Objective Expressions of ZmPHYB2 in the maize inbred lines from temperate and tropical regions exposed to varied photoperiods were determined to understand the phytochromic mechanism of the plants.

Method The different maize inbred lines, CML288 from a tropical region and Huangzaosi from a temperate zone, were placed under night-break (NB) after a short 9h photoperiod day (SD) for an extended period. Flowering of the plants were monitored. ZmPHYB2 were cloned using the homologous cloning method for a bioinformatic analysis, and expressions of the genes in 48h under the treatment determined by qRT-PCR.

Result NB significantly delayed flowering of the tropical CML288, but accelerated that of Huangzaosi. There were 19 single-nucleotide polymorphisms in the coding sequences (CDS) of ZmPHYB2 of the two lines, and 7 differentiated amino acids including 5 localized in two conserved domains. The changed photo-exposure significantly disrupted the ZmPHYB2 expression in the CML288 leaves and lowered the transcript level in the leaves of Huangzaosi.

Conclusion It appeared that the 5 different amino acids in two conserved domains of ZmPHYB2, the perturbed ZmPHYB2 expression in CML288 leaves, and the downregulated ZmPHYB2 expression in Huangzaosi leaves introduced by NB contributed to the delayed flowering in the tropical CML288 in comparison to the temperate counterparts.