A research conducted at the Institute of Genetics and Development Biology of
the Chinese Academy of Sciences (CAS) led by Zhou Jianmin has discovered how
plants use a sophisticated mechanism to accurately control immune responses.
The research team previously found that a protein kinase called BIK1 is a
central player that relays signals from multiple immune receptors to
different cellular defenses. BIK1 is a rate-limiting component, whose
phosphorylation and accumulation are central to immune signal propagation.
In the study, they show that a pair of ubiquitin E3 ligases, PUB25 and
PUB26, that are responsible for adding poly-ubiquitin chains to BIK1, and
both CPK28 and the heterotrimeric G proteins regulate BIK1 stability through
PUB25/26. In the resting state, the immune receptors and BIK1 are not
activated, and plant immunity is regulated as heterotrimeric G proteins that
directly inhibit PUB25/26 E3 activity to stabilize BIK1.