Control of organ size by cell proliferation and cell expansion is a fundamental developmental process, but the mechanisms that establish the final size of organs and whole organisms remain elusive in plants and animals.
Dr. LI Yunhai’s group from the Institute of Genetics and Developmental Biology, the Chinese Academy of Sciences has previously demonstrated that gene DA1, which encodes a predicted ubiquitin receptor, controls the final size of seeds and organs by restricting cell proliferation in Arabidopsis. Through a genetic screen for mutations that enhance the floral organ size of da1-1, scientists in LI Yunhai’ group have identified an enhancer of da1-1 (eod8-1). The eod8-1 mutation was identified in Mediator complex subunit 25 (MED25), which is involved in the transcriptional regulation of gene expression. Loss-of-function mutations in MED25 form large organs, they report, whereas plants overexpressing MED25 have small organs. These alterations in organ size are caused by changes in both cell number and cell size. Genetic analyses show that MED25 functions redundantly with DA1 to control organ growth by restricting cell proliferation. These findings show that MED25 plays a crucial role in setting final organ size, suggesting an important point of regulation in plant organ size control within the transcriptional machinery and also suggesting this pathway as a target for biomass production.
This work with XU Ran as the first author has been online published on Development (DOI:10.1242/dev.071423). This research was supported by the National Basic Research Program of China and National Natural Science Foundation of China.
AUTHOR CONTACT:
LI Yunhai, Ph.D.
Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, China.
(Image by XU Ran Xu and LI Yunhai)
Figure. Genetic interaction between med25-2 and da1-1
(A-D) Flowers of Col-0, med25-2, da1-1 and med25-2 da1-1 double mutant in Arabidopsis. (E) Petal area of Col-0, med25-2, da1-1 and med25-2 da1-1 double mutant. (F) The epidermal cell area on the adaxial side of Col-0, med25-2, da1-1 and med25-2 da1-1 petals. (G) The epidermal cell number on the adaxial side of Col-0, med25-2, da1-1 and med25-2 da1-1 petals. Mean ± s.d. relative to the respective wild-type values. Scale bars: 1mm.
