Abstract:

Exogenous ethylene has been widely used to induce pineapple flowering，but the molecular mechanism behind ethephon induction is still unclear. Three genes encoding auxin efflux carriers （designated as AcPIN1，AcPIN2 and AcPIN3），and two genes encoding auxin influx carriers（designated  as AcAUX1 and AcAUX2）were isolated from the pineapple（Ananas comosus L.‘Perola’）shoot apex using RT-PCR and RACE. The full-length cDNA of AcPIN1，AcPIN2，AcPIN3，AcAUX1 and AcAUX2 were 2 690，2 388，2 057，2 156 and 1 580 bp，with the open reading frames of 1 854，1 917，1 530，1 479 and 1 392 bp，which encode a putative protein of 617，638，509，492 and 463 amino acids，respectively. The genomic DNA sequences of AcPIN1，AcPIN2，AcPIN3，AcAUX1 and AcAUX2 were 3 602，3 208，4 204，5 457 and 2 436 bp，with the lengths of 3 244，2 780，3 947，5 264 and 2 321 bp，respectively，from the start codon to the terminator codon. The results of a phylogenetic tree analysis indicated that AcPINs and the AcAUXs belong to plant PINs and AUXs/LAXs groups. Quantitative real-time PCR indicated that the relative expressions of AcPINs were up-regulated much more than AcAUXs after the treatment of 200 and 1 200 mg · L^-1 ethephon. The expression of AcPIN2 was significantly increased at the former period（1–2 d）and the later period（28–37 d）after the treatment. In contrast，the expressions of AcPIN1 and AcPIN3 were significantly up-regulated at most time points after the treatment. On the other hand，the up-regulated expression of AcAUX1 was mainly on the former period（1 d）and later period（28–37 d），while the significantly up-regulated expression of AcAUX2 was only found at the former period（1，2 and 9 d after the treatment）. The results showed that there were polar auxin transport during the flowering of pineapple，and auxin efflux might play a more important role during this process.

Key words: Ananas comosus, flowering, auxin efflux carrier, auxin influx carrier, polar auxin transport