Phx22/Sop在拟南芥Lsd1介导的细胞程序性死亡途径中的功能分析

Phytopathogens are major threats to our food supplies and threaten global food security. Research on the molecular mechanisms of plant disease resistance and cell death is our current focus. Programmed Cell death in plants is an ubiquitous and yet tightly controlled genetic process, which can be initiated by a series of fine-tuned signaling pathways, that ultimately results in cell death. Arabidopsis Lsd1 negatively regulates cell death, and lsd1 represents a typical lesion mimic mutant. Further mutagenesis of the lsd1 seeds and mutant screening identified phx22, which suppresses lsd1 type of runaway cell death. Genetic analysis showed that Phx22 is an important regulator of the Lsd1 pathway, and its mutated form, phx22, partially suppresses lsd1 type cell death. We will analyse the product encoded by Phx22 and try to identify its possible substrate(s). To further elucidate the Lsd1 pathway, we mutagenized the seeds of the phx22/lsd1 double mutant by EMS mutagen treatment, and identified three more mutants that we call sop9, sop52 and sop117, which all fully suppressed the partial cell death phenotype in phx22/lsd1 double mutant. Our work will focus mainly on the genetic analyses of the phx22 and the sop mutants. The expanded function of the Phx22 will be revealed by the isolation of the two homologues in Arabidopsis. Sequence analysis revealed that Phx22 encodes a glucosyltransferase, which may be involved in the carbon source molecule transfer of the secondary metabolites, and hence, the substrates of the Phx22 will be determined. This will be carried out by the GC-MS analyses of the samples collected from the cell death induction experiments. As the mutated form of phx22 is unable to transfer certain secondary metabolites, and when compared to the profile of the GC-MS analysis from the wild type Phx22, a differential accumlation pattern of some secondary metabolites may be observed, and therefore, possible candidate substrates of the Phx22 may be identified. Functional test of the candidate substrates in the cell death will then be conducted. Sequence analysis also revealed a few conserved structual domains and a key glucosyltransferase motif of the Phx22 encoded product. Experiments will be carried out to see if these domains or the motif are required for the cell death action. More experiments will be done to test whether Phx22 or Sop9 (Sop52 and Sop117) have any roles in the basal defense observed in the lsd1 plants. Genetic analysis of the double mutants (or triple mutants) with nahG or atrboh lines in the cell death pathway will reveal whether SA or ROS is involved in the Phx22/Sop atcion. Chromosomal positions of the sop9/sop52/sop117 will be determined through genetic mapping, and eventually, we will clone these genes. The functional analysis of the products encoded by these genes may provide more insights to the Lsd1-mediated cell death pathway. All these will undoubtedly facilitate better understanding of the plant defense mechanisms.

植物病原菌威胁食品安全，植物抗病与细胞死亡分子机制是我们研究的重点。拟南芥Lsd1负调控细胞死亡，其突变体lsd1在没有任何病原菌侵染下呈现类病变坏死。phx22突变体部分抑制lsd1细胞死亡表型。研究表明Phx22是Lsd1途径中的一个重要调控因子。我们对phx22/lsd1双突变进行了再次EMS诱变，并得到了完全抑制phx22/lsd1部分细胞死亡表型的突变体sop9、sop52和sop117。我们将对拟南芥中Phx22的两个同源基因进行功能分析，对Phx22蛋白质的作用底物进行探索，对其保守氨基酸结构域与基序在细胞死亡中的作用进行分析。我们还将对SA、ROS与Phx22和Sop的作用关系进行研究；开展sop的染色体定位与分离克隆工作，为进一步的功能分析以及剖析Lsd1介导的细胞程序性死亡途径提供材料。我们的研究也将为了解植物抗病机理奠定基础。

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