Heat shock protein 70 is associated with duration of cell proliferation in early pod development of soybean.

Pod is an important organ for seed production in soybean. Pod size varies among soybean cultivars, but the mechanism is largely unknown. Here we reveal one of the factors for pod size regulation. We investigate pod size differences between two cultivars. The longer pod of 'Tachinagaha' is due to more cell number than in the short pod of 'Iyodaizu'. POD SIZE OF SOYBEAN 8 (GmPSS8), a member of the heat shock protein 70 (HSP70) family, is identified as a candidate gene for determining pod length in a major QTL for pod length. Expression of GmPSS8 in pods is higher in 'Tachinagaha' than 'Iyodaizu' and is highest in early pod development. The difference in expression is the result of an in/del polymorphism　which includes an enhancer motif. Treatment with an HSP70 inhibitor reduces pod length and cell number in the pod. Additionally, shorter pods in Arabidopsis hsp70-1/-4 double mutant are rescued by overexpression of GmPSS8. Our results identify GmPSS8 as a target gene for pod length, which regulates cell number during early pod development through regulation of transcription in soybean. Our findings provide the mechanisms of pod development and suggest possible strategies enhancing yield potential in soybean.

Nitrogen redistribution and its relationship with the expression of GmATG8c during seed filling in soybean.

It is well known that some nitrogen in the vegetative organs is redistributed to the seeds during seed filling in soybean (Glycine max [L.] Merrill). This redistribution is considered to affect the seed yield of soybean. However, it is still not clear when the nitrogen moves from the vegetative part to the seeds, and the relationship between nitrogen redistribution and leaf senescence has not been clarified. The soybean variety Fukuyutaka was grown in the experimental field of Saga University, Japan from 22 July to 31 October, 2014. After the first flower stage (R1), the plant samples were collected weekly and were separated into leaf, petiole, stem, podshell and seed. The nitrogen concentrations in each plant part were determined. Fresh leaf samples were provided for the determination of soluble protein and autophagy gene GmATG8c expression. The nitrogen that accumulated in the vegetative parts reached its highest level at 60days after sowing (DAS), then began to decrease at 73DAS (R6). This decrease is considered to be the consequence of nitrogen redistribution from the vegetative parts to the seeds. The movement of nitrogen from the vegetative parts to the seeds was estimated to occur at around 73DAS (R6). At this stage, leaf SPAD values, leaf nitrogen, and soluble protein concentrations began to decrease simultaneously, suggesting the onset of leaf senescence. Furthermore, the expression of the autophagy gene GmATG8c in the leaves increased dramatically from 73 to 85DAS, which is the duration of nitrogen redistribution. The results suggest that the nitrogen redistribution from the vegetative parts to the seeds could be one of the initiating factors of leaf senescence, and the autophagy gene GmATG8c was associated with this process.