The chloroplast affects the transcription of a nuclear gene family

Abstract

Carotenoid deficient, maize seedlings ordinarily incur extensive photooxidative damage to their chloroplasts. This damage can be minimized by growing seedlings in very dim light. Cytosolic mRNA encoding a prevalent chloroplast protein, the light-harvesting chlorophyll a/b protein (LHCP), accumulates under low-intensity light, but rapidly disappears when plants are exposed to higher intensity light. Transcription studies were performed in vitro on nuclei isolated from carotenoid deficient seedlings grown first in low-intensity light and then transferred to higher intensity light. The rate of LHCP gene transcription was rapidly reduced in high intensity light. We propose that a signal of chloroplast origin is a necessary component of optimal transcription of LHCP genes and other nuclear genes encoding chloroplast proteins. Our data indicate that the signal originates at an early stage of chloroplast development, is continuously required, for LHCP gene transcription and has a short half-life. Photooxidative damage to the chloroplast destroys its capacity for further synthesis of the signal. A significant diurnal fluctuation in LHCP transcriptional activity was also observed.