PHO 2 , MicroRNA 399 , and PHR 1 Define a Phosphate-Signaling Pathway in Plants 1 [ W ] [ OA ]
PHO 2 , MicroRNA 399 , and PHR 1 Define a Phosphate-Signaling Pathway in Plants 1 [ W ] [ OA ]
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发表时间：
2006
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通讯作者：
R. Bari;B. Pant;M. Stitt;W. Scheible
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作者：
R. Bari;B. Pant;M. Stitt;W. Scheible
植物中的无机磷酸盐信号通路在很大程度上仍然是未知的。拟南芥（Arabidopsis thaliana） pho2突变体在Pi充满条件下在叶片中过度积累Pi。显微嫁接表明，pho2根基因型足以产生叶片Pi积累。在光突变体中，Pi不抑制一组Pi饥饿诱导基因，包括AtIPS1、AT4和Pi转运蛋白Pht1；8、Pht1；基于图谱的克隆鉴定PHO2为罕见的E2偶联酶基因At2g33770。最近的研究表明，Pi剥夺诱导成熟的microRNA (miRNA [miR399])，在Pi充满的条件下，miR399的过表达抑制E2偶联酶的表达，导致叶片Pi浓度高，从而表型复制pho2。我们在这里表明，miR399初级转录本也受到低Pi的强烈诱导，并在加入Pi后迅速被抑制。在pi缺失植物和miR399过表达者中，PHO2转录物与miR399转录物相互改变。然而，Pi读取后和b-葡糖醛酸酶报告系的反应表明，PHO2的表达也受到Pi的调节，与mir399介导的转录物切割无关。在pi缺失的拟南芥phr1突变体中，miR399的表达强烈降低，而在pi缺失的phr1突变体中被抑制的一个pi应答基因子集在pi充满的pho2突变体中被上调。这将miR399和PHO2置于PHR1下游的pi信号网络分支中。最后，在其他高等植物中发现了PHO2同源物在其5#-非翻译区含有5个miR399结合位点，并且在水稻（Oryza sativa）中证实了pi依赖的miR399表达，表明其具有保守的调控机制。
Inorganic phosphate (Pi)-signaling pathways in plants are still largely unknown. The Arabidopsis (Arabidopsis thaliana) pho2 mutant overaccumulates Pi in leaves in Pi-replete conditions. Micrografting revealed that a pho2 root genotype is sufficient to yield leaf Pi accumulation. In pho2mutants, Pi does not repress a set of Pi starvation-induced genes, including AtIPS1, AT4, and Pi transporters Pht1;8 and Pht1;9. Map-based cloning identified PHO2 as At2g33770, an unusual E2 conjugase gene. It was recently shown that Pi deprivation induces mature microRNA (miRNA [miR399]) and that overexpression of miR399 in Pi-replete conditions represses E2 conjugase expression and leads to high leaf Pi concentrations, thus phenocopying pho2. We show here that miR399 primary transcripts are also strongly induced by low Pi and rapidly repressed after addition of Pi. PHO2 transcripts change reciprocally to miR399 transcripts in Pi-deprived plants and in miR399 overexpressers. However, responses after Pi readdition and in b-glucuronidase reporter lines suggest that PHO2 expression is also regulated by Pi in a manner unrelated to miR399-mediated transcript cleavage. Expression of miR399 was strongly reduced in Pi-deprived Arabidopsis phr1 mutants, and a subset of Pi-responsive genes repressed in Pi-deprived phr1 mutants was up-regulated in Pi-replete pho2 mutants. This places miR399 and PHO2 in a branch of the Pi-signaling network downstream of PHR1. Finally, putative PHO2 orthologs containing five miR399-binding sites in their 5#-untranslated regions were identified in other higher plants, and Pi-dependent miR399 expression was demonstrated in rice (Oryza sativa), suggesting a conserved regulatory mechanism.