Summary Enhancing lipid accumulation by redirecting carbon from starch to triacylglycerol (TAG) in vegetative tissues is a promising strategy for developing high‐energy‐density crops for bioenergy production. However, our understanding of how starch and TAG metabolism interact and how this interaction affects growth and photosynthesis is incomplete. Here, we investigated the metabolic and physiological consequences of disrupting starch biosynthesis and TAG turnover in Arabidopsis thaliana by generating single, double, and triple mutants involving ADG1 (starch biosynthesis), TGD1 (lipid trafficking), and SDP1 (TAG lipase). Unexpectedly, elimination of starch biosynthesis lowered TAG levels in the high‐TAG‐accumulating tgd1 mutant, primarily through enhanced TAG breakdown. This decline was completely reversed by sucrose supplementation, suggesting that TAG degradation was induced by carbon limitation. Genetic suppression of TAG turnover via SDP1 disruption in the starchless tgd1 adg1‐1 background led to a nine‐fold rise in leaf TAG accumulation in the tgd1 sdp1 adg1‐1 triple mutant, together with enhanced photosynthetic performance. However, this metabolic reprogramming incurred growth penalties. Our results highlight the role of dynamic TAG turnover in maintaining metabolic balance and photosynthesis in starch‐deficient backgrounds. These findings underscore the need for refined metabolic engineering strategies that coordinate TAG biosynthesis and degradation to optimize lipid accumulation in bioenergy crops.
Fan et al. (Sun,) studied this question.