ABSTRACT: Amino acids (AA) are essential molecules for life because they are precursors for the synthesis of proteins and other organic compounds. Their metabolism in plants involves more than one cellular compartment, among which the chloroplast plays a key role. From the 20 essential AA, ten (Arg, Lys, Thr, Leu, Ile, Val, Trp, Phe, Tyr and His) are only synthesized in the plastids and seven (Asp, Cys, Gln, Glu, Gly, Ser and Met) can be synthesized in both chloroplast and other parts of the cell. Despite knowing the roles of AA in plant physiology, little has been assessed in plants with albino phenotypes, lacking chloroplasts. To assess the effect of chloroplast biogenesis disturbances on AA metabolism in albino and variegated somaclonal variations of Agave angustifolia Haw., a comparative proteomic based TMT- synchronous precursor selection (SPS)-MS3 strategy was used to determine the status of AA biosynthetic pathways. Besides the 20 essential AA was quantified to underpin proteomics finding. A total of 2,442 different proteins were identified in the proteome of the somaclonal variants, from which 82 correspond to enzymes participating in AA biosynthesis. From these 82, 32 proteins were differentially accumulated. On the other hand, the concentration of 16 and 12 of the AA synthesized by the chloroplast were over-accumulated in the variegated and albino somaclonal variant, respectively. In plantlets devoid of functional chloroplasts, there is a surprising increase of AA and key enzymes of the AA biosyntethic pathways, compared to green plantlets. This could suggest que la activation of AA biosynthesis is key to sustaining albino and variegated plantlets survival that lack chloroplasts.
Miguel Elizalde 