生長素及生長素響應因子SsARF3 對大岩桐背腹花瓣建立的影響

Abstract

兩側對稱的花朵能夠藉由限制專一傳粉者拜訪促進物種豐度，因此在被子植物中具有演化優勢。過去在金魚草（Antirrhinum）的研究中，發現CYCLOIDEA（CYC）基因能夠透過調控MYB轉錄因子家族提供背側花瓣特徵，並在花瓣建立背腹側極性，然而還有哪些下游轉錄因子參與其中尚不清楚。大岩桐（Sinningia speciosa ‘Espirito santo’）為兩側對稱花，且有較大的背側花瓣與較小的腹側花瓣。分析大岩桐背腹側花瓣轉錄體後，找出許多生長素訊息傳遞路徑相關基因（如生長素響應因子ARF3，AUXIN RESPONSE FACTOR 3）在背側花瓣高度表現，顯示生長素的調節可能與花瓣背腹側極性建立有關。我利用液向層析串聯式質譜儀在背側花瓣中偵測到較高含量的內生性生長素，並將花苞處理生長素抑制劑後，觀察到花瓣生長受到影響，如背側花瓣的長度縮短。經由雙螢光素酶證實SsARF3與SsCYC間有正向相互促進的關係。為了驗證SsARF3的基因功能，我透過比較阿拉伯芥轉殖株的性狀確認SsARF3為抑制子，在過度表現SsARF3-GFP與SsARF3-SRDX嵌合蛋白之轉植株中，皆有著較大的花瓣面積、較大的花瓣細胞，與縮短的初級花序。這些結果暗示生長素與SsARF3可能與SsCYC合作影響大岩桐背腹花瓣建立。

Floral zygomorphy (bilateral symmetry) prevails in angiosperms and greatly enhances specific pollinators visits, thus promoting species richness. In Antirrhinum, the CYCLOIDEA (CYC) gene established zygomorphy by providing dorsal petal identity, but the downstream regulation except the MYB-like gene family remains unknown. Wild-type Sinningia speciosa ‘Espírito santo’ (Gloxinia) is zygomorphic by having its dorsal petals larger than the ventral petals. From a petal transcriptomic analysis in S. speciosa, most auxin signaling pathway genes, such as AUXIN RESPONSE FACTOR 3 (SsARF3), are highly expressed in dorsal petals, suggesting that auxin regulation is involved in dorsi-ventral petal asymmetry. Here, the endogenous IAA level in dorsal petals is higher than ventral petals, as determined by UPLC/MS/MS. NPA (auxin inhibitor) treatment affected petal growth by reducing the length of dorsal corolla tube. The positive regulation between SsCYC and SsARF3 was examined by a dual luciferase assay. Phenotypic analysis in Arabidopsis transgenic plants inferred that SsARF3 was a repressor, as was the SsARF3-SRDX fusion protein, which functions to promote petal cell expansion and reduce primary inflorescence. These results suggest that auxin and SsARF3 may coordinate with SsCYC for establishment of dorsi-ventral petal asymmetry.