Plastid acyl carrier proteins play redundant roles in seed oil accumulation with functional differentiation on the fatty acid flux.

Plastid ACPs are not limiting factors for seed oil accumulation and show functional redundancy, while their differentiation affects fatty acid composition. Plastid acyl carrier proteins (ACPs) act as acyl carriers in the fatty acid biosynthesis, yet the specific functions of different isoforms and their roles in seed oil accumulation remain unclear. To investigate the functions of the five ACPs in Arabidopsis seeds, this study analyzed their structure, expression pattern, and phenotypes of mutants and seed-specific overexpression lines. The results showed that ACP1, ACP2, ACP3, and ACP5 are expressed in developing seeds. Total fatty acid content of seeds is not affected by mutations of single, double, or triple ACPs, or their overexpression. Comprehensive analysis of changes in fatty acid composition in loss-of-function and overexpression seeds revealed that ACP1 and ACP5 may promote the accumulation of longer-chain and more unsaturated fatty acids. ACP2 has similar, but weaker effects on fatty acid composition compared with ACP1 and ACP5. ACP3 may uniquely enhance the accumulation of 20:1. ACP4 differs from the other four ACPs in both protein structure and a function of increasing 16:0 and 18:2. Our results indicate that ACPs exhibit functional redundancy and may not be limiting factors in oil accumulation, yet these ACPs differentially affect fatty acid composition.