Flowering plants dominate the land environment on earth partly due to their unique reproduction mechanism. They produce flowers and bear their seeds in fruits. Compared with other plants characterized by single fertilization event, flowering plants evolved double fertilization by which the two fertilized female gametes, the egg cell and central cell, generates the embryo and endosperm, respectively, within the seeds. The endosperm, as a storage organ, nurtures the embryo during seed development and germination, and also serves as an important food source for human being. However, how the central cell is specified and evolved is still unknown.
Recently, a team led by Professors YANG Weicai and LI Hongju at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, revealed a transcriptional repression mechanism on how the central cell is specified.
The study found that the central cell-expressed transcription factor AGL80 functions to ensure its gametic fate through a transcription repression mechanism. When the gene is disrupted, the central cell switches to non-gametic fate and loses the fertilization ability by the sperm cell, thus only single fertilization of the egg occurs. The study also found that when AGL80 is expressed in the non-gametic cell, e.g. synergid cell, it can to some extent switch the synergid fate to a central cell fate.
Through genetic and biochemical analysis, it is found that in AGL80 sequence an EAR motif (LNLNLN), which has been suggested to coordinate the transcription repression machinery in other transcription factors, is essential for the function of AGL80.
Further, the research team also explored the origination of this molecular mechanism in diverse groups of plant taxa and found that it is conserved only in Brassicacea.
This study first established a transcriptional programing mechanism on how the central cell is specified and opened up the possible future direction for the study of the evolution of the central cell and double fertilization.
The study is published in PNAS entitled “Transcriptional repression specifies the central cell for double fertilization” (doi: 10.1038/s41477-020-0599-1) on March 4. ZHANG Mengxia and ZHU Shanshan are the first authors of the study, both of whom are graduated PhD of University of Chinese Academy of Sciences, YANG Weicai and LI Hongju are the corresponding authors. YANG is also doctoral supervisor at University of Chinese Academy of Sciences. ZHAO Yongchao (PhD student at University of Chinese Academy of Sciences, institute: Institute of Botany, CAS) and Prof. GUO Yalong at Institute of Botany, CAS, also contributed to the study.
Figure: The mechanism of AGL80 in central cell specification (Image by IGDB). Cc, central cell; ec, egg cell, ac, antipodal cell; sc, synergid cell. (Image by IGDB)
Source: Institute of Genetics and Developmental Biology, CAS
