Lipids Mediate Arbuscule Development and Senescence in Tomato Roots Colonized by Arbuscular Mycorrhizae Fungus under Drought Stress

Arbuscular mycorrhizae (AM) symbiosis can enhance plant resistance to drought stress (DS). This study aimed to investigate the DS effects on lipids at different stages of symbiosis and to link lipid profiles to arbuscule dynamics in tomato roots colonized by AM fungi. DS increased mycorrhizal colonization and arbuscule abundance at an early stage but decreased them at a later stage, delayed arbuscule development, and accelerated arbuscule senescence at a later stage. DS decreased the contents of phospholipids (PLs) and saturated neutral lipids (NLs) at the early stage but increased the contents of saturated PLs and unsaturated NLs at the late stage. Specifically, DS inhibited AM-specific PL contents but increased AM-specific NL contents, which was supported by the expression of <i>RAM</i>2, <i>STR</i>/<i>STR</i>2. These data indicate the negative effect of DS on AM symbiosis and arbuscule dynamics with the effect size depending on the symbiosis stage, which highlights the importance of the symbiosis stage under abiotic stress.