Structural Requirements of the Phytoplasma Effector Protein SAP54 for Causing Homeotic Transformation of Floral Organs
Structural Requirements of the Phytoplasma Effector Protein SAP54 for Causing Homeotic Transformation of Floral Organs
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DOI：
10.1094/mpmi-02-20-0028-r
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发表时间：
2020-09-01
影响因子：
3.5
通讯作者：
Theissen, Guenter
中科院分区：
文献类型：
--
作者：
Aurin, Marc-Benjamin;Haupt, Michael;Theissen, Guenter
植原体是一种细胞内细菌性植物病原体，通过分泌效应蛋白在农作物和观赏植物中引起毁灭性疾病。这些效应蛋白之一，被称为分泌紫菀黄女巫扫帚蛋白54（SAP 54），导致降解的特定子集的花同源异型蛋白的MIKC型MADS域家族通过泛素-蛋白酶体途径。因此，发育中的花显示出花器官向营养叶状结构的同源异型转化。SAP 54作用的分子机制涉及与MIKC型蛋白的角蛋白样结构域和一些RAD 23蛋白结合，其将泛素化底物转运至蛋白酶体。然而，SAP 54功能的结构要求和特异性知之甚少。在这里，我们报告，基于生物物理和分子生物学分析，SAP 54折叠成α-螺旋结构。插入螺旋断裂突变破坏了SAP 54的正确折叠，并损害了SAP 54与其靶蛋白的结合，以及伴随的，其在体内引起疾病表型的能力。有趣的是，动态光散射数据连同电泳迁移率变动分析表明，SAP 54优先结合MIKC型蛋白质的多聚体复合物，而不是这些蛋白质的二聚体或单体。结合文献数据，这一发现表明MIKC型蛋白和SAP 54构成多聚体α-螺旋卷曲螺旋。我们的研究澄清了一个重要的植原体效应蛋白的结构-功能关系，从而可能最终有助于开发对一些毁灭性的植物疾病的治疗方法。
Phytoplasmas are intracellular bacterial plant pathogens that cause devastating diseases in crops and ornamental plants by the secretion of effector proteins. One of these effector proteins, termed SECRETED ASTER YELLOWS WITCHES' BROOM PROTEIN 54 (SAP54), leads to the degradation of a specific subset of floral homeotic proteins of the MIKC-type MADS-domain family via the ubiquitin-proteasome pathway. In consequence, the developing flowers show the homeotic transformation of floral organs into vegetative leaf-like structures. The molecular mechanism of SAP54 action involves binding to the keratin-like domain of MIKC-type proteins and to some RAD23 proteins, which translocate ubiquitylated substrates to the proteasome. The structural requirements and specificity of SAP54 function are poorly understood, however. Here, we report, based on biophysical and molecular biological analyses, that SAP54 folds into an alpha-helical structure. Insertion of helix-breaking mutations disrupts correct folding of SAP54 and compromises SAP54 binding to its target proteins and, concomitantly, its ability to evoke disease phenotypes in vivo. Interestingly, dynamic light scattering data together with electrophoretic mobility shift assays suggest that SAP54 preferentially binds to multimeric complexes of MIKC-type proteins rather than to dimers or monomers of these proteins. Together with data from literature, this finding suggests that MIKC-type proteins and SAP54 constitute multimeric alpha-helical coiled coils. Our investigations clarify the structure-function relationship of an important phytoplasma effector protein and may thus ultimately help to develop treatments against some devastating plant diseases.