No abstract

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.

No abstract

Pod size of soybean is an important factor in the determination of seed weight. However, little is known about pod growth of soybean. Brassinosteroid, a group of phytohormones, regulate the pod growth of faba bean. We therefore investigated the role of brassinosteroid in pod growth of soybean. We measured pod length and cell number and cell area in pods treated with a brassinosteroid biosynthesis inhibitor. The inhibitor suppressed pod growth through the reduction of cell area. We then examined pod morphology and the expression of brassinosteroid biosynthesis (GmCYP450 85A1, 2 and 3) and response (GmBZR1, GmBES1 and GmBRU1) genes in the pods of two cultivars that differ in pod size. The difference in pod size was attributable to cell area, and the expression of brassinosteroid biosynthesis and response genes in pods was higher in the cultivar that has large pods. These results suggest that pod size of soybean is regulated through cell hypertrophy caused by brassinosteroid.

Pod setting rate in soybean is an important trait that determines pod number, which is highly correlated with seed yield. Using two soybean cultivars with different pod setting rates, we examined the relationship between plant growth regulation by gibberellin (GA) and pod setting rate. Plant growth rate (PGR) after flowering was significantly higher in 'Fukuyutaka' (low pod setting rate) than in 'Kariyutaka' (high pod setting rate); this difference was caused by increasing of GA biosynthesis-related genes expression. Additionally, pod setting rate in 'Fukuyutaka' was lower than that in 'Kariyutaka'. Furthermore, when 'Kariyutaka' was treated with GA after flowering, the PGR increased and pod setting rate decreased. These results suggest that pod setting rate in soybean is regulated by vegetative growth after flowering through GA biosynthesis.