The Pht1;9 and Pht1;8 transporters mediate inorganic phosphate acquisition by the Arabidopsis thaliana root during phosphorus starvation

? The activation of high-affinity root transport systems is the best-conserved strategy employed by plants to cope with low inorganic phosphate (Pi) availability, a role traditionally assigned to Pi transporters of the Pht1 family, whose respective contributions to Pi acquisition remain unclear. ? To characterize the Arabidopsis thaliana Pht1;9 transporter, we combined heterologous functional expression in yeast with expression/subcellular localization studies and reverse genetics approaches in planta. Double Pht1;9/Pht1;8 silencing lines were also generated to gain insight into the role of the closest Pht1;9 homolog. ? Pht1;9 encodes a functional plasma membrane-localized transporter that mediates high-affinity Pi/H? symport activity in yeast and is highly induced in Pi-starved Arabidopsis roots. Null pht1;9 alleles exhibit exacerbated responses to prolonged Pi limitation and enhanced tolerance to arsenate exposure, whereas Pht1;9 overexpression induces the opposite phenotypes. Strikingly, Pht1;9/Pht1;8 silencing lines display more pronounced defects than the pht1;9 mutants. ? Pi and arsenic plant content analyses confirmed a role of Pht1;9 in Pi acquisition during Pi starvation and arsenate uptake at the root-soil interface. Although not affecting plant internal Pi repartition, Pht1;9 activity influences the overall Arabidopsis Pi status. Finally, our results indicate that both the Pht1;9 and Pht1;8 transporters function in sustaining plant Pi supply on environmental Pi depletion.     

油菜矮秆突变WRKY转录因子cDNA克隆及表达分析

以甘蓝型油菜为材料,利用已建立的抑制性消减文库(SSH),采用RACE技术克隆到1个植物WRKY转录因子相关基因,命名为BnD11,其cDNA全长1034 bp,含有810 bp的完整开放阅读框,编码269个氨基酸。该基因编码的氨基酸序列与拟南芥WRKY40氨基酸序列相似性为79%,与拟南芥中编码WRKY-DNA结合蛋白40基因的氨基酸序列相似性达78%,与其它多种植物的WRKY转录因子的氨基酸序列也有较高的相似性。半定量RT-PCR对BnD11进行组织特异性表达分析显示:在正常生长条件下,BnD11在野生型和矮秆油菜的各个组织中均有表达,但在矮秆突变的根、茎、茎尖的相对表达量明显高于野生型。研究表明,BnD11功能区段具有很高的保守性,可能参与了油菜的茎秆发育。     

The protein kinases AtMAP3Kepsilon1 and BnMAP3Kepsilon1 are functional homologues of S. pombe cdc7p and may be involved in cell division

We identified an Arabidopsis thaliana gene, AtMAP3Kepsilon1, and a Brassica napus cDNA, BnMAP3Kepsilon1, encoding functional protein serine/threonine kinases closely related to cdc7p and Cdc15p from Schizosaccharomyces pombe and Saccharomyces cerevisiae, respectively. This is the first report of cdc7-related genes in non-fungal eukaryotes; no such genes have as yet been identified in Metazoans. The B. napus protein is able to partially complement a cdc7 loss of function mutation in S. pombe. RT-PCR and in situ hybridisation revealed that the A. thaliana and B. napus genes are expressed in both the sporophytic and the gametophytic tissues of the respective plant species and revealed further that expression is highest in dividing cells. Moreover, AtMAP3Kepsilon1 gene expression is cell cycle-regulated, with higher expression in G2-M phases. Our results strongly suggest that the plant cdc7p-related protein kinases are involved in a signal transduction pathway similar to the SIN pathway, which positively regulates cytokinesis in S. pombe.     

<Emphasis Type="Italic">MAX4</Emphasis> gene is involved in the regulation of low inorganic phosphate stress responses in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

MAX4 gene has been shown to be involved in the regulation of shoot branching in Arabidopsis (Arabidopsis thaliana). However, little is known about the role of MAX4 gene in low inorganic phosphate (Pi) stress response in Arabidopsis. Here we showed that MAX4 gene is involved in the regulation of low Pi stress response in Arabidopsis. MAX4 gene was repressed by low Pi stress, and the max4 mutants showed lower anthocyanin content and longer primary root length. In addition, max4 mutant plants also displayed altered root architecture such as increased root-to-shoot ratio, lower lateral root number and root hair density compared with wild-type plants under low Pi stress. Higher total Pi contents were detected in shoots and roots of max4 plants than those of wild-type plants when subjected to low Pi stress, which was associated, at least in part, with increase in expression of WRKY75 as well as AtPT1 and AtPT2 genes encoding high-affinity Pi transporters. Taken together, all these results suggest that MAX4 gene mediates low Pi stress response, at least in part, by regulating the expression of WRKY75 as well as AtPT1 and AtPT2 genes.