Genome-wide transcriptome analysis of roots in two rice varieties in response to alternate wetting and drying irrigation

Alternate wetting and drying (AWD) irrigation has been widely used as an efficient rice production method to obtain better yield without continuous flooding (CF) of the paddy field. However, how this practice affects gene expression to regulate rice physiology and morphology is largely unknown. In this study, we used two rice varieties, Nipponbare, a lowland rice cultivar, and Gaoshan 1, an upland cultivar, and found that root dry weight (RDW) and root oxidation activity (ROA) in both cultivars substantially increased in response to AWD. We then analyzed the differences in transcriptome profiles of their roots irrigated in AWD vs. CF conditions. AWD responsive genes are mainly involved in lignin biosynthetic pathway and phytohormone signal transduction pathway and belong mainly to bHLH, bZIP, NAC, WRKY, and HSF transcription factor families. We discussed how these differentially expressed genes may contribute to the morphological adaptations observed in roots exposed to AWD. This analysis also provides useful information to explain the similarities and differences in adaptation to AWD irrigation between the two rice ecotypes.