Abstract
Brassinosteroids (BRs) are steroid hormones that function in plant growth and development and response to environmental stresses and nutrient supplies. However, few studies have investigated the effect of BRs in modulating the physiological response to nitrogen (N) supply in maize. In the present study, BR signaling-deficient mutant zmbri1-RNAi lines and exogenous application of 2,4-epibrassinolide (eBL) were used to study the role of BRs in the regulation of physiological response in maize seedlings supplied with N. Exogenous application of eBL increased primary root length and plant biomass, but zmbri1 plants showed shorter primary roots and less plant biomass than wild-type plants under low N (LN) and normal N (NN) conditions. LN induced the expression of the BR signaling-associated genes ZmDWF4, ZmCPD, ZmDET2, and ZmBZR1 and the production of longer primary roots than NN. Knockdown of ZmBRI1 weakened the biological effects of LN-induced primary root elongation. eBL treatment increased N accumulation in shoots and roots of maize seedlings exposed to LN or NN treatment. Correspondingly, zmbri1 plants showed lower N accumulation in shoots and roots than wild-type plants. Along with reduced N accumulation, zmbri1 plants showed lower NO3− fluxes and 15NO3− uptake. The expression of nitrate transporter (NRT) genes (ZmNPF6.4, ZmNPF6.6, ZmNRT2.1, ZmNRT2.2) was lower in zmbri1 than in wild-type roots, but eBL treatments up-regulated the transcript expression of NRT genes. Thus, BRs modulated N physiological response and regulated the transcript expression of NRT genes to promote N uptake in maize.
