Wolffia australiana belongs to the subfamily Lemnaceae within the family Araceae. It is not only the smallest but also the simplest angiosperm. The tiny ellipsoidal morphological structure of Wolffia can be summarized by the "four ones": about ONE mm in length and diameter, ONE leaf (although a growth tip and multiple branches are enclosed inside the ellipsoidal leaf), and usually only ONE stamen and ONE pistil when flowering.
Records of this type of duckweed plants in China can be traced back to the Spring and Autumn Period and the Warring States Period. People assigned the name according to its growth characteristics: "Floating without roots on the water surface, so it is called Ping” (meaning even to the water level. the duckweeds). The ancients have realized the characteristics of duckweed plants that quickly produce new individuals: "The duckweed breeds so well that it produces seven descendants overnight". But regarding the origin of the duckweed, some people proposed romantic imagination of poplar flowers falling into the water and turning into duckweed. Literati had analogized the uncertainty of life with the rootlessness of the duckweed (Ping): "Every piece of duckweed floats down to the sea; People will always meet each other somewhere".
In the field of modern science, there have been two research upsurges on duckweed. The first began in the 1950s, represented by Swiss botanist Elias Landolt. He collected and preserved more than 1000 duckweed (including Wolffia) germplasm resources, and described the morphological characteristics of the duckweed in detail. William Hillman, an American plant physiologist, tried to use duckweed as a model organism to study plant physiology and biochemistry. The second was represented by the American molecular biologist Eric Lam, hoping to take advantage of the rapid growth of duckweed plants to develop it into a bioreactor. The number of scientists participating in this upsurge has increased, and the genome sequencing and genetic modification technology of several duckweed (including Wolffia) species have also been established.
The original intention of the establishment of this website is different from the two research upsurges mentioned above. We hope to build a data sharing platform based on the research findings obtained by our team and make it a communication space for people interested in exploring the basic principles of plant morphology.
Our research on Wolffia can be dated back to 1994. At that time, Dr. Shu-Nong Bai, who had just finished his postdoctoral training at the UC Berkeley, introduced his newly developed concept "plant developmental unit" to Prof. Da-Ming Zhang, a classmate of Shu-Nong Bai during their PhD studies at the Institute of Botany, Chinese Academy of Sciences (CAS). Prof. Da-Ming Zhang proposed that Wolffia could be used as an experimental system to test the concept of "plant developmental unit", and he was the first to start a new attempt to establish Wolffia as a model plant. A few years later, Da-Ming Zhang at the Institute of Botany, led his students to complete the collection of Chinese Wolffia germplasm resources and laboratory aseptic culture and preservation. However, his efforts were unsustainable due to the inability to achieve flowering induction in the laboratory in Beijing.
Seeing that his friend’s attempts were in trouble, Dr. Shu-Nong Bai, who had already moved from the Institute of Botany to the Peking University (PKU), learnt a new technology called microfluidic from a leading scientist, Professor Yong Chen of the Ecole Normale Supérieure Paris, when both of them were members of the Center for Theoretical Biology (later renamed as the Center for Quantitative Biology, CQB) at PKU. Understanding the potential advantages of microfluidic technology in high-throughput optimization of culture conditions, they proposed to the center colleagues to expand "microfluidics" to "millifluids" to optimize the flowering induction conditions of microfluidics. So the concept of "plant-on-chip" came into being in the CQB. The experiments were launched in the laboratory of Shu-Nong Bai in the School of Life Science (SLS) in 2007, in collaboration with Prof. Qi Ouyang and Prof. Chun-Xiong Luo in the School of Physics. Unfortunately, although this attempt made people gain a lot of first-hand knowledge about Wolffia morphogenesis, the goal of flower induction was not achieved by 2010.
Around 2013, Prof. Hong-Wei Hou from the Institute of Hydrobiology of CAS was convinced to join the research team of Wolffia because of his laboratory located in Wuhan (Wolffia can bloom every year in the water body of the Wuhan Botanical Garden). Prof. Da-Ming Zhang gifted Prof. Hou all his Wolffia samples he had carefully collected for many years.
In 2016, due to various coincidences, Wolffia research has reappeared in the form of "crowdfunding" (which corresponds to the meaning of "People will always meet each other somewhere"). The main motivation for this restart comes from the enthusiasm for exploring the unknown nature, the feelings for the alma mater of PKU, and the friendship and trust. All the participants this time contributed their efforts voluntarily. Prof. Hong-Wei Hou laboratory of the Institute of Hydrobiology of CAS provided sequencing materials; Dr. Feng Li (former PhD student in Shu-Nong Bai Lab at PKU) led the RDFZ (the High School Affiliated to Renmin University of China) students to establish a microfluidic culture system for Wolffia with the help of Prof. Chunxiong Luo's lab, and successfully induced the flowering of Wolffia under the stable laboratory conditions; Dr. Feng Li cooperated with the team of Dr. Yi-Qun Liu of the Experimental Instrument Center of SLS of PKU, and with the help of RDFZ students, completed a detailed description of the morphological construction of Wolffia; Mr. De-Peng Wang, the co-founder and CEO of Grandomics, generously offered free sequencing of the Wolffia genome, and completed the genome assembly analysis and other genomic analysis with Prof. Ling Li's lab at the Mississippi State University; Prof. Zhu-Kuan Cheng at the Institute of Genetics and Development of CAS determined the chromosome number of Wolffia; Prof. Fu-Chou Tang’s lab (SLS and BIOPIC, PKU) completed RNA-Seq of single Wolffia plantlet. Prof. Yi-Hua Zhou’s lab at the Institute of Genetics and Development of CAS completed the analysis of Wolffia vascular development and the functional verification of related genes; Dr. Huan Liu's team (BGI) completed the first single-cell RNA-seq of Wolffia; Prof. Xiao-Dong Su Lab at the SLS of PKU completed the protein structure prediction of unique Wolffia genes; Prof. Ge Gao Lab (BIOPIC, PKU) performed network structure analysis on the expression profile data related to flowering induction and constructed this website (Wolffiapond.net). All these works were done by amateurs or professional researchers in their spare time without any special funding support. The results of this "crowdfunding" research have been published on PNAS Nexus with the title of “The Plant-on-Chip: Core Morphogenesis Process in the Tiny Plant Woffila australiana”. All relevant data are deposited in this website. We hope that in the future, more people interested in exploring the basic principles of plant morphology will be inspired by the information on this website and join in the renaissance of plant science in the future.
References:
- Bai, S. (1999) Phenomena, interpretation of the phenomena and the developmental unit in plants. in Advances of Botany, Vol II, 52-69, ed. Li, Chensheng. Higher Education Publish House, Beijing (in Chinese)
- Bai SN (2019) Plant Morphogenesis 123: A Renaissance in Modern Botany? Sci. China Life Sci.
微萍(Woffila australiana)属于天南星科(Araceae)浮萍亚科(Lemnaceae),是世界上体积最小、形态结构最简单的被子植物。其椭球形小植株的形态结构可以用“四个1”来概括:长短和直径约1mm、1片叶(尽管其叶腋中包裹有生长点和分枝)、开花时通常只有1个雄蕊和1个雌蕊。
浮萍这类植物在中国的记载可以追溯到春秋战国时代。人们根据其生长特点而赋名:“無根而浮,常與水平,故曰苹也”。古人已经意识到浮萍类植物快速产生新个体的特性:“萍善滋生,一夜七子”。但关于浮萍起源,有人曾提出过杨树花落入水中变为浮萍的浪漫想像(世說楊華入水化爲浮萍)。文人常以浮萍无根、随波逐流而类比人生的不确定性:“一葉浮萍歸大海,人生何處不相逢”。
在现代科学领域内,曾经出现过两次有关浮萍的研究热潮。第一次以瑞士植物学家Elias Landolt为代表,从1950年代开始,搜集、保存浮萍(包括微萍)种质资源超过1000种,对浮萍的形态特征进行了详细的描述。美国植物生理学家William Hillman则试图把浮萍作为研究植物生理生化的模式生物。第二次则以美国分子生物学家Eric Lam为代表,希望借浮萍类植物快速生长的优势,将其发展成为生物反应器。此次热潮中参与的科学家人数增加,也实现了对几个浮萍(包括微萍)物种的基因组测序和转基因技术建立。
本网站建立的初衷与上述两次研究热潮有所不同,我们希望在本团队所获取研究发现的基础上搭建一个数据共享平台,使之成为有志于探索植物形态建成基本原理同道的交流空间。
本团队有关微萍的研究可以追溯到1994年。当时,刚从伯克利大学结束其博士后训练的白书农博士向他当年在中科院植物所读博士时的同窗好友张大明博士介绍“植物发育单位”概念时,张大明博士提出微萍可以作为检验“植物发育单位”概念的实验系统,并率先开始了把微萍建立为模式植物的新的尝试。几年后,他带领学生完成了中国微萍种质资源搜集与实验室无菌培养保存的工作。但他的努力因在北京的实验室中无法实现开花诱导而难以为继。
看到好友的尝试陷入困境,已入职北京大学工作的白书农博士因参加北京大学理论生物学中心(后改为定量生物学中心)的活动,有机会结识当时刚刚兴起的微流技术的领军人物,法国巴黎高师的陈勇教授,了解到微流技术在高通量优化培养条件上的潜在优势,就向中心同行提出将微流“扩容”为“毫流”,用来优化微萍开花诱导条件。于是”plant-on-chip“概念在定量生物学中心应运而生。相关实验也于2007年在物理学院欧阳颀教授和罗春雄博士的合作下在白书农实验室启动。可惜,此次尝试虽然让人获得很多有关微萍的第一手知识,但因各种阴差阳错,到2010年也功败垂成。
在2013年前后,中科院水生所的侯宏伟教授因人在武汉的“地利”(微萍在武汉植物园的水体中可以每年开花)加入微萍研究队伍。张大明老师将其多年精心采集的微萍样品悉数馈赠于他。
时间到了2016年,在各种机缘巧合之下,微萍研究又以“众筹”的形式(正应了“人生何处不相逢”之意)重现江湖。这次重启主要动力源自对探索未知自然的热情、对北大的母校情怀和朋友之间的友谊与信任。这次的所有参与者均是无偿自愿加入。中科院水生所的侯宏伟实验室提供测序材料;人大附中的李峰博士(毕业于北京大学白书农实验室)带领中学生,在北京大学定量中心罗春雄教授实验室的帮助下建立了微萍的微流培养体系,并成功实现在实验室条件下稳定诱导微萍开花;李峰博士和北京大学生命科学学院实验仪器中心刘轶群博士团队合作,在中学生的帮助下,完成了微萍形态建成过程的详细描述;武汉希望/未来组公司汪德鹏慷慨提供了微萍基因组免费测序,和美国密西西比州立大学的李灵教授实验室一起完成了基因组组装分析以及相关分析;中科院遗传发育所程祝宽教授实验室确定了微萍染色体数目;北京大学BIOPIC汤富酬教授实验室完成了单个微萍小植株表达谱测定;中科院遗传发育所周奕华教授实验室完成了微萍维管发育的分析与相关基因的功能验证;华大基因刘欢博士团队完成了微萍单细胞数据的采集与初步分析;北京大学生命科学学院苏晓东实验室完成了微萍特有基因序列的蛋白结构预测;北京大学BIOPIC高歌教授实验室对开花诱导相关的表达谱数据进行了网络结构分析,并建设了这个微萍相关研究信息的网站(Wolffiapond.net)。所有这些工作都是在没有任何专项经费支持的条件下,由业余爱好者或者专业研究人员业余时间完成的。上述“众筹”研究的结果已经以“The Plant-on-Chip: Core Morphogenesis Process in the Tiny Plant Woffila australiana”为题,于2023年4月19日在PNAS Nexus上在线发表。所有相关数据都保留在本网站中。希望将来有更多对植物形态建成基本原理有探索兴趣的人能从本网站的信息中获得启发和灵感,加入探索之中,成为植物科学复兴大业的创业者。
参考文献:
- 白书农(1999)现象,对现象的解释和植物发育单位。 李承森主编,『植物科学进展』(第二卷),52-69页,高等教育出版社,北京
- Bai SN (2019) Plant Morphogenesis 123: A Renaissance in Modern Botany? Sci. China Life Sci.