MYB转录因子对荔枝花色素苷降解的转录调控研究

Litchi (Litchi chinensis Sonn.) is a subtropical fruit with attractive red pericarp and translucent white aril. However, the fruit rapidly loses its red color during storage and becomes less attractive in the market, and the major limitation in litchi marketing is the rapid lose of the red color after harvest. Although litchi fruit can be stored for long time at low temperature, the fruit will deteriorate rapidly due to peel browning when expose to ambient temperature. Postharvest browning of litchi fruit was generally thought to be the results of rapid degradation of anthocyanins caused by the changeable activities of anthocyanase (ANT), peroxidase (POD) and polyphenol oxidase (PPO), but the molecular mechanism of it still remains unkown. It has been demonstrated that MYB proteins are key factors in regulatory networks controlling development, metabolism and responses to biotoic and abiotic stresses, and MYB transcription factor are important in controlling gene expressions of anthocyanin synthesis from the transcriptional level. Based on the previous studies, this study will (1) measure the concentration of anthocyanin, (2) investigate the changeable activities of anthocyanase (ANT), peroxidase (POD) and polyphenol oxidase (PPO) and (3)profile alterations of MYB transcription factor and gene expression of ANT, POD and PPO in litchi fruit both cold-stored and exposed to ambient temperature, (4) screen the MYB transcription factor which transcriptionally regulate ANT, POD and PPO gene expression. It will be helpful to interpret the mechanism of anthocyanin degradation of litchi fruit both at physiology and molecular level, and provide new ideas for alleviating anthocyanin degradation of litchi fruits in practice.

荔枝采后短时间内就发生褐变和腐烂变质，冷藏是最有效的保鲜方法，但低温贮藏的荔枝出库后常温货架期比未经冷藏的鲜果更短，褐变速率更快。国内外主要从酶促褐变的角度研究了荔枝中花色素苷的降解，但相关的分子机理尚未明确。本项目拟从MYB转录因子调控花色素苷降解中相关基因表达的角度研究荔枝中花色素苷迅速降解的现象，主要研究低温贮藏期和常温货架期中1）荔枝果皮花色素苷的含量变化；2）花色素苷酶（ANT）、多酚氧化酶（PPO）和过氧化物酶（POD）活性变化；3）MYB转录因子、ANT、PPO和POD基因的表达变化，和4）筛选具有转录调控ANT、PPO和POD基因表达的MYB转录因子。研究结果可望从分子生物学角度阐明花色素苷降解的机理，证实MYB转录因子在花色素苷降解过程中的转录调控作用。本项目研究成果在理论上可丰富花色素苷降解的发生发展机制；在实践上，为进一步探讨减缓荔枝果实花色素苷降解的技术提供新思路。

项目背景：.荔枝采后短时间内就发生褐变和腐烂变质，冷藏是最有效的保鲜方法，但低温贮藏的荔枝出库后常温货架期比未经冷藏的鲜果更短，褐变速率更快。国内外主要从酶促褐变的角度研究了荔枝中花色素苷的降解，但相关的分子机理尚未明确。.主要研究内容：.从MYB转录因子调控花色素苷降解中相关基因表达的角度研究荔枝中花色素苷迅速降解的现象，主要研究低温贮藏期和常温货架期中1）荔枝果皮花色素苷的含量变化；2）花色素苷酶（ANT）、多酚氧化酶（PPO）和过氧化物酶（POD）活性变化；3）MYB转录因子、ANT、PPO和POD基因的表达变化，和4）筛选具有转录调控ANT、PPO和POD基因表达的MYB转录因子。.关键数据：.1）低温和常温贮藏期间荔枝果皮中花色素苷含量、H2O2和MDA含量； .2）低温和常温贮藏期间荔枝果皮PPO、POD、SOD、CAT酶和ANT酶活性的变化；.3）对低温和常温贮藏期间荔枝果皮进行转录组测序及分析；.4）基于转录组信息，集中分析常温贮藏期间与氧化褐变、花色素苷降解等过程相关的基因，筛选出基因表达显著变化的PPO（2个）、POD（14个）、SOD（10个）和CAT（3个）基因并进行RT-PCR鉴定；.5）筛选出基因表达显著变化的MYB转录因子（17个）并进行RT-PCR鉴定，初步确定MYB转录因子参与了荔枝常温贮藏期间氧化褐变、花色素苷降解等生物学进程；.6）利用新合成的新型抑菌剂(1,2,3-噻重氮-4-羰基)-氨基甲酸己酯［Carbamic acid, (1,2,3-thiadiazole-4-ylcarbonyl)-, hexyl ester；CTE］，筛选CTE体外抑制荔枝霜疫霉菌的MIC和MFC浓度，进一步研究表明外源CTE处理抑制了荔枝果实的褐变和病害发生，提高了果实品质。CTE处理在提高荔枝果皮中POD酶活性水平的同时，降低了PPO酶活性，减缓了荔枝果皮的褐变。.科学意义：.研究结果可望从分子生物学角度阐明花色素苷降解的机理，证实MYB转录因子并非仅参与花色素苷合成的途径中，也参与花色素苷的降解过程。本项目研究成果在理论上可丰富花色素苷降解的发生发展机制；在实践上，为进一步探讨减缓荔枝果实花色素苷降解的技术提供新思路。