The present invention discloses the polynucleotide sequences of genes encoding aspartate transaminase (AAT) from Nicotiana tabacum and the modulation of their expression. There is described a plant cell comprising: (i) a polynucleotide comprising, consisting or consisting essentially of a sequence having at least 80% sequence identity to SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13 or SEQ ID NO: 15； (ii) a polypeptide encoded by the polynucleotide set forth in (i)； (iii) a polypeptide comprising, consisting or consisting essentially of a sequence having at least 95% sequence identity to SEQ ID NO: 6 or SEQ ID No: 8, at least 93% sequence identity to SEQ ID NO: 2 or SEQ ID NO: 10 or SEQ ID No: 12, or at least 94% sequence identity to SEQ ID NO: 4 or SEQ ID NO: 14 or SEQ ID NO: 16； or (iv) a construct, vector or expression vector comprising the isolated polynucleotide set forth in (i), wherein said plant cell comprises at least one modification which modulates the expression or activity of the polynucleotide or the polypeptide as compared to a control plant cell in which the expression or activity of the polynucleotide or polypeptide has not been modified.La présente invention concerne les séquences polynucléotidiques de gènes codant pour l'aspartate transaminase (AAT) provenant de Nicotiana tabacum ainsi que la modulation de leur expression. L'invention concerne une cellule végétale comprenant : (i) un polynucléotide comprenant, constitué ou essentiellement constitué d'une séquence présentant une identité de séquence d'au moins 80 % avec SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO: 7, SEQ ID NO: 9, SEQ ID NO: 11, SEQ ID NO: 13 ou SEQ ID NO: 15； (ii) un polypeptide codé par le polynucléotide décrit en (i)； (iii) un polypeptide comprenant, constitué ou essentiellement constitué d'une séquence présentant une identité de séquence d'au moins 95 % avec SEQ ID NO: 6 ou SEQ ID NO: 8, une identité de séquence d'au
