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Proc Natl Acad Sci U S A. 2019 May 14;116(20):10162-10167. doi: 10.1073/pnas.1820426116. Epub 2019 Apr 15.

GUN1 interacts with MORF2 to regulate plastid RNA editing during retrograde signaling.

Zhao X1,2, Huang J3,2, Chory J1,2.

Author information

1
Howard Hughes Medical Institute, Salk Institute for Biological Studies, La Jolla, CA 92037; xbzhao16@gmail.com chory@salk.edu.
2
Plant Biology Laboratory, Salk Institute for Biological Studies, La Jolla, CA 92037.
3
Howard Hughes Medical Institute, Salk Institute for Biological Studies, La Jolla, CA 92037.

Abstract

During development or under stress, chloroplasts generate signals that regulate the expression of a large number of nuclear genes, a process called retrograde signaling. GENOMES UNCOUPLED 1 (GUN1) is an important regulator of this pathway. In this study, we have discovered an unexpected role for GUN1 in plastid RNA editing, as gun1 mutations affect RNA-editing efficiency at multiple sites in plastids during retrograde signaling. GUN1 plays a direct role in RNA editing by physically interacting with MULTIPLE ORGANELLAR RNA EDITING FACTOR 2 (MORF2). MORF2 overexpression causes widespread RNA-editing changes and a strong genomes uncoupled (gun) molecular phenotype similar to gun1 MORF2 further interacts with RNA-editing site-specificity factors: ORGANELLE TRANSCRIPT PROCESSING 81 (OTP81), ORGANELLE TRANSCRIPT PROCESSING 84 (OTP84), and YELLOW SEEDLINGS 1 (YS1). We further show that otp81, otp84, and ys1 single mutants each exhibit a very weak gun phenotype, but combining the three mutations enhances the phenotype. Our study uncovers a role for GUN1 in the regulation of RNA-editing efficiency in damaged chloroplasts and suggests that MORF2 is involved in retrograde signaling.

KEYWORDS:

GUN1; MORF2/RIP2; PPR; RNA editing; retrograde signaling

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