Catabolism of Branched Chain Amino Acids Supports Respiration but Not Volatile Synthesis in Tomato Fruits

The branched-chain amino acid transaminases （BCATs） have a crucial role in metabolism of the branched-chain amino acids leucine, isoleucine, and valine. These enzymes catalyze the last step of synthesis and the initial step of degradation of these amino acids. Although the biosynthetic pathways of branched chain amino acids in plants have been extensively investigated and a number of genes have been characterized, their catabolism in plants is not yet completely understood. We previously characterized the branched chain amino acid transaminase gene family in tomato, revealing both the subcellular localization and kinetic properties of the enzymes encoded by six genes. Here, we examined possible functions of the enzymes during fruit development. We further characterized transgenic plants differing in the expression of branched chain amino acid transaminases I and 3, evaluating the rates of respiration in fruits deficient in BCAT1 and the levels of volatiles in lines overexpressing either BCAT1 or BCAT3. We qua