Seed and organ size in plant is central to many aspects of evolutionary fitness and is also an important trait for agricultural purposes. However, the genetic and molecular mechanisms that control seed and organ size are poorly understood.
A recent study by Dr. LI Yunhai’s group at the Institute of Genetics and Developmental Biology, Chinese Academy of Sciences (CAS), in collaboration with Dr. Michael W. Bevan’s group at John Innes Centre, Dr. Dirk Inze’s group at Ghent University and Dr. Nico Dissmeyer’s group at Leibniz Institute of Plant Biochemistry revealed a novel mechanism that ubiquitylation activates DA1 peptidase to cleave and destabilize diverse growth regulatory proteins to control seed and organ size.
Previously, researchers from Dr. LI’s group identified the ubiquitin receptor DA1 as a central regulator in seed and organ size control. DA1 functions synergistically with E3 ubiquitin ligases DA2 and BIG BROTHER (BB)/ENHANCER OF DA1 (EOD1) to restrict seed and organ growth, suggesting that DA1 might share common downstream targets with DA2 and EOD1. Independently, DA1 interacts with UBIQUITIN-SPECIFIC PROTEASE15 (UBP15) and modulates UBP15 stability to control seed and organ growth.
In the latest study, they found that DA1 is ubiquitylated and activated by two RING E3 ligases, BB/EOD1 and DA2, which are subsequently cleaved by the activated peptidase and destabilized. DA1 peptidase activity also cleaves the deubiquitylase UBP15, which promotes cell proliferation, and the transcription factors TEOSINTE BRANCED 1/CYCLOIDEA/ PCF 15 (TCP15) and TCP22, which promote cell proliferation and repress endoreduplication.
These findings suggest a mechanism in which DA1 peptidase, activated transiently by BB or DA2, regulates the duration of cell proliferation and the transition to endoreduplication and differentiation during organ growth by coordinating the destabilization of diverse target regulatory proteins.
This work entitled " Ubiquitylation activates a peptidase that promotes cleavage and destabilization of its activating E3 ligases and diverse growth regulatory proteins to limit cell proliferation in Arabidopsis " was published in Genes & Development (doi:10.1101/gad.292235.116).
Figure. A model of the proposed transient mechanism of DA1 peptidase activation and the consequences of DA1-mediated cleavage of growth regulators during organ growth.