In more than four decades, from admission to Anhui Agricultural College to retirement from the School of Life Science in Peking University, Dr. Shu-Nong Bai mainly worked in the field of plant biology. He has exposed to relatively a large spectrum of phenomena in plant development. He has investigated the mechanism of heterosis in rice during his MS program, the photoperiodic effects upon rice male fertility during his PhD program, apomixes and Arabidopsis emf mutant during his postdoc. After moved to PKU, he has carried out investigation projects on the regulatory mechanisms of cucumber unisexual flower development, of stamen early development and chromosomal regulatory mechanism upon root epidermal cellular patterning. Based on the empirical experiences, he has proposed the concepts of “plant developmental unit” in 1993, “sexual reproduction cycle” in 2011, “plant developmental program” in 2013; and in 2016, integrated all these into a hypothesis “plant morphogenesis 123”. In 2023, under a “crowd-funding” mode, his friends and him developed an experimental system with Wolffia australiana, enabled the virtual concept of “plant developmental unit” into a real plantlet. In his efforts attempting to understand the underlying mechanism of plant developmental phenomena, he had also tried to understand the essences of life, education, as well as the purpose of undergraduate education in life science. Currently, he still delivers a class called “Logic of Life” in Summer School of PKU.

Ph.D., Plant physiology, Institute of Botany, CAS, 1990
MS, Plant physiology, Wuhan University, 1986
BA, Agronomy, Anhui Agricultural College, 1982

1998-2021 Professor, College of Life Sciences, Peking University
1997-1998 Research Associate, Plant development, University of California at Berkeley
1996-1998 Professor, Institute of Botany, CAS
1994-1996 Associate professor, Institute of Botany, CAS
1990-1994 Assistant professor, Institute of Botany, CAS
1991-1994 Postdoctoral fellow, Department of Plant Biology, UCB, with Z. R. Sung
1987-1990 Graduate student for PhD degree, Institute of Botany, CAS
1986-1987 Education strategist, participated in the establishment of Hefei Institute of Economy and Technology, sponsored by the Chinese National Tobacco Corporation
1983-1986 Graduate student for MS degree, Wuhan University
1982-1983 Junior Scientist, Huaibei Seed Corporation

2002 NSFC panelist in developmental biology
1997-2000 Member of Steering committee for the MST program of “Molecular Mechanism of Sexual Reproduction in Higher Plants”
1994-1995 CAS panelist of the panel of strategy research for the development of biology in CAS

2015 The most popular teacher in the School of Life Sciences of the year
2010 The most popular teacher in the School of Life Sciences of the year
2009 Excellence Award of Academician Yang Fuqin and Wang Yangyuan
2006 Dongbao Awards for excellent teachers
1991-1993 The Rockefeller fellow of Rice Biotechnology Program

My independent scientific career started from an attempt to decipher genetic program of organ formation, using stamen as an experimental system. This effort led to a scenario that a stamen is a node of three cycles: cell cycle, sexual reproduction cycle and life cycle, functioning as a turning point linking multicellular structures and unicellular sexual reproduction cycle.

The rationale of choosing decipher genetic program of organ formation as a research interest could be traced back to my postdoc era in UC Berkeley with Renee Sung. Through a project characterizing an Arabidopsis mutant “embryonic flower” in Renee’s lab, I firstly faced a challenge on which the “vegetative” or “reproductive” phase is “default”, whether a plant has a developmental program, in comparison with animal individual, and if a plant has, when is its starting and ending point. To answer these questions, I proposed a new concept called “plant developmental unit (PDU)” in 1993 (Bai 1999; Bai and Xu 2013).

Two approaches were taken in understanding organ formation of stamen since 1998 when I moved to Peking University. One approach was to understand what happens to block stamen development in female flowers through investigation of unisexual flower development of cucumber. This approach led to a realization that the development of unisexual flower in mostly known monoecious and dioecious plants is not an issue of sex differentiation or determination, as people believed at least since 1933, but an issue of outcross promotion (Bai and Xu, 2013). To understand what sex differentiation is in plants, I first discovered a phenomenon called “sexual reproduction cycle (SRC)”, a modified cell cycle consisting of three events: meiosis, heterogametogenesis and fertilization (Bai 2015a), then realized that sex differentiation is a somatic differentiation occurring in multicellular organisms to ensure heterogametogenesis, such as gonad differentiation in animals. From this perspective, the process best fitting the definition in plants is the differentiation of antheridium and archegonium occurring in gametophytes of most mosses and ferns. These differentiations are therefore considered as “real sex differentiations” in plants. In contrast, in seed plants such as angiosperms, the differentiation of stamen and ovule occurring in sporophyte is evolutionarily derived from heterospory, not directly leading to heterogametogenesis, but borrowed to establish divergence point required for heterogametogenesis, such a differentiation should be therefore considered as “pseudo sex differentiation”.

While the clarification of the concept of sex differentiation in plants did not lead to a better access to the problem, discovery of SRC introduced some new perspectives in understanding some fundamental questions in biology. For example, the sexual reproduction is no longer a way of production, comparable to asexual reproduction, but an ultimate mechanism to adapt environmental changes. In addition, multicellular structures are interpolated into the SRC in either or both intervals from zygote to meiotic cells and from meiotically-produced cells to gametes (Bai 2015a).

Within the conceptual framework of SRC and inspired by experimental findings from others labs, our findings from the second approach led to raise of new concept of “plant developmental program (PDU)” (Bai, 2015b). Our second approach to decipher the genetic program of stamen organ formation is molecular description of early developmental process of rice stamen through gene expression profiling. We unexpectedly found that a previously annotated C-class MADS protein OsMADS58 can bind photosynthetic genes and inhibit their expression (Chen et al, 2015). Such a binding and inhibition affects chloroplast development, redox status and germ cell differentiation in rice stamen. To understand the significance, I realized that as photoautotrophic organisms, the first priority for plants should be to increase their photosynthetic surface. However, when photosynthetic surface increased, the internal and external stresses increase as well. These stresses finally compel the multicellular structure reduced and returned to unicellular SRC, the ultimate stress adaptation mechanism. When all land plants considered, such a process can occur not only in sporophyte, but also in gametophyte. From this perspective, the concept of “plant developmental program (PDP)” emerged: upon the backbone of SRC, multicellular structure interpolated for energy acquisition. Such interpolation drives the zygote-derived multicellular structure move away from SRC. Accompany with the increase of photosynthetic surface, the stresses increased, which opposes the trends of increase of photosynthetic surface. When the stresses become strong enough and dominant over the multicellular structures, somewhere the germ cells are induced and the whole process returned to SRC for adapting the stresses. The balance between the two driving forces of photoautotrophic and stress response determines the shape and functions of lateral organs and resulting in sequential change of organ types in PDU (Bai 2015b).

Since the SRC emerged before multicellular organisms, it is reasonable to believe that all three domains of multicellular organisms evolved from the interpolation to the SRC. Differences came from the way of energy acquisition. In animals, shortly after multicellularization, soma and germline are diverged. The former carried out the function of energy acquisition and environment adaptation and later functions as a major carrier of SRC. Thus, the animal developmental program presents in a dichotomous mode. In plants, as described above, two interpolations exist and therefore, the PDP presents in a “double-ring mode” (Bai 2015b).

Taken together, a set of principles emerged that governs plant morphogenesis or development although numerous variations can be added in for each species. These principles could be summarized as “plant morphogenesis 123” (Bai, 2019). ONE means one start point, i.e. SRC. TWO means two themes, i.e. structure building (through “neo-modularization`) and environment responding (through two driving forces, i.e. photoautotroph and stresses responses). THREE means three sequential steps to complete a single “ring”. I created a term “syllogoid (Syl- together, logo- reasoning, id- alike)” to describe such three steps:

1. Photoautotroph drives increase of surface for photosynthesis and away from SRC;
2. Increase of photosynthetic surface accompanies increase of external and internal stresses;
3. Increase of stresses reduces photosynthetic surface and compels the morphogenesis back to SRC.

Through the “plant morphogenesis 123”, a life cycle completed, a PDU formed and many of PDU consists of a colony that we see as a plant.

Based on the investigation of the regulatory mechanism of early stamen development. we finally realized that the stamen is not an “organ”, as previously understood, but a cluster of microsporangia. Along with the cellular differentiation after the cluster initiated, the diploid germ cells (DGC) were induced first along an auxin gradient, interacting with other genes (Zhao et al, 2017; Zheng et al, 2020). Then, the differentiation of the DGC recruits surrounding cells to differentiate as nursing and protecting cells. We proposed a “Two-way Induction” hypothesis to explain the process.

References

Bai SN (1999) Phenomena, interpretation of the phenomena and the developmental unit in plants. in Advances of Botany Vol II, ed. Li, Chensheng. 52-69, Higher Education Publish House, Beijing (in Chinese)
Bai SN (2015a) The concept of the sexual reproduction cycle and its evolutionary significance. Front. Plant Sci. 6:11.
Bai SN (2015b) Plant developmental program: Sexual reproduction cycle derived “double ring”. Sci. Sin Vitae 45 (9): 811-819 (in Chinese)
Bai SN (2019) Plant Morphogenesis 123: A Renaissance in Modern Botany? Sci. China Life Sci. 62(4):453-466.
Bai SN, Xu ZH (2013) Unisexual cucumber flowers, sex and sex differentiation. In Jeon K, Ed.: International Review of Cell and Molecular Biology, Vol 304, 1-56. UK: Academic Press
Chen R, Shen LP, Wang DH, Wang FG, Zeng HY, Chen ZS, Peng YB, Lin YN, Tang X, Deng MH, Yao N, Luo JC, Xu ZH, Bai SN (2015) A gene expression profiling of early rice stamen development that reveals inhibition of photosynthetic genes by OsMADS58. Mol. Plant 8：1069-1089
Zhao F, Zheng YF, Zeng T, Sun R, Yang JY, Li Y, Ren DT, Ma H, Xu ZH, Bai SN (2017) Phosphorylation of SPOROCYTELESS/NOZZLE by MPK3/6 is Required for Arabidopsis Anther Development. Plant Physiol. 173:2265-2277. DOI:10.1104/pp.16.01765
Zheng YF, Wang DH, Ye SD, Chen WQ, Li GL, Xu ZH, Bai SN, Zhao F (2021) Auxin guides germ-cell specification in Arabidopsis anthers. PNAS 118(22):e2101492118

Bai SN (2023) A Reconsideration of Sex: Heterogametogenesis, Sex Differentiation, and Sexual Behavior, from the Perspective of the Sexual Reproduction Cycle. In Ma and Xu ed. Regulation of Plant Development. Springer (in press)

Bai SN (2019) Plant Morphogenesis 123: A Renaissance in Modern Botany? Sci. China Life Sci. 62(4):453-466.

Bai SN, Ge H, Qian H (2018) Structure for Energy Cycle: A unique status of Second Law of Thermodynamics for living systems. Sci. China Life Sci. doi: 10.1007/s11427-018-9362-y

Bai SN (2016) Make a new cloth for a grown body: From plant developmental unit to plant developmental program. Annual Review of New Biology 2015: 73-116, Sci. Press, Beijing

Bai, S. N. (2015) The concept of the sexual reproduction cycle and its evolutionary significance. Frontiers in Plant Science 6:11. doi:10.3389/fpls.2015.00011

The Logic of Life (Undergraduates), Summer School, PKU