A branched-chain aminotransferase may regulate hormone levels by affecting KNOX genes in plants.
Branched-chain amino acid transaminases (BCATs) play a crucial role in the metabolic pathway of leucine, isoleucine and valine by catalyzing the last step of synthesis and/or the initial step of degradation of these amino acids. In this study, we characterized a new BCAT from Nicotiana benthamiana (NbBCAT, GeneBank accession No. EU194916), the deduced amino acid sequence of which exhibits a very high percentage of identity to the homologous enzymes from Solanum tuberosum (StBCAT-2, 91.5%) and Arabidopsis thaliana (AtBCAT1-6, 56.4-68.6%). Complementation experiment using a Deltabat1/Deltabat2 double knockout yeast strain system demonstrated enzymatic activities for NbBCAT. Ectopically expressed NbBCAT::green fluorescence fusion protein was targeted predominantly to the chloroplasts in tobacco protoplasts. The highest levels of NbBCAT transcripts were found in open flowers as well as in young leaves. Virus-induced gene silencing of NbBCAT resulted in abnormal leaf development and loss of apical dominance. In NbBCAT-silenced plants, two KNOTTED1-type genes, NTH15 and NTH23, were upregulated. This was accompanied by various hormone changes, as a result of transcriptional regulation of gibberellin 20-oxidase (Ntc12) and adenosine phosphate isopentenyltransferase. The transcript levels of NbBCAT could also be repressed by hormone treatment. These results suggest that NbBCAT, an enzyme in the branched-chain amino acid metabolic pathway, may be involved in the regulation of endogenous hormones by its effect on KNOX genes.
Gao
Feng
F
Peking-Yale Joint Center for Plant Molecular Genetics and Agrobiotechnology, The National Laboratory of Protein Engineering and Plant Genetic Engineering, National Center for Plant Gene Research (Beijing), College of Life Sciences, Peking University, 100871 Beijing, China.
Wang
Chunzheng
C
Wei
Chunhong
C
Li
Yi
Y
D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000187:drug effects / Q000201:enzymology / Q000235:genetics; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D020868:Gene Silencing / Q000187:drug effects; D017343:Genes, Plant; D005816:Genetic Complementation Test; D018398:Homeodomain Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009928:Organ Specificity / Q000187:drug effects; D010641:Phenotype; D010937:Plant Growth Regulators / Q000378:metabolism* / Q000494:pharmacology; D018515:Plant Leaves / Q000235:genetics / Q000254:growth & development; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D010942:Plant Viruses / Q000235:genetics; D021381:Protein Transport / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D013347:Subcellular Fractions / Q000187:drug effects / Q000201:enzymology; D014026:Nicotiana / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D000637:Transaminases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects
D018076:DNA, Complementary; D018398:Homeodomain Proteins; D010937:Plant Growth Regulators; D010940:Plant Proteins; D012333:RNA, Messenger; D000637:Transaminases; C019798:branched-chain-amino-acid transaminase