| ‘Zhongai 1’ is the first Chinese pear of ‘Jinxiang’ rootstock cultivar. It can cause dwarfing and compacting, and ‘Zhongai 1’ also had a good affinity with scion and rootstock when used as inter-rootstock, which can result in the efficient dwarf of pear varieties。Dwarfing rootstocks, such as that of the Chinese pear variety ‘Zhongai 1’, are an important resource in modern fruit production.An RNA-Seq analysis of ‘Zhongai 1’ and its progenitor non-dwarfing variety ‘Jinxiang’ revealed a set of genes which were differentially transcribed in the two varieties. In all, 46,619 putative unigenes were recovered from about 2.5 Gb of cDNA sequence acquired from each variety. About 23.25% of the unigenes were above 1,000 bp in length. Matches to an existing gene model were identified for >71% of the unigenes.Using IDE6 software analyze gene expression situration, control FDR value less than 0.05, and the highest expression of gene amount to 1.5 times the amount of minimum expression, the gene be regard as differential expression genes. Among the differentially transcribed gene set were some potential candidates for the dwarfing trait: one encoded a gibberellin 3-beta-dioxygenase, four encoded auxin-associated proteins, one encoded an LRR receptor-like serine/threonine-protein kinase, four encoded cytochrome P450 s, two encoded enzymes involved in abscisic acid synthesis, three were ethylene-responsive transcription factors, six were moisture status related proteins, two were NAC and four WRKY transcription factors. The assessment of transcript abundance derived by the RNA-Seq analysis was validated using quantitative real time PCR for ten of the differentially transcribed genes.‘Zhongai 1’ is a dwarfing rootstock selected from the open pollinated seedlings of ‘JinXiang’ pear. Previous transcriptome sequencing analysis result showed that the expression level of auxin hydrogen symporter（AHS） gene in tender leaves of ‘Zhongai 1’ was lower than that in its female parent ‘Jinxiang’. This may be one of the factors causing ‘Zhongai 1’ dwarf. In this study,we designed specific primers based on the sequence from transcriptome sequencing,and got a 1239 bp sequence from the new shoot phloem of ‘Zhongai 1’ and ‘Jinxiang’,respectively. There are no differentiate of the sequences between the two varieties,they all encode a sequence of 412 amino acids which has a sequence identity from 67% to 99% with the AHS gene in Malus domestica（NM001293843.1）, Prunus mume（XP008242099. 1）, populous trichocarpa（XP002306421.2） and Fragaria vesca（XP004287713.1）, so named it as PcAHS. qRT-PCR analysis showed that PcAHS gene expressed lower in new shoot phloem of ‘Zhongai 1’ than that in its female parent ‘Jinxiang’ during the shoot growing stage,so we speculated that there may be difference in their promoter sequences. The promoter sequences of PcAHS gene were isolated from ‘Zhongai 1’ and ‘JinXiang’ with a length of 828 bp and 888 bp respectively and a sequence identity of 89.1%. Sequence analysis showed that there is an absence fragment of 58 bp（-496 bp -553 bp） on the PcAHS gene promoter sequence of ‘Zhongai 1’. The two promoter sequences were analyzed by PLACE and PLANTCARE online,the results showed that the PcAHS gene promoter sequence of ‘Zhongai 1’ doesn`t only contain some common elements such as TATA-box and CAAT-box as same as ‘Jinxiang’, it also contains a peculiar BPBF transcription factor binding element P-box which is absent in ‘Jinxiang’. So we predicted that the missing sequence fragment and P-box element on the PcAHS gene promoter of ‘Zhongai 1’ may be the reasons causing its low expressed and affect its growth and development further by controlling the transfer of auxin. |
