Circadian Clock Regulation in Soybean Senescence: A Transcriptome Analysis of Early and Late Senescence Types

We obtained early-senescence (ES)- and late-senescence (LS)-type F7 plants from a cross between a hybrid (Glycine max × Glycine soja) and the Glycine max cultivar. The ES-type plants presented the reproductive (R2) growth stage at 50 days after sowing (DAS) and the R7 growth stage at 95 DAS, whereas the LS-type plants presented the beginning of the R1 and R6 growth stages at 50 and 95 DAS, respectively. To understand the molecular mechanisms underlying this senescence, we performed transcriptome analysis of leaves from 50 and 95 DAS of ES- and LS-type plants. A total of 2,414 and 2,471 genes at 50 and 95 DAS, respectively, were differentially expressed between ES-type and LS-type plants. Twenty-three candidate genes associated with the circadian clock, chlorophyll biosynthesis, phytohormones, and protein kinases were identified, and their expression levels were analyzed. In addition, we analyzed the expression patterns of circadian clock-related genes such as CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), LATE ELONGATED HYPOCOTYL (LHY), CONSTANS-LIKE 9 (COL9), EARLY FLOWERING 3 (ELF3) and pseudo response regulator 5 (PRR5) in ES- and LS-type plants under light and dark conditions. The expression patterns of circadian clock-related genes were similar in the ES- and LS-type plants. However, the transcription levels of these genes were compared between ES- and LS-type plants, and the expression of these genes was greater than that in LS-type plants during the period when expression increased. Therefore, each set of candidate genes regulated senescence in each plant by regulating their expression level. To investigare the differentially expressed genes between early and late senscence type soybean plants in 50 and 95 days