Orthogonal Degron System for Controlled Protein Degradation in Cyanobacteria

Synechococcus elongatus PCC 7942 is a model cyanobacterium
for study of the circadian clock, photosynthesis, and bioproduction
of chemicals, yet nearly 40% of its gene identities and functions
remain unknown, in part due to limitations of the existing genetic
toolkit. While classical techniques for the study of genes (e.g., deletion or mutagenesis) can yield valuable information
about the absence of a gene and its associated protein, there are
limits to these approaches, particularly in the study of essential
genes. Herein, we developed a tool for inducible degradation of target
proteins in S. elongatus by adapting a method
using degron tags from the Mesoplasma florum transfer-mRNA
(tmRNA) system. We observed that M. florum lon
protease can rapidly degrade exogenous and native proteins tagged
with the cognate sequence within hours of induction. We used this
system to inducibly degrade the essential cell division factor, FtsZ,
as well as shell protein components of the carboxysome. Our results
have implications for carboxysome biogenesis and the rate of carboxysome
turnover during cell growth. Lon protease control of proteins offers
an alternative approach for the study of essential proteins and protein
dynamics in cyanobacteria.