Expression response of Rubisco and GS isoform gene to the ratio of tillering and heading nitrogen fertilization at rice filling stage

Objectives Nitrogen nutrition affects the transcription level of ribulose 1, 5-bisphosphate carboxylase/oxygenase (Rubisco) and glutamine synthetase (GS) gene, and studying the relationship between the gene expression and nitrogen supply levels will help understanding mechanism of nitrogen nutrition on rice growth and nitrogen use efficiency at the molecular regulation level.

Methods In a pot experiment, two rice cultivars of multi-panicle and high yield type and heavy panicle and super japonica cultivar in cold region were used as test materials. The N∶P₂O₅∶K₂O input ratio was 1∶0.5∶1. Half of N fertilizer was basal applied, the left was divided into tillering fertilizer and panicle fertilizer, and four ratios of tillering to panicle fertilizers were designed, 10%∶40%, 20%∶30%, 30%∶20% and 40%∶10%. The transcription expression of Rubisco and GS gene and the accumulation of different forms of nitrogen in rice leaves at the filling stage were investigated.

Results The results showed that the contents of total N, NO₃^–-N and NH₄⁺-N of leaves and grains of rice were significantly increased with the increase of the tillering fertilizer rate. Simultaneously, the expression levels of the large and small subunit genes of Rubisco were increased in different extents, among them the expression levels ofOsRBCSL,OsRBCS2 andOsRBCS4 were up-regulated significantly, while those ofOsRBCS3 andOsRBCS5 were up-regulated to some extent, and the high expression duration of Rubisco subunits gene were extended. The expression levelofOsGS1;1 in leaves and grains was enhanced at the middle and late filling stage, while those ofOsGS2 gene only showed high expression level in leaves at the middle and late filling stage, and those ofOsGS1;3 gene exhibited high expression level during the whole filling stage. The expression levels of five rubisco subunit genes had significant or highly significant positive correlation with the contents of NO₃^–-N and total nitrogen in leaves, and the expression levels of three glutamine synthetase isoenzyme gene had significant or highly significant positive correlation with the contents of NH₄⁺-N and total nitrogen in leaves and grains.

Conclusions The expression dynamic ofOsRBCL and GS genes are not responded to different cultivars or nitrogen supply during the filling stage. High contents of NO₃^–-N and total nitrogen in leaves significantly increased the amount of Rubisco gene transcriptional expression, and high contents of NH₄⁺-N and total nitrogen in leaves and grains significantly increased the amount of GS gene transcriptional expression.