Angelovici Ruthie, Lipka Alexander E, Deason Nicholas, Gonzalez-Jorge Sabrina, Lin Haining, Cepela Jason, Buell Robin, Gore Michael A, Dellapenna Dean
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, Michigan 48824-1319.
Plant Cell. 2013 Dec;25(12):4827-43. doi: 10.1105/tpc.113.119370. Epub 2013 Dec 24.
Branched-chain amino acids (BCAAs) are three of the nine essential amino acids in human and animal diets and are important for numerous processes in development and growth. However, seed BCAA levels in major crops are insufficient to meet dietary requirements, making genetic improvement for increased and balanced seed BCAAs an important nutritional target. Addressing this issue requires a better understanding of the genetics underlying seed BCAA content and composition. Here, a genome-wide association study and haplotype analysis for seed BCAA traits in Arabidopsis thaliana revealed a strong association with a chromosomal interval containing two branched-chain amino acid transferases, BCAT1 and BCAT2. Linkage analysis, reverse genetic approaches, and molecular complementation analysis demonstrated that allelic variation at BCAT2 is responsible for the natural variation of seed BCAAs in this interval. Complementation analysis of a bcat2 null mutant with two significantly different alleles from accessions Bayreuth-0 and Shahdara is consistent with BCAT2 contributing to natural variation in BCAA levels, glutamate recycling, and free amino acid homeostasis in seeds in an allele-dependent manner. The seed-specific phenotype of bcat2 null alleles, its strong transcription induction during late seed development, and its subcellular localization to the mitochondria are consistent with a unique, catabolic role for BCAT2 in BCAA metabolism in seeds.
支链氨基酸（BCAAs）是人类和动物饮食中九种必需氨基酸中的三种，对发育和生长中的众多过程都很重要。然而，主要作物种子中的BCAA水平不足以满足饮食需求，因此通过基因改良提高种子中BCAA的含量并使其平衡成为一个重要的营养目标。要解决这个问题，需要更好地了解种子BCAA含量和组成的遗传学基础。在这里，一项针对拟南芥种子BCAA性状的全基因组关联研究和单倍型分析揭示了与一个染色体区间的强烈关联，该区间包含两个支链氨基酸转移酶BCAT1和BCAT2。连锁分析、反向遗传学方法和分子互补分析表明，BCAT2的等位基因变异是该区间种子BCAAs自然变异的原因。用来自拜罗伊特-0和沙赫达拉两个显著不同等位基因对bcat2无效突变体进行互补分析，结果表明BCAT2以等位基因依赖的方式影响种子中BCAA水平、谷氨酸循环和游离氨基酸稳态的自然变异。bcat2无效等位基因的种子特异性表型、其在种子发育后期的强烈转录诱导以及其在线粒体中的亚细胞定位，都与BCAT2在种子BCAA代谢中独特的分解代谢作用一致。
