Transcripts and low nitrogen tolerance: Regulatory and metabolic pathways in sugarcane under low nitrogen stress

Abstract

Understanding the molecular regulatory mechanism of physiological characteristics is essential to improve low nitrogen (N) tolerance in sugarcane. We selected sugarcane varieties ROC22 (low N-tolerant variety) and Badila (low N-sensitive variety) as experimental materials, and N sensitivity indexes (NSIs) of plant fresh weight and plant N accumulation in ROC22 was respectively 38.18% and 17.44% lower than that of Badila. Based on the morphological and physiological measurements and the expression of eight key genes in N metabolism, the leaves (6 h) and roots (3 h) of ROC22 and Badila under low N condition (0.6 mM N) were selected for RNA-Seq analysis. In the leaves and roots, the total and up-regulated numbers of differentially expressed genes (DEGs) in ROC22 was significantly higher than that of Badila. The specific DEGs in the ROC22 leaves mainly enriched in photosynthesis and N metabolism, whereas those in the ROC22 roots mainly enriched in N metabolism and the hormone signal transduction pathway. MYB was the largest differentially expressed transcription factor (TF) gene family in both varieties, followed by AP2-EREBP. In the leaves and roots of ROC22, several genes related to IAA and ABA hormone pathways, N assimilation process, and PSI and PSII of the photosynthesis pathways modulated the physiological characteristics under low N stress, correspondingly, IAA concentration increased by 11.47% (leaves) and 9.24% (roots), and glutamine synthetase (GS) enzyme activities increased by 28.13% (leaves) and 36.97% (roots), which may explain the observed differences in low N tolerance between ROC22 and Badila. This study has provided a basis for improvement of sugarcane in adapting to low N conditions.