The biosynthetic gene cluter and proposed biosynthetic pathways for PLYA. A, Organization of the genes for the biosynthesis of PLYA. Their putative functions were indicated by color-labeling. B, the proposed model for PLYA skeleton assembly driven by the hybrid PKS/NRPS system. KS: Ketosynthase; AT: Acyltransferase; ACP: Acyl carrier protein; DH: Dehydratase; KR: Ketoreductase; ER: Enoyl reductase; A: Adenylation domain; PCP: Peptidyl carrier protein; C: Condensation domain; E: Epimerase domain; M: Methyltransferase; TE: Thioesterase. C, the proposed pathway for the biosynthesis of 3 (2-(2-methylbutyl)malonyl-ACP). D, the biosynthesis of 4 (l-piperazic acid). E, the proposed pathway for the biosynthesis of the building blocks 5 (N-hydroxylvaline) and 6 (N-hydroxylalanine). F and G, the proposed biosynthetic pathways of the building blocks 7 ((R)-3-hydroxy-3-methyproline) and 8 (3-hydroxyleucine).