Phosphate starvation of maize inhibits lateral root formation and alters gene expression in the lateral root primordium zone

Background: Phosphorus (P) is an essential macronutrient for all living organisms. Maize (Zea mays) is an important human food, animal feed and energy crop throughout the world, and enormous quantities of phosphate fertilizer are required for maize cultivation. Thus, it is important to improve the efficiency of the use of phosphate fertilizer for maize. Results: In this study, we analyzed the maize root response to phosphate starvation and performed a transcriptomic analysis of the 1.0-1.5 cm lateral root primordium zone. In the growth of plants, the root-to-shoot ratio (R/L) was reduced in both low-phosphate (LP) and sufficient-phosphate (SP) solutions, but the ratio (R/L) exhibited by the plants in the LP solution was higher than that of the SP plants. The growth of primary roots was slightly promoted after 6 days of phosphate starvation, whereas the numbers of lateral roots and lateral root primordia were significantly reduced, and these differences were increased when associated with the stress caused by phosphate starvation. Among the results of a transcriptomic analysis of the maize lateral root primordium zone, there were two highlights: 1) auxin signaling participated in the response and the modification of root morphology under low-phosphate conditions, which may occur via local concentration changes due to the biosynthesis and transport of auxin, and LOB domain proteins may be an intermediary between auxin signaling and root morphology; and 2) the observed retardation of lateral root development was the result of co-regulation of DNA replication, transcription, protein synthesis and degradation and cell growth. Conclusions: These results indicated that maize roots show a different growth pattern than Arabidopsis under low-phosphate conditions, as the latter species has been observed to halt primary root growth when the root tip comes into contact with low-phosphate media. Moreover, our findings enrich our understanding of plant responses to phosphate deficits and of root morphogenesis in maize.