Background: Nitrate uptake is a highly regulated process. Understanding the intricate interactions between nitrate
availability and genetically-controlled nitrate acquisition and metabolism is essential for improving nitrogen use
efciency and increasing nitrate uptake capacity for plants grown in both nitrate-poor and nitrate-enriched environ‑
ments. In this report, we introduced into tobacco (Nicotiana tabacum) the constitutively expressed maize high-afnity
transporter ZmNrt2.1 gene that would bypass the tight control for the endogenous nitrate-responsive genes. By
using calcium inhibitors and varying levels of NO3
−, Ca2+ and K+, we probed how the host plants were afected in
their nitrate response.... More
Background: Nitrate uptake is a highly regulated process. Understanding the intricate interactions between nitrate
availability and genetically-controlled nitrate acquisition and metabolism is essential for improving nitrogen use
efciency and increasing nitrate uptake capacity for plants grown in both nitrate-poor and nitrate-enriched environ‑
ments. In this report, we introduced into tobacco (Nicotiana tabacum) the constitutively expressed maize high-afnity
transporter ZmNrt2.1 gene that would bypass the tight control for the endogenous nitrate-responsive genes. By
using calcium inhibitors and varying levels of NO3
−, Ca2+ and K+, we probed how the host plants were afected in
their nitrate response.
Results: We found that the ZmNrt2.1-expressing plants had better root growth than the wild type plants when Ca2+
was defcient regardless of the nitrate levels. The growth restriction associated with Ca2+-defciency can be alleviated
with a high level of K+. Furthermore, the transgenic plants exhibited altered expression patterns of several endog‑
enous, nitrate-responsive genes, including the high- and low-afnity nitrate transporters, the Bric-a-Brac/Tramtrack/
Broad protein BT2 and the transcription factor TGA-binding protein TGA1, in responding to treatments of NO3
−, K+
or inhibitors for the calcium channel and the cytosolic Ca2+-regulating phospholipase C, as compared to the wild
type plants under the same treatments. Their expression was not only responsive to nitrate, but also afected by Ca2+.
There were also diferent patterns of gene expression between roots and shoots.
Conclusion: Our results demonstrate the ectopic efect of the maize nitrate transporter on the host plant’s overall
gene expression of nitrate sensing system, and further highlight the involvement of calcium in nitrate sensing in
tobacco plants.
