Sterols are essential lipids for plant growth, and the sterol content is tightly regulated by a fail-safe system consisting of two processes: 1) suppression of excess sterol production by a negative regulator of sterol biosynthesis (HIGR STEROL ESTER 1, HISE1), and 2) conversion of excess sterols to sterol esters by PHOSPHOLIPID STEROL ACYLTRANSFERASE 1 (PSAT1) in Arabidopsis thaliana. The hise1-3 psat1-2 double mutant has a 1.5-fold higher sterol content in leaves than the wild type; this upregulates the expression of stress-responsive genes, leading to disruption of cellular activities in leaves. However, the effects of excess sterols on seeds are largely unknown. Here, we show that excess sterols cause multiple defects in seeds. The seeds of hise1-3 psat1-2 plants had a higher sterol content than wild-type seeds and showed a deeper color than wild-type seeds because of the accumulation of proanthocyanidin. The seed coat in the hise1-3 psat1-2 mutant was abnormally wrinkled. Seed coat formation is accompanied by cell death-mediated shrinkage of the inner integument. In the hise1-3 psat1-2 mutant, transmission electron microscopy showed that shrinkage of the integument was impaired, resulting in a thick seed coat and delayed seed germination. Moreover, psat1-2 and hise1-3 psat1-2 seeds displayed defective imbibition. Taken together, the results suggest that excess sterols impair proper seed coat formation, thereby inhibiting seed germination.

中文翻译：

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过量的甾醇积累影响拟南芥种子形态和生理

甾醇是植物生长所必需的脂质，甾醇含量受到由两个过程组成的故障安全系统的严格调节：1）通过甾醇生物合成的负调节剂（HIGR STEROL ESTER 1，HISE1）抑制过量的甾醇产生，和2) 在拟南芥中通过磷脂甾醇酰基转移酶 1 (PSAT1) 将过量的甾醇转化为甾醇酯。hise1-3 psat1-2 双突变体叶片中的甾醇含量比野生型高 1.5 倍；这上调了应激反应基因的表达，导致叶片细胞活动的破坏。然而，过量甾醇对种子的影响在很大程度上是未知的。在这里，我们表明过量的甾醇会导致种子中的多种缺陷。hise1-3 psat1-2 植物的种子比野生型种子具有更高的甾醇含量，并且由于原花青素的积累而显示出比野生型种子更深的颜色。hise1-3 psat1-2 突变体的种皮异常起皱。种皮形成伴随着细胞死亡介导的内珠被收缩。在 hise1-3 psat1-2 突变体中，透射电子显微镜显示珠被的收缩受损，导致种皮较厚和种子发芽延迟。此外，psat1-2 和 hise1-3 psat1-2 种子表现出吸水缺陷。总之，结果表明过量的甾醇会损害适当的种皮形成，从而抑制种子发芽。种皮形成伴随着细胞死亡介导的内珠被收缩。在 hise1-3 psat1-2 突变体中，透射电子显微镜显示珠被的收缩受损，导致种皮较厚和种子发芽延迟。此外，psat1-2 和 hise1-3 psat1-2 种子表现出吸水缺陷。总之，结果表明过量的甾醇会损害适当的种皮形成，从而抑制种子发芽。种皮形成伴随着细胞死亡介导的内珠被收缩。在 hise1-3 psat1-2 突变体中，透射电子显微镜显示珠被的收缩受损，导致种皮较厚和种子发芽延迟。此外，psat1-2 和 hise1-3 psat1-2 种子表现出吸水缺陷。总之，结果表明过量的甾醇会损害适当的种皮形成，从而抑制种子发芽。