box genes SlMBP8,SlMBP15,FUL1?also known as TDR4?and FUL2?also known as Sl MBP7?were selected and studied by transgenic technology and yeast two-hybrid assay.The main results of this study are as following:Real-time quantitative PCR analysis showed that SlMBP8-RNAi accelerates fruit ripening,indicating that SlMBP8 gene may be involved in regulation of fruit ripening.In order to further explore the possible functions of SlMBP8 gene in fruit ripening,RNAi technology was used to silence SlMBP8 gene in tomato,and the transgenic fruit showed shorter fruit ripening time,higher ethylene synthesis and carotenoid accumulation.qRT-PCR analysis showed that the expression of ethylene synthesis and ripening-related genes in transgenic fruits was significantly up-regulated.These results indicated that SlMBP8 is involved in the regulation of tomato fruit ripening as a negative regulator.In addition,we found that the expression of SlMBP8 gene was induced by ACC,and the transgenic lines were more sensitive to ACC.The yeast two-hybrid assay indicated that SlMBP8 could interact with SlMADS-RIN.Additionally,the fruits of transgenic plants displayed faster water lose and decreased storability compared to wild type,which was due to the significantly induced expressions of the cell wall metabolism genes.These results suggest that SlMBP8 plays an important role in fruit ripening and softening.In addition,the expression of SlMBP8 gene was significantly induced by salt stress and dehydration stress,which has been confirmed to play important roles in stress response,indicating that SlMBP8 gene may function in response to abiotic stress.To confirm this,we compared the effects of salt stress and drought stress on transgenic plants and wild-type.The results showed that the root and stoot growth of transgenic plants were less inhibited by salt stress compared with the control plants.The chlorophyll content of transgenic leaves was higher than that of the control,indicating that transgenic plants became more tolerant to salt stress at post-germination stage.In addition,transgenic plants also showed strong tolerance to salt stress and drought stress tolerance in soil.In these two stress treatments,the expression of stress-related genes in SlMBP8-RNAi transgenic plants was up-regulated.These results indicated that SlMBP8protein functions as a stress-responsive transcription factor in negative modulation of abiotic stress tolerance.In summary,SlMBP8 gene can not only participate in the regulation of tomato fruit ripening process,but also plays an important role in tomato abiotic stress response.SlMBP15,whose expression level was increased during the process of fruit ripening,is highly homologous to gene SlMBP8.In this study,the RNAi expression vector of this gene was constructed and transformed into tomato plants AC++.The results showed that longer ripening time was observed in the transgenic fruits.qRT-PCR results showed that some of the ethylene synthesis and ethylene-responsive genes were significantly down-regulated in transgenic fruits.In transgenic fruits,there was only 80%ethylene was produced compared to wild-type,suggesting that silencing of SlMBP15 gene inhibits the ethylene synthesis,then inhibits the fruit ripening process.The yeast two-hybrid assay indicated that SlMBP15 could interact with SlMADS-RIN.These results suggest that SlMBP15 may play an important role in fruit ripening through interacting with SlMADS-RIN.In addition,we found that suppressed expression of SlMBP15 retarded plant high growth.The height of 30-days-old transgenic seedlings was only about 50%of the wild type in greenhouse.And we found that the color of the transgenic leaves was deeper green than the wild type.qRT-PCR analysis showed that the expression levels of gibberellin synthesis and gibberellin-response genes were significantly down-regulated in transgenic lines,while the expression of chlorophyll-related genes was not different from that of wild type.The accumulation of gibberellin in transgenic lines was significantly reduced.The above results indicated that suppressed expression of SlMBP15 retarded plant high growth,leading to plant dwarfing.Tomato contain two genes,FUL1?also known as TDR4?and FUL2?also known as SlMBP7?,which are highly homologous to Arabidopsis MADS-box transcription factor gene FRUITFULL?FUL?.Both genes are highly expressed in the process of fruit ripening.In order to understand the function of FUL1 and FUL2 in tomato,we constructed single and double FUL1 and FUL2 RNAi expression vectors.Single FUL1and FUL2 RNAi lines only showed slight changes in fruit pigmentation,and we inadvertently obtained the double FUL1 and FUL2 RNAi lines exhibited an orange-ripe fruit phenotype due to highly reduced lycopene levels,indicating that FUL1 and FUL2have a redundant function in fruit ripening.In contrast with previously identified ripening regulators,FUL1 and FUL2 do not regulate ethylene biosynthesis but influence ripening in an ethylene-independent manner.In this study,four MADS-box genes:SlMBP8?SlMBP15?FUL1 and FUL2 were identified from tomato,and their functions in fruit ripening,plant dwarfing and abiotic stress response were explored,which provided a set of significant data and important clues for elucidating the functions of Sl MBP8?SlMBP15?FUL1 and FUL2 genes in tomato. |
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