Inhibition of the gene expression for granule-bound starch synthase I by RNA interference in sweet potato plants

Granule-bound starch synthase I (GBSSI) is one of the key enzymes catalyzing the formation of amylose, a linear α(1,4)D-glucan polymer, from ADP-glucose. Amylose-free transgenic sweet potato plants were produced by inhibiting sweet potato GBSSI gene expression through RNA interference. The gene construct consisting of an inverted repeat of the first exon separated by intron 1 of GBSSI driven by the CaMV 35S promoter was integrated into the sweet potato genome by Agrobacterium tumefaciens-mediated transformation. In over 70% of the regenerated transgenic plants, the expression of GBSSI was inactivated giving rise to storage roots containing amylopectin but not amylose. Electrophoresis analysis failed to detect the GBSSI protein, suggesting that gene silencing of the GBSSI gene had occurred. These results clearly demonstrate that amylose synthesis is completely inhibited in storage roots of sweet potato plants by the constitutive production of the double-stranded RNA of GBSSI fragments. We conclude that RNA interference is an effective method for inhibiting gene expression in the starch metabolic pathway.     

Wound-response regulation of the sweet potato sporamin gene promoter region

Sporamin, a tuberous storage protein of sweet potato, was systemically expressed in leaves and stems by wound stimulation. In an effort to demonstrate the regulatory mechanism of wound response on the sporamin gene, a 1.25 kb sporamin promoter was isolated for studying the wound-induced signal transduction. Two wound response-like elements, a G box-like element and a GCC core-like sequence were found in this promoter. A construct containing the sporamin promoter fused to a -glucuronidase (GUS) gene was transferred into tobacco plants by Agrobacterium-mediated transformation. The wound-induced high level of GUS activity was observed in stems and leaves of transgenic tobacco, but not in roots. This expression pattern was similar to that of the sporamin gene in sweet potatoes. Exogenous application of methyl jasmonate (MeJA) activated the sporamin promoter in leaves and stems of sweet potato and transgenic tobacco plants. A competitive inhibitor of ethylene (2,5-norbornadiene; NBD) down-regulated the effect of MeJA on sporamin gene expression. In contrast, salicylic acid (SA), an inhibitor of the octadecanoid pathway, strongly suppressed the sporamin promoter function that was stimulated by wound and MeJA treatments. In conclusion, wound-response expression of the sporamin gene in aerial parts of plants is regulated by the octadecanoid signal pathway.     

Sugar-Dependent Expression of the CHS-A Gene for Chalcone Synthase from Petunia in Transgenic Arabidopsis

Transgenic Arabidopsis thaliana plants were constructed by introduction of a fusion of the gene for β-glucuronidase (GUS) to the CHS-A gene, which is one of the two genes for chalcone synthase that are actively expressed in the floral organs of petunia. The expression of the fusion gene CHS-A::GUS was low in transgenic Arabidopsis plantlets, but it was enhanced when plantlets or detached leaves were transferred to a medium that contained 0.3 molar sucrose, glucose, or fructose. No enhancement was observed when plantlets were transferred to a medium that contained 0.3 molar mannitol. Measurements of cellular levels of sugars revealed a tight linkage between the level of expression of the CHS-A::GUS gene and the level of accumulation of exogenously supplied sugars, in particular sucrose. The parallelism between the organ-specific accumulation of sugar and the organ-specific expression of the CHS-A::GUS gene was also observed in petunia and A. thaliana plants grown under normal conditions in soil. The consensus sequences for sugar responses, such as boxes II and III in members of the family of sporamin genes from the sweet potato, were found in the promoter region of the CHS-A gene that was used for fusion to the GUS gene. It is suggested that the expression of the CHS-A gene is regulated by sugars, as is the expression of other sugar-responsive genes, such as the genes for sporamin. A putative common mechanism for the control of expression of “sugar-related” genes, including the CHS-A gene, is discussed.     

A sucrose non‐fermenting‐1‐related protein kinase‐1 gene,IbSnRK1, improves starch content,composition, granule size,degree of crystallinity and gelatinization in transgenic sweet potato

Sucrose non‐fermenting‐1‐related protein kinase‐1 (SnRK1) is an essential energy‐sensing regulator and plays a key role in the global control of carbohydrate metabolism. The SnRK1 gene has been found to increase starch accumulation in several plant species. However, its roles in improving starch quality have not been reported to date. In this study, we found that the IbSnRK1 gene was highly expressed in the storage roots of sweet potato and strongly induced by exogenous sucrose. Its expression followed the circandian rhythm. Its overexpression not only increased starch content, but also decreased proportion of amylose, enlarged granule size and improved degree of crystallinity and gelatinization in transgenic sweet potato, which revealed, for the first time, the important roles of SnRK1 in improving starch quality of plants. The genes involved in starch biosynthesis pathway were systematically up‐regulated, and the content of ADP‐glucose as an important precursor for starch biosynthesis and the activities of key enzymes were significantly increased in transgenic sweet potato. These findings indicate that IbSnRK1 improves starch content and quality through systematical up‐regulation of the genes and the increase in key enzyme activities involved in starch biosynthesis pathway in transgenic sweet potato. This gene has the potential to improve starch content and quality in sweet potato and other plants.     

水稻胁迫相关基因OsPM1启动子的克隆与分析

依据NCBI数据库OsPM1的序列信息,采用PCR技术扩增获取OsPM1的2 100bp的启动子序列。利用PLACE预测启动子的顺式作用元件分析表明,启动子内含有大量与胁迫相关的顺式作用元件,主要有ABA响应相关元件、脱水响应元件、低温响应元件、热激响应元件和转录因子结合元件。构建OsPM1的启动子和GUS基因融合表达载体,转入拟南芥。组织化学染色分析结果显示,非生物胁迫处理前,幼苗中GUS基因表达水平很低;干旱、低温、高盐等胁迫处理后,GUS基因表达量显著升高。研究表明,OsPM1的启动子能够显著提高在干旱、高盐和低温处理后下游基因的表达水平。     

厚藤脱水素基因IpDHN启动子IpDHN-Pro的克隆和调控转录活性分析

为了解厚藤(Ipomoea pes-caprae)脱水素基因IpDHN (GenBank登录号:KX426069)启动子的转录活性和对非生物胁迫和植物激素ABA的响应,通过染色体步移法克隆了IpDHN的上游启动子序列IpDHN-Pro,长度为974 bp。构建IpDHN-Pro调控下GUS转基因载体,转化拟南芥(Arabidopsis thaliana)植株获得IpDHN-Pro::GUS转基因植株并进行GUS染色,验证IpDHN-Pro启动转录活性以及在氯化钠、甘露醇、ABA处理后拟南芥GUS基因表达变化。结果表明,扩增获得的IpDHN-Pro序列包含多个顺式作用元件,包括1个ABRE、3个Myb转录因子结合位点、富含TC的重复序列以及Skn-1基序等。转基因拟南芥GUS染色及qRT-PCR表明该序列可驱动GUS基因在拟南芥稳定表达,且表达受高盐、渗透压及ABA的诱导。这表明IpDHN-Pro是一个盐旱、ABA诱导的启动子序列,可应用于相关的植物抗逆遗传工程研究。     

Expression of the Granule-Bound Starch Synthase I (Waxy) Gene from Snapdragon Is Developmentally and Circadian Clock Regulated

The granule-bound starch synthase I (GBSSI or waxy) enzyme catalyzes one of the enzymatic steps of starch synthesis. This enzyme is responsible for the synthesis of amylose and is also involved in building the final structure of amylopectin. Little is known about expression of GBSSI genes in tissues other than storage organs, such as seeds, endosperm, and tuber. We have isolated a gene encoding the GBSSI from snapdragon (Antirrhinum majus). This gene is present as a single copy in the snapdragon genome. There is a precise spatial and developmental regulation of its expression in flowers. GBSSI expression was observed in all floral whorls at early developmental stages, but it was restricted to carpel before anthesis. These results give new insights into the role of starch in later reproductive events such as seed filling. In leaves the mRNA level of GBSSI is regulated by an endogenous circadian clock, indicating that the transition from day to night may be accompanied by abolition of expression of starch synthesis genes. This mechanism does not operate in sink tissues such as roots when grown in the dark.     

Field evaluation of transgenic potato plants expressing an antisense granule-bound starch synthase gene: increase of the antisense effect during tuber growth

Transgenic plants of a tetraploid potato cultivar were obtained in which the amylose content of tuber starch was reduced via antisense RNA-mediated inhibition of the expression of the gene encoding granule-bound starch synthase (GBSS). GBSS is one of the key enzymes in the biosynthesis of starch and catalyses the formation of amylose. The antisense GBSS genes, based on the full-length GBSS cDNA driven by the 35S CaMV promoter or the potato GBSS promoter, were introduced into the potato genome by Agrobacterium tumefaciens-mediated transformation. Expression of each of these genes resulted in the complete inhibition of GBSS gene expression, and thus in the production of amylose-free tuber starch, in mature field-grown plants originating from rooted in vitro plantlets of 4 out of 66 transgenic clones. Clones in which the GBSS gene expression was incompletely inhibited showed an increase of the extent of inhibition during tuber growth. This is likely to be due to the increase of starch granule size during tuber growth and the specific distribution pattern of starch components in granules of clones with reduced GBSS activity. Expression of the antisense GBSS gene from the GBSS promoter resulted in a higher stability of inhibition in tubers of field-grown plants as compared to expression from the 35S CaMV promoter. Field analysis of the transgenic clones indicated that inhibition of GBSS gene expression could be achieved without significantly affecting the starch and sugar content of transgenic tubers, the expression level of other genes involved in starch and tuber metabolism and agronomic characteristics such as yield and dry matter content.