College of Life Sciences, China Jiliang University, Hangzhou 310018, China.
Department of Botany and Plant Pathology, Purdue University, West Lafayette, IN 47907-2054, USA.
Plant Physiol. 2023 May 31;192(2):886-909. doi: 10.1093/plphys/kiad133.
Autophagy and multivesicular bodies (MVBs) represent 2 closely related lysosomal/vacuolar degradation pathways. In Arabidopsis (Arabidopsis thaliana), autophagy is stress-induced, with deficiency in autophagy causing strong defects in stress responses but limited effects on growth. LYST-INTERACTING PROTEIN 5 (LIP5) is a key regulator of stress-induced MVB biogenesis, and mutation of LIP5 also strongly compromises stress responses with little effect on growth in Arabidopsis. To determine the functional interactions of these 2 pathways in Arabidopsis, we generated mutations in both the LIP5 and AUTOPHAGY-RELATED PROTEIN (ATG) genes. atg5/lip5 and atg7/lip5 double mutants displayed strong synergistic phenotypes in fitness characterized by stunted growth, early senescence, reduced survival, and greatly diminished seed production under normal growth conditions. Transcriptome and metabolite analysis revealed that chloroplast sulfate assimilation was specifically downregulated at early seedling stages in the atg7/lip5 double mutant prior to the onset of visible phenotypes. Overexpression of adenosine 5'-phosphosulfate reductase 1, a key enzyme in sulfate assimilation, substantially improved the growth and fitness of the atg7/lip5 double mutant. Comparative multi-omic analysis further revealed that the atg7/lip5 double mutant was strongly compromised in other chloroplast functions including photosynthesis and primary carbon metabolism. Premature senescence and reduced survival of atg/lip5 double mutants were associated with increased accumulation of reactive oxygen species and overactivation of stress-associated programs. Blocking PHYTOALEXIN DEFICIENT 4 and salicylic acid signaling prevented early senescence and death of the atg7/lip5 double mutant. Thus, stress-responsive autophagy and MVB pathways play an important cooperative role in protecting essential chloroplast functions including sulfur assimilation under normal growth conditions to suppress salicylic-acid-dependent premature cell-death and promote plant growth and fitness.
自噬作用和多泡体（MVBs）代表 2 种密切相关的溶酶体/液泡降解途径。在拟南芥（Arabidopsis thaliana）中，自噬作用是应激诱导的，自噬作用的缺乏会导致应激反应的严重缺陷，但对生长的影响有限。LYST-INTERACTING PROTEIN 5（LIP5）是应激诱导的 MVB 生物发生的关键调节因子，LIP5 的突变也会强烈损害应激反应，而对拟南芥的生长影响很小。为了确定这 2 种途径在拟南芥中的功能相互作用，我们在 LIP5 和 AUTOPHAGY-RELATED PROTEIN（ATG）基因中都产生了突变。atg5/lip5 和 atg7/lip5 双突变体在适应性方面表现出强烈的协同表型，其特征是生长迟缓、早衰老、存活率降低和在正常生长条件下种子产量大大减少。转录组和代谢物分析表明，在 atg7/lip5 双突变体可见表型出现之前，早期幼苗阶段叶绿体硫酸盐同化特别下调。关键酶腺苷 5'-磷酸硫酸还原酶 1 的过表达大大改善了 atg7/lip5 双突变体的生长和适应性。比较多组学分析进一步表明，atg7/lip5 双突变体在其他叶绿体功能中受到强烈损害，包括光合作用和初级碳代谢。atg/lip5 双突变体的过早衰老和存活率降低与活性氧的积累增加和应激相关程序的过度激活有关。阻断 PHYTOALEXIN DEFICIENT 4 和水杨酸信号阻止了 atg7/lip5 双突变体的早期衰老和死亡。因此，应激反应性自噬作用和 MVB 途径在保护包括硫同化在内的基本叶绿体功能方面发挥着重要的协同作用，在正常生长条件下抑制水杨酸依赖的过早细胞死亡，促进植物生长和适应性。
