Yang Chiao-Yin, Huang Yu-Hsin, Lin Chan-Pin, Lin Yen-Yu, Hsu Hao-Chun, Wang Chun-Neng, Liu Li-Yu Daisy, Shen Bing-Nan, Lin Shih-Shun
Institute of Biotechnology (C.-Y.Y., Y.-H.H., C.-P.L., Y.-Y.L., B.-N.S., S.-S.L.), Genome and Systems Biology Degree Program (S.-S.L.), Department of Plant Pathology and Microbiology (C.-Y.Y., Y.-H.H., C.-P.L., Y.-Y.L.), Institute of Ecology and Evolutionary Biology, Department of Life Science (H.-C.H., C.-N.W.), and Department of Agronomy (L.-Y.D.L.), National Taiwan University, Taipei 106, Taiwan; andAgricultural Biotechnology Research Center, Academia Sinica, Taipei 115, Taiwan (S.-S.L.).
Institute of Biotechnology (C.-Y.Y., Y.-H.H., C.-P.L., Y.-Y.L., B.-N.S., S.-S.L.), Genome and Systems Biology Degree Program (S.-S.L.), Department of Plant Pathology and Microbiology (C.-Y.Y., Y.-H.H., C.-P.L., Y.-Y.L.), Institute of Ecology and Evolutionary Biology, Department of Life Science (H.-C.H., C.-N.W.), and Department of Agronomy (L.-Y.D.L.), National Taiwan University, Taipei 106, Taiwan; andAgricultural Biotechnology Research Center, Academia Sinica, Taipei 115, Taiwan (S.-S.L.)
Plant Physiol. 2015 Aug;168(4):1702-16. doi: 10.1104/pp.15.00307. Epub 2015 Jun 23.
Leafy flowers are the major symptoms of peanut witches' broom (PnWB) phytoplasma infection in Catharanthus roseus. The orthologs of the phyllody symptoms1 (PHYL1) effector of PnWB from other species of phytoplasma can trigger the proteasomal degradation of several MADS box transcription factors, resulting in leafy flower formation. In contrast, the flowering negative regulator gene SHORT VEGETATIVE PHASE (SVP) was up-regulated in PnWB-infected C. roseus plants, but most microRNA (miRNA) genes had repressed expression. Coincidentally, transgenic Arabidopsis (Arabidopsis thaliana) plants expressing the PHYL1 gene of PnWB (PHYL1 plants), which show leafy flower phenotypes, up-regulate SVP of Arabidopsis (AtSVP) but repress a putative regulatory miRNA of AtSVP, miR396. However, the mechanism by which PHYL1 regulates AtSVP and miR396 is unknown, and the evidence of miR396-mediated AtSVP degradation is lacking. Here, we show that miR396 triggers AtSVP messenger RNA (mRNA) decay using genetic approaches, a reporter assay, and high-throughput degradome profiles. Genetic evidence indicates that PHYL1 plants and atmir396a-1 mutants have higher AtSVP accumulation, whereas the transgenic plants overexpressing MIR396 display lower AtSVP expression. The reporter assay indicated that target-site mutation results in decreasing the miR396-mediated repression efficiency. Moreover, degradome profiles revealed that miR396 triggers AtSVP mRNA decay rather than miRNA-mediated cleavage, implying that AtSVP caused miR396-mediated translation inhibition. We hypothesize that PHYL1 directly or indirectly interferes with miR396-mediated AtSVP mRNA decay and synergizes with other effects (e.g. MADS box transcription factor degradation), resulting in abnormal flower formation. We anticipate our findings to be a starting point for studying the posttranscriptional regulation of PHYL1 effectors in symptom development.
叶状花是长春花感染花生丛枝病（PnWB）植原体后的主要症状。来自其他植原体物种的PnWB的叶变症状1（PHYL1）效应器的直系同源物可触发几种MADS盒转录因子的蛋白酶体降解，从而导致叶状花的形成。相比之下，在感染PnWB的长春花植物中，开花负调控基因SHORT VEGETATIVE PHASE（SVP）上调，但大多数微小RNA（miRNA）基因的表达受到抑制。巧合的是，表达PnWB的PHYL1基因的转基因拟南芥（Arabidopsis thaliana）植株（PHYL1植株）呈现叶状花表型，上调了拟南芥的AtSVP，但抑制了AtSVP的一个假定调控miRNA，即miR396。然而，PHYL1调节AtSVP和miR396的机制尚不清楚，且缺乏miR396介导的AtSVP降解的证据。在此，我们通过遗传学方法、报告基因检测和高通量降解组分析表明，miR396触发AtSVP信使核糖核酸（mRNA）的降解。遗传学证据表明，PHYL1植株和atmir396a - 1突变体具有更高的AtSVP积累，而过量表达MIR396的转基因植株显示出较低的AtSVP表达。报告基因检测表明，靶位点突变导致miR396介导的抑制效率降低。此外，降解组分析表明，miR３96触发AtSVP mRNA的降解而非miRNA介导的切割，这意味着AtSVP导致miR396介导的翻译抑制。我们推测，PHYL1直接或间接干扰miR396介导的AtSVP mRNA降解，并与其他效应（如MADS盒转录因子降解）协同作用，导致花的形成异常。我们期望我们的发现成为研究PHYL1效应器在症状发展中的转录后调控的起点。
