Plant Direct

Many plant physiological processes have diurnal patterns regulated by diurnal environmental changes and circadian rhythms, but the transcriptional underpinnings of many of these cycles have not been studied in major crop species under field conditions. Here, we monitored the transcriptome of field‐grown soybean (Glycine max) during daylight hours in the middle of the growing season with RNA‐seq. The analysis revealed 21% of soybean genes were differentially expressed over the course of the day. Expression of some circadian‐related genes in field‐grown soybean differed from previously reported expression patterns measured in controlled environments. Many genes in functional groups contributing to and/or depending on photosynthesis showed differential expression, with patterns particularly evident in the chlorophyll synthesis pathway. Gene regulatory network inference also revealed seven diurnally sensitive gene nodes involved with circadian rhythm, transcription regulation, cellular processes, and water transport. This study provides a diurnal overview of the transcriptome for an economically important field‐grown crop and a basis for identifying pathways that could eventually be tailored to optimize diurnal regulation of carbon gain.