Transcriptome analysis reveals coordinated spatiotemporal regulation of hemoglobin and nitrate reductase in response to nitrate in maize roots

Summary 1- Considering nitrogen importance for plant growth and the environmental costs of intense fertilization, understanding the molecular mechanisms underlying the root adaptation to nitrogen fluctuations is a primary goal to develop biotechnological tools for sustainable agriculture. This research was aimed at identifying molecular factors involved in the response of maize roots to nitrate. 2- cDNA-AFLP was exploited for comprehensive transcript profiling of maize seedlings roots grown with variable nitrate availabilities. 336 different primers combinations were tested and 661 differentially regulated transcripts were identified. The expression of selected genes was studied in depth through quantitative real time PCR and in situ hybridization. 3- Over 50% of the genes identified responded to prolonged nitrate starvation and a few genes were identified putatively involved in the early nitrate signalling mechanisms. Real Time results and in situ localization analyses evidenced co-regulated transcriptional patterns in root epidermal cells for genes putatively involved in NO synthesis/scavenging. 4- Our findings, beside strengthening already known mechanisms, revealed the existence of a new complex signalling framework in which brassinosteroids (BRI1), the module MKK2-MPK6 and the fine regulation of nitric oxide homeostasis via co-expression of synthetic (NR) and scavenging (HB) components may play key functions in maize responses to nitrate.