The central role of acetyl-CoA in plant metabolism, as examined through studies of ATP citrate lyase and the bio1 mutant of Arabidopsis

The acetyl-CoA/biotin network encompasses acetyl-CoA generation and utilization, biotin synthesis, recovery, and transport, and myriad metabolic processes requiring biotin-containing enzymes. To expand understanding of this network and its control, plants with altered levels of ACL (ATP citrate lyase) and BIO1 (adenosylmethionine-8-amino-7-oxononanoate synthase) were examined.; An inducible promoter provides a powerful method to test the effects of altered expression of specific genes. The synthetic GVG promoter, reported to be sterol-inducible in Arabidopsis thaliana, was inducible in Glycine max (soybean) when used to control the GUS reporter gene, or the ACLA or ACLB genes. It showed the same unique pattern in soybean and Arabidopsis, directing expression primarily to vasculature of leaves and roots.; ACL is a heteromeric enzyme, responsible for production of cytosolic acetyl-CoA. Over-expression of the ACLA-1 and ACLB-2 genes individually in Arabidopsis under the control of the GVG promoter led to significantly increased ACLA and ACLB RNA accumulation. Over-expressing one subunit of ACL had no effect on mRNA level of the other subunit or ACL enzyme activity. Crossing transgenic lines over-expressing high levels of ACLA and ACLB RNA yielded plants containing both transgenes. ACLA and ACLB RNA levels were greatly increased in ACLA + ACLB plants, yet ACLA and ACLB protein levels, ACL enzyme activity, and phenotype were similar to the wild-type. However, cold treatment increased ACL activity by approximately 1.5-fold in ACLA + ACLB plants compared to wild-type plants. These data suggest that ACL is regulated at the translational and/or post-translational levels, and its regulation can be modulated environmentally.; Global transcript profiling experiments utilizing the Arabidopsis bio1 mutant deficient in biotin synthesis reveal decreased accumulation of RNAs encoding processes directly related to the biotin network in bio1 plants, including subunits of acetyl-CoA carboxylase and methylcrotonyl-CoA carboxylase, and L-allo-threonine aldolase/lyase. Several mRNAs involved in defense and stress responses and secondary metabolism show increased accumulation in bio1 mutants when compared to the wild-type plants. At the same time, there are decreases in particular mRNAs in photosynthesis and the TCA cycle. Exogenous biotin caused changes in mRNA profiles in both the bio1 and wild-type plants.