Microarray analysis reveals early responsive genes possibly involved in localized nitrate stimulation of lateral root development in maize (Zea mays L.)

Arable soils are extremely heterogeneous in spatial nutrient distribution. It is well documented that lateral roots (LRs) proliferate in nitrate-rich patch. Yet less information is available as to which genes are involved in this process, in particular in cereals. To understand the molecular mechanism for local nitrate-induced LR growth in maize (Zea mays L.), we analyzed the gene expression profiling in maize root in early response (1 h) to local nitrate stimulation by using Maize Oligonucleotide Array (http:// www.maizearray.org) and a split-root system. Selected differentially expressed genes were further confirmed by semi-quantitative RT-PCR. The results showed that reception and/or transduction of local NO3- signal involve some important protein kinases and protein phosphatases (histidine kinases. serine/ threonine kinases, protein phosphatase 2A, etc.) and transcription factors (F-box, Zinc finger, Myb and bZIP transcription factors and response regulator). Increasing expression of genes encoding auxin response factor 7b, ethylene receptor, and cytokinin oxidase suggests strong interaction among hormonal pathways and local NO3- signaling pathways. Genes involving NO3- uptake and assimilation (NRT2.1, NR, etc.), sugar transport (a sugar transporter) and utilization (a sucrose synthase) were enhanced in the N-fed root. Furthermore, local NO3- induces rapid expression of genes related to cell division and expansion such as a-expansin, cellulose synthase, kinesin, plasma membrane and tonoplast aquaporins. Based on the differentially expressed genes, a putative model which combines both the "NO3- signal" and "metabolic sink" theories is proposed to explain the molecular mechanism controlling local nitrate-induced LR elongation in maize. (c) 2008 Elsevier Ireland Ltd. All rights reserved.