Abstract

To increase the genetic diversity of maize grown in temperate zones, it is essential that tropical germplasm be integrated, but a major limiting factor is photoperiod sensitivity. To address the molecular basis of this sensitivity, a tropical maize inbred line CML288 was grown under inductive short-day (SD) and non-inductive night break (NB) conditions in which the inductive dark period was broken by a brief illumination. Homologous amplification and rapid amplification of cDNA ends (RACE) technology were used to clone the maize HD6gene, an ortholog of rice Hd6 that is involved in the photoperiodic flowering pathway, and functions as a critical component of the circadian clock. Detailed expression analysis of this gene were conducted using real-time fluorescence quantitative PCR in the stem apexes and leaves at the 5th-leaf stage, the developmental stage most sensitive to NB. The results demonstrated that diurnal expression rhythms of HD6 were altered in both the stem apexes and the leaf by NB treatment, and its mRNA accumulation gradually declined with the increase of NB treatment days. Additionally, the degree of delay in day to tassel (DTT) and day to pollen (DTP) was also proportional to the number of NB treatment days. The consistent effect of NB on HD6 accumulation, together with the flowering delay suggests that the HD6 gene may participate in the photoperiodic floral induction.

Key words: Maize (Zea mays L.), night break, HD6 gene, expression analysis, photoperiod sensitivity.