Isolation and expression analysis of CiNIP5, a citrus boron transport gene involved in tolerance to boron deficiency

It was reported that AtNIP5;1 is responsible for boron (B) uptake into the root under B-deficient conditions. In this study, we cloned an NIP5-like gene (named as CiNIP5) from Trifoliate orange. The full length of CiNIP5 was 1470 bp in which 903 bp formed the open reading frame, coding a protein of 300 amino acids. Sequence analysis showed that CiNIP5 had a highly conserved Asn-Pro-Ala (NPA) region and aromatic/arginine (ar/R) motif and it belongs to Nodulin 26-like intrinsic protein (NIP) group II. Analysis of gene expression indicated that CiNIP5 expressed mainly in the roots of citrus seedlings, and it increased obviously under B-deficiency but was suppressed under B toxicity. Additionally, the responses of CiNIP5 expression to B deficiency were compared between the roots of Carrizo citrange and Fragrant citrus, in which the former showed more tolerance than the latter to low B condition in field practice. CiNIP5 transcript level in the root of Carrizo citrange was induced and increased continuously to 7.7 times at 48 h after B deficient treatment (HABdT) as compared with that at 0 HABdT while in the root of Fragrant citrus it was induced to 4.4 times at 24 HABdT, and then decreased to half at 48 HABdT. The possible role of CiNIP5 was discussed in the mechanism of B-uptake efficiency of different rootstocks under B-deficiency.