产毒和非产毒拟柱孢藻的磷吸收转运通路基因比较及对低磷的响应表达特征分析

Comparative analysis of phosphorus uptake and transport pathway genes between toxic and non-toxic Cylindrospermopsis raciborskii and their responses to low phosphorus

拥有完整的磷吸收转运通路基因(Pho调节子)是蓝藻适应环境磷波动的分子基础,目前对这些基因在拟柱孢藻(Cylindrospermopsis raciborskii)中的响应表达特征还知之甚少。本研究在拟柱孢藻非产毒株N8前期工作的基础上,分析产拟柱孢藻毒素(cylindrospermopsin, CYN)藻株QDH7中Pho调节子基因的组成,并比较两藻株在高磷和低磷下的生长、碱性磷酸酶(alkaline phosphatase, ALP)活性及8个Pho调节子基因的时序表达。结果表明, QDH7和N8的Pho调节子基因均很完整,主要在排列和少数基因的拷贝数上存在差异。低磷下两藻株的生长都受到明显抑制, ALP活性在第14~18天显著升高,而产毒和非产毒藻株在相同磷浓度下的生长趋势基本一致。基因的时序表达分析表明,低磷下两藻株的双组份系统基因phoB和phoR在第4~6天和第14~16天有显著的表达升高,而2个高亲和力无机磷结合蛋白基因中仅pstS1的表达显著升高, 2个ALP基因中phoA1的表达与酶活性的增加基本同步,表明pstS1和phoA1基因在对低磷的响应中起主要作用;低亲和力无机磷转运系统pit在低磷处理第16~18天的表达上调可能是QDH7和N8极度缺磷状态的指示。我们发现低磷下产毒株QDH7有6个基因的最高相对表达量高于非产毒株N8,这种差异在磷不足的环境中可能会影响共存于自然水体中的2种基因型藻株对磷的竞争和相对优势的形成。

The molecular basis for cyanobacteria to adapt to environmental phosphorus fluctuations is to have complete phosphorus uptake and transport pathway genes(Pho regulon).Currently,little is known about the response and expression pattern of these genes in Cylindrospermopsis raciborski.Based on our previous study on the non-toxic C.raciborskii N8,Pho regulon genes in the CYN-producing strain QDH7 were further analyzed,and compared the growth,alkaline phosphatase(ALP)activity,and temporal ex-pression of eight Pho regulon genes of the two strains under high and low phosphorus(P)conditions.The results showed that the Pho regulon genes of both strains were relatively complete,with some differences in arrangement and copy number of several genes.Under low P concentration,the growth of both strains was significantly inhibited,and the ALP activity significantly increased between days 14 to 18.The growth trend of toxic and non-toxic strains was almost consistent under the same P concentration.Both strains significantly increased the expression of two component regulatory system genes phoB and phoR during days 4 to 6 and 14 to 16,while only one of the two high affinity inorganic P binding protein genes psts1 showed a significantly increased expression.Among the two ALP genes,the expression of phoA1 was synchronized with an increase in ALP activity.These findings indicated that the psts1 and phoA1 genes played a crucial role in the response to low P.The upregulation of the low affinity inorganic P transport system pit during days 16 to 18 may be an indication of extreme P deficiency in the strain QDH7 and N8.We found that the maximal relative expression levels of six genes of toxic QDH7 under low P were higher than those of non-toxic N8.This difference may affect the competition for phosphorus and the formation of relative advantage between the two genotype strains coexisting in natural water bodies in phosphorus deficient environments.