Chloroplast development involves changes in the stability of specific plast
id mRNAs. To understand how the half-lives of these mRNAs are modified, sev
eral laboratories are investigating how plastid mRNAs are degraded. This ha
s led to the isolation of a high-molecular-weight complex that contains an
endoribonuclease and a 3'-5' exoribonuclease, and the discovery that effici
ent mRNA degradation requires polyadenylation. These findings are similar t
o recent discoveries in Escherichia coli. However, an important difference
between the two systems is that chloroplast mRNA degradation involves nucle
ar-encoded proteins, Modification of these proteins could provide the mecha
nism for altering plastid-mRNA half-lives in response to developmental stim
uli.