瘤胃植酸酶转录水平基因多样性及时空表达规律和作用机制研究

Phytase as an eco-enzyme plays an importance role in the phosphate cycle in nature. Rumen is considered as the special environment harboring a typical system for the study of phytase-phosphate relationship, phytase diversity and characteristics, temporal and spatial expression patterns of the phytase and so on. The objective of this study is to obtain a better understanding of the function rules, mechanisms and importance of phytase in rumen environment. Our previous study (supported by the National Science Foundation of China (Grant No. 31001025 )) focused on the static ruminal genome and revealed that 1) cysteine phytase is the major phytate-degrading enzyme in the anaerobic ruminal environment while β-propeller phytase is predominant in the soil and water environment; 2) cysteine phytase fragments from goat and cow rumen contents varies in sequence and abundance but have the same diversity profile and phylogenetic relationship; 3) cysteine phytase has a pH optimum of 6.0–6.5, which is within the rumen pH range but different from the previously reported value (pH 4.5) (Huang et al., Environmental Microbiology, 2011, 13: 747–757; IF 5.5). Based on these results, this study will work on the dynamic transcriptosome of ruminal phytases. The expression patterns of cysteine phytase (including diversity and abundance) within a feeding cycle will be examined. Cysteine phytase representatives will be heterogeneously expressed and characterized. The changing rules of real-time dynamic expression of cysteine phytase and the temporal-spatial expression model of major genes will be revealed. By combining the results from the genetic and transcriptomic studies mentioned above, the functional rules and mechanisms of phytase for phosphate utilization in rumen will be systematically understood.

植酸酶作为生态酶在磷循环中发挥重要作用，瘤胃是植酸酶参与磷循环的特殊而又典型的系统，研究其植酸酶多样性及特征、时空表达规律等，有望加深对植酸酶在瘤胃环境中的功能、作用机制及重要性这一科学问题的理解。承担的青年基金是在静态的环境基因组水平开展的，发现（黄火清等，EM，2011，13, 747–757；IF5.5）：1）与土壤、水体环境中主要为BPP植酸酶不同，在瘤胃环境中是一类新的CP植酸酶；2）不同瘤胃植酸酶有不同的高丰度基因，但多样性和进化关系趋同；3) 植酸酶的最适pH与瘤胃环境一致为6-6.5而不是先前报道的4.5。在前期研究的基础上，本课题进一步在动态的环境转录组水平上，通过一个饲喂周期中瘤胃植酸酶基因表达的多样性、丰度、代表性基因的特征等研究，探索植酸酶实时动态表达的变化规律和主效基因的时空表达模式。综合分析瘤胃基因组和转录组水平的研究结果，系统了解植酸酶在瘤胃中作用规律和机制。

植酸酶作为生态酶在磷循环中发挥重要作用，瘤胃是植酸酶参与磷循环的特殊而又典型的系统，研究瘤胃植酸酶多样性及特征等，加深对植酸酶在瘤胃环境中的功能、作用机制及重要性这一科学问题的理解。本项目的主要内容包括：1）研究不同时间点动态瘤胃环境转录组水平植酸酶基因的多样性、拷贝数和代表性基因的性质，及瘤胃环境因素等，得出在一个饲喂周期内瘤胃环境植酸酶基因的时空表达的变化规律；2）结合青年基金静态瘤胃环境基因组水平植酸酶的研究结果，并探讨植酸酶作为生态酶，在瘤胃环境中的原本功能、作用机制及重要性。本研究主要通过分析比较不同时间植酸酶基因转录水平的变化规律，已取得了较好的研究进展和学术成绩：1）瘤胃植酸酶在转录组和基因组水平存在显著差异，并随着饲喂周期呈现规律性变化；2）在一个饲喂周期内，不同主效的植酸酶基因的转录趋势呈现多样性，说明在不同时期瘤胃环境主效降解植酸的基因会发生变化；3）进化树分析表明， 瘤胃环境中前期发挥主要降解功能的植酸酶主要来源于瘤胃中常见的Firmicutes属的Selenomonnas、Megasphaera、Acidaminococcus和Mitsuokella，16h后主要降解功能的植酸酶来源于一些不可培养微生物。其主要研究结果已在letters in applied microbiology和applied and environmental microbiology杂志上发表，已经较好的完成了任务指标。综合分析瘤胃基因组和转录组水平的研究结果，进一步加深了我们对瘤胃中植酸酶的认识，以及其作用规律和机制。