High temperatures during seed development can affect the seed yield and quality in many crops. Here, we analyzed how high temperature alters the main seed storage compounds (lipid and protein) in soybean. At five days after R5 stage (initial seed filling stage), soybean plants were treated with control (20/20ºC day/night) and high temperature (30/30ºC day/night). After treatment, immature seed was sampled, analyzed for lipid and protein contents and for expression of seed storage compounds related genes. High temperature during seed filling increased lipid content but decreased protein content, associating with yield reduction. It increased the expression of two genes related to seed lipid biosynthesis (GmBCCP2 and GmKAS1) and genes for a lipid biosynthesis regulator (GmWRI1) and its transcription factor (GmDREBL), and decreased the expression of genes related to lipid degradation such as GmACXs. High temperature downregulated genes related to seed storage protein (GmGy1, GmGy2, GmGy4, GmGy5 and Gmβ-conglycinin) and upregulated genes for cysteine and aspartate proteinases. Therefore, high temperature during seed filling preferentially accumulates lipid than protein content in seed, although seed yield reduction was associated with lower seed protein content in soybean. Our study provides insights for further improvements of soybean seed oil under abiotic stress such as heat stress. Abbreviations: DAT: days after treatment; TF: transcription factor; DREBL: Dehydration-responsive Element-binding L; WRI1: Wrinkled 1; PK: Ketoacyl acyl carrier protein synthase 1; PEP: phosphoenolpyruvate; BCCP2: Biotin carboxyl carrier protein; KAS1: ketoacyl acyl carrier protein synthase 1; ACX: Acyl-coenzyme A peroxidase; MS: Malate synthase; PEPCK: Phosphoenolpyruvate carboxykinase; Gy: Glycinin; CysP: Cysteine Proteinase; SoyAP: Aspartic Proteinase; EF1b: Elongation factor 1b.
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