Differential regulation of mRNA levels of acyl carrier protein isoforms in Arabidopsis.

All higher plants express several different acyl carrier protein (ACP) isoforms in a tissue-specific manner. We provide evidence that expression of mRNA for the most abundant ACP isoform in Arabidopsis leaves (ACP4) is increased severalfold by light, whereas mRNA levels for ACP isoforms 2 and 3 are independent of light. The presence of GATA-like motifs in the upstream region of the Acl1.4 gene (encoding for ACP4) and the similarity in light-mediated induction to ferredoxin-A mRNA suggests a direct role of light in Acl1.4 gene activation. Polyribosomal analysis indicated that light also affects the association of ACP transcripts with polysomes, similarly to mRNAs encoding ferredoxin-A. ACP2, ACP3, and ACP4 mRNA levels were also examined in Arabidopsis cell suspension culture and were found to be differentially controlled by metabolic and/or growth derived signals. Comparison of 5'-untranslated regions (UTRs) of ACP mRNAs of diverse plant species revealed two motifs that have been conserved during evolution, a CTCCGCC box and C-T-rich sequences. Fusions of the 5'-UTR sequences of ACP1 and ACP2 to luciferase and expression in transgenic plants indicated that the ACP1 leader contributes to preferential expression in seeds, whereas the ACP2 5'-UTR favored expression in roots. The deletion of 58 bp containing the conserved motifs of the ACP1 5'-UTR resulted in 10- to 20-fold lower gene expression in leaf and seed tissues of transgenic Arabidopsis plants.