Fig. 3.

Seed storage protein processing in Arabidopsis seedlings. Comparative N terminome analysis of 2.5-day old Arabidopsis VPE0 quadruple mutants and WT seedlings. A, Volcano plot of four biological replicate experiments with three pooled seedlings per genotype. Circle, dimethylated N termini; triangle, acetylated N termini; light blue/orange, significantly less/more abundant (p value <0.05 with log₂(VPE0/WT)<−1 or >1) N-terminal peptides matching known or predicted protein N termini; dark blue/dark red, significantly less/more abundant (p value <0.05, log₂<−1 or >1) neo-N termini matching “unexpected” positions within the protein models. B, Protein N termini derived from 12S seed storage proteins with reduced abundance in the VPE deficient mutant. Cleavage sites previously identified by Edmann sequencing are highlighted in yellow. C, iceLogo representing 24 cleavage sites deduced from 47 unexpected neo-N-terminal peptides that are significantly more abundant in wt, filtered for redundancy created by exopeptidase ragging. Dashed line indicates cleavage site.