圖1. 捕蠅草經常張開葉片，等待獵物接觸葉子表面上的微小觸發毛。
The jaws of the Venus flytrap are open, waiting for prey to touch the tiny trigger hairs on the leaf surface.
An insect lands on the open leaves of a Venus flytrap plant, drawn to an appealing scent. It noses around and accidentally brushes one of the trap’s trigger hairs. An action potential shoots across the leaf blade.
一隻昆蟲被吸引到誘人的氣味處，著落於一棵捕蠅草植物張開的葉子上。它四處嗅探，不經意輕碰到該捕蠅器的觸發毛之一。一個動作電位極速傳遍此葉片。
The insect keeps moving and bends another trigger hair, propagating a second action potential; suddenly, the leaves snap shut, trapping the insect, enveloping it in digestive juices, and absorbing the bug’s rich nutrients.
此昆蟲繼續移動且彎曲另一根觸發毛，傳播第二個動作電位；突然，葉子迅速閉合，陷捕住該昆蟲，將其封包於消化液中，同時吸收此昆蟲豐富的養分。
How these two light touches trigger abrupt shutting of the leaves has been hypothesized, but never proven. Now, in a new study published in Current Biology, a team of researchers knocked out two ion channels, making it harder to produce action potentials and proving the channels’ importance in leaf closing.
人們已經假設了，上述兩次輕觸，如何觸發葉子突然閉合。不過，未曾經證實。目前，在發表於《當代生物學》期刊的一項新研究中，一支研究人員團隊剔除了兩個離子通道，使其較難產生動作電位。然後證實了這些通道，在葉子閉合上的重要性。
“The paper is a very big technical advance,” said plant biophysicist Rainer Hedrich at the University of Wurzburg who was not involved in the study. “It is possible to knock out genes in an excitable plant and test hypotheses.”
德國維爾茨堡大學，未涉及這項研究的植物生物物理學家，Rainer Hedrich宣稱：「此篇論文是一項，非常大的技術進展。剔除對刺激易於感應之植物中的基因，並測試諸多假設是可能的。」
圖2. Carl Procko在溫室裡拿著一株，儲存著各種基因轉移及野生型的捕蠅草植物。
Carl Procko holds a Venus flytrap plant in the greenhouse that stores various transgenic and wild type plants
Carnivorous plants and their quick movements have fascinated scientists for centuries. In the 1870s, Darwin and his colleagues discussed how electrical currents played a role in leaf closing.
幾個世紀以來，食蟲類植物及其快速動作，一直令科學家們感到迷惑。於1870年代，達爾文及其同僚們討論過，電流如何在葉子閉合上，扮演一種角色。
More recently, scientists found mechanosensitive ion channels FLYCATCHER1 (FLYC1) and FLYCATCHER2 (FLYC2) expressed in trigger hairs that may associate with touch sensitivity. Even though the Venus flytrap’s genome is sequenced, no targeted mutations of ion channel genes have been made to conclusively prove their roles in leaf closing.
最近，於觸發毛中，科學家們發現了，可能與碰觸敏感度有關之經表現的機械性敏感離子通道，FLYCATCHER1 (FLYC1)及FLYCATCHER2 (FLYC2)。即使捕蠅草的基因體已被排序，不過無經鎖定之離子通道基因的突變體，已經被獲得來結論性證實，它們在葉子閉合上的角色。
So, plant biologists Carl Procko and Joanne Chory at the Salk Institute decided to use CRISPR-Cas9 to mutate FLYC1 and FLYC2 to investigate their functions. Scientists had hypothesized that an insect’s touch causes deformation of the trigger hair’s sensory cell membrane, which causes the opening of these ion channels and membrane depolarization and electrical signaling.
因此，美國索爾克生物研究所，植物生物學家Carl Procko及Joanne Chory決定使用CRISPR-Cas9[群聚、規律性間隔開的短迴文結構複製(CRISPR：Clustered Regularly Interspaced Short Palindromic Repeat)-Cas9(CRISPR associated protein 9：是一種在某些細菌對DNA病毒之免疫防禦中，起至關重要作用的蛋白質)]，來使FLYC1及FLYC2突變，以調查研究它們的功能。科學家們曾經假設，昆蟲的碰觸導致，觸發毛的感知細胞膜變形，而導致開啟此些離子通道，及細胞膜去極化並發出電氣信號。
Procko grew Venus flytrap plants in tissue culture and then fired gold particles covered with plasmid DNA containing components of the CRISPR-Cas9 system into the cells. In the plasmid, the researchers also included a gene for a fluorescent protein to identify the plasmid-bearing tissue.
於組織培養物中，Procko培養了捕蠅草植物。然後，將覆蓋有CRISPR-Cas9體系成分之質體(指在細胞的染色體或核區DNA之外，能夠自主複製的DNA分子)DNA的金粒子，射入細胞中。為了獲得一種，用來確認具有該質體的組織。此些研究人員，於該質體中，也添加了一個螢光蛋白質的基因。
The team propagated the genetically transformed cells and eventually grew a new plant. The plant was mosaic; it carried the plasmid DNA in some leaf arms, while others were wild type.
該團隊繁殖了此些經基因轉化的細胞，結果最終培育了新植物。該種植物是拚花式的；其在某些葉臂中，具有質體DNA，而其他葉臂是野生型。
Procko chose leaflets that were fully transgenic (and fluorescent) and clonally separated them in tissue culture. To determine whether the leaves were single or double mutants, Procko used PCR-based Sanger sequencing and genotyping. He chose single mutants for some experiments and double mutants for others. He then planted the plants in soil and continued to grow them in a greenhouse.
Procko選擇完全基因轉移(及發螢光)的小葉，並在組織培養中，使無性繁殖地分離它們。為了確認此些葉子是單突變或雙突變，Procko使用了，以聚合酶連鎖反應為基礎的桑格排序法及基因分型法，為一些實驗選擇單突變，為其他實驗選擇雙突變。然後，將這些植物種植於土壤中，並繼續於溫室中種植。
Next, he triggered the double mutant plants with a touch from thin, fire-polished glass rod mounted on a micromanipulator; they closed just as often and as quickly as the wild type plants.
接下來，使用來自安裝在顯微操縱器上，經火拋光之細玻璃棒的碰觸，來觸發這些雙突變植物；它們一樣屢屢關閉且速度與野生型植物一樣快。
“You get a plant that looks normal,” said Procko. “You sit there, and you scratch your head a bit.” Procko thought that perhaps the defect was smaller than could be detected using the relatively large touch of a pipette and decided to search for another more subtle quantitative assay.
Procko宣稱：「獲得了一株看來正常的植物。坐在那裡，搔頭片刻。」Procko認為，或許缺陷比使用相對較大之移液器的碰觸，能察覺的小。因此，決定尋找另一種，更精細的定量分析法。
圖3. Sreekanth Chalasani實驗室的科學家，Wen Mai Wong使用超音波能量變換器，來測試捕蠅草葉子的動作電位。
Wen Mai Wong, a scientist in Sreekanth Chalasani's lab, uses the ultrasound transducer to test a Venus flytrap leaf for its action potential.
He collaborated with molecular neurobiologist Sreekanth Chalasani, also at the Salk Institute, who works with ultrasound. When the team tested the plants with a new, more sensitive assay using ultrasound waves to stimulate the trigger hair, the FLYC1-FLYC2 double mutants showed a significant defect:
他與同樣在索爾克研究所，從事超音波研究的分子神經生物學家，Sreekanth Chalasani合作。當該研究團隊以一種，使用超音波來刺激觸發毛之更靈敏的新方法，測試此些植物時。FLYC1-FLYC2雙突變體展現了，顯著的缺陷：
mutated plants required a greater ultrasound pressure to induce the trap closure than wild type plants. The team noted that single FLYC1 mutants stimulated with ultrasound closed just as well as the wild type plants. Procko believes that brute force mechanical stimulation with the glass rod may be so large that it could act through different mechanosensitive ion channels in the trigger hair.
經突變的植物需要，比野生型植物更大的超音波壓力，來誘發捕蠅器閉合。該團隊特別指出，以超音波刺激的單FLYC1 突變體，閉合與野生型植物一樣。Procko認為，使用玻璃棒的強力機械性刺激，可能非常大以至於，它可以透過觸發毛中，不同的機械性敏感離子通道起作用。
“The next step now is to start looking at these other mechanosensitive channels that are within the trigger hair,” said Procko. “We can start to mutate some of these others and put them in various combinations to see exactly which mechanosensitive channels are most important or if they’re all required together to get that very exquisite touch sensitivity of the trigger hair.”
Procko宣稱：「目前，下一步是開始探究，觸發毛中的其他機械性敏感通道。我們會開始改變其中一些其他通道，並將它們放入各種組合中，以確切瞭解，哪些機械性敏感通道最重要，或是否它們需要全部組合在一起，以獲得觸發毛非常敏銳的碰觸敏感度。」
Hedrich’s team is currently working to knock out a calcium channel gene hyperosmolality-gated calcium-permeable channel (OSCA). Procko acknowledged that he didn’t know exactly how the ultrasound assay relates to touch, which limits the study.
目前，Hedrich的團隊正致力於剔除，高滲透壓閘門之鈣可滲透通道(OSCA)的鈣通道基因。Procko承認，他並不確切知曉，超音波分析如何與碰觸有關聯，這限制了該項研究。
“It’s a mechanical stimulus. We like to think it’s related to touch, but it could alternatively be applying that stimulus directly to the sensory membranes and altering the membranes. So, this is still a little bit of a question mark,” said Procko.
Procko宣稱：「這是一種機械性刺激。我們想認為，這與碰觸有關。不過它也可能是，將刺激直接施加到感覺膜，而改變此些膜。因此，這仍然有點問號。」
網址：https://www.the-scientist.com/news/how-the-venus-flytrap-captures-its-prey-71429
翻譯：許東榮
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