MADS轉錄因子中之 (MADS domain transcription factors, MTFs) 藉由轉錄因子中之 Keratin-like (K) 結構域組合成不同的四聚體影響其目標基因的表達,而調控花輪 (floral whorl) 的發育,即 ABCE 模組。其中 SEPALLATA3 (SEP3) 對於花器的形成與花器分化是最為重要的,是葉分化成花的關鍵基因。先前的研究中,洋蔥黃化病菌質體 (onion yellows phytoplasma ,OY) 之效應蛋白 PHYL1 亦造成 SEP3 降解,使植物產生葉狀花之病徵。我們的研究指出,花生簇葉菌質體 (Peanut witches' broom phytoplasma, PnWB) 的 PHYL1 晶體結構類似於 MTFs 的 K 結構域。在我們的初步研究中確定了 SEPALLATA3(SEP3_K) 的 PHYL1 和 K 結構域之間的四個可能的相互作用位點(I25,Y32,L60和Y64)。我們推測 PHYL1 通過與 K 結構域競爭干擾 MTFs 四聚體的形成,從而引發 SPE3 降解。 YFP 融合野生型 PHYL1(YFP-PHYL1WT) 和3種 PHYL1 突變體 (YFP-PHYL1I25KY32K,YFP-PHYL1L60SY64K和YFP-PHYL1I25KY32KL60SY64K) 在菸草上與 SEP3_K-CFP 暫時性共表現後,通過共定位分析和免疫沉澱評估它們的交互作用。我們發現 SEP3_K,PHYL1 和 PHYL1 中的突變體在細胞核和細胞質中表達並於同一位置。然而,免疫沉澱結果表明僅 PHYL1WT 和 PHYL11I25KY32K 與 SEP3_K 相互作用。此外,由 PHYL1WT,PHYL1I25KY32KL60SY64K 與全長 SEP3 共同暫時性表現在煙草上。共聚焦顯微鏡觀察結果表明 PHYL1WT 觸發 SEP3 降解,而 PHYL1I25KY32KL60SY64K 未觸發 SEP3 降解,因為失去了蛋白質-蛋白質相互作用。總之,推測此4個關鍵氨基酸能與 SEP3 的 K 結構域相互作用以觸發整個 SEP3 降解。
MADS transcription factors (MTFs) regulate the development of floral whorl through self-interaction by Keratin-like (K) domain of MADS. Among of them, SEPALLATA3 (SEP3) is the most important MTFs. In previous studies, the effector of PHYL1 of onion yellows phytoplasma causes SEP3 degradation and leafy flowers (phyllody) formation. Our data indicated that PHYL1 crystal structure of Peanut witches' broom phytoplasma (PnWB) is similar to the K domain of MTFs. Four possible interacting sites (I25, Y32, L60, and Y64) between PHYL1 and K domain of SEPALLATA3 (SEP3_K) were identified in our preliminary data. We suggest that PHYL1 interferes MTF tetramer formation through competing with K domain, resulting in triggering SPE3 degradation. The YFP fused wild type PHYL1 (YFP-PHYL1WT) and 3 PHYL1 mutants (YFP-PHYL1I25KY32K, YFP-PHYL1L60SY64K, and YFP-PHYL1I25KY32KL60SY64K) were transiently expressed on Nicotiana benthamiana with SEP3_K-CFP for evaluating their interaction by colocalization and immunoprecipitation (IP). We found that among of SEP3_K, PHYL1, and PHYL1 mutants are express at nucleus and cytoplasm. In addition, these proteins colocalize at nucleus and cytoplasm. However, the IP results indicated that PHYL1WT and PHYL1I25KY32K interact with SEP3_K in vivo. Moreover, the SEP3 were performed with PHYL1WT and PHYL1I25KY32KL60SY64K on N. benthamiana by transient expression. The confocal results indicated that PHYL1WT triggers SEP3 degradation, whereas PHYL1I25KY32KL60SY64K did not trigger SEP3 degradation because lost the physical protein-protein interaction. In conclusion, the 4 critical amino acids are responded for interaction with K domain of SEP3 for triggering the whole SEP3 degradation.