Abstract:

Members of the DMP genefamily are plant-specific membrane proteins that play an important role in plant reproductive development and senescence. Flax （Linum usitatissimum） is an important oil and cash crop in China. However， there are no reports on the distribution and functions of the DMP gene family in this flax species. We identified the members of the DMP gene family in flax using bioinformatics analyses， and determined their sequence characteristics， phylogeny， and duplication events. Transcriptome data and quantitative reverse-transcription polymerase chain reaction （qRT-PCR） analyses were used to analyze the transcriptional profiles of LuDMP genes in different tissues and organs and under stress treatments. Seventeen LuDMP genes， designated as LuDMP-1 to LuDMP-17， were identified from the Longya-10 cultivar by homology analysis， and were found to be unevenly distributed on nine chromosomes. Sequence characteristics analysis showed that only LuDMP-9， LuDMP-16， and LuDMP-17 had an intron and the other members had none. All members of the LuDMP family contained many cis-acting elements related to hormone and stress responses in their promoter regions. The coding sequences encoded polypeptides with lengths ranging from 195 to 240 amino acids， molecular weights ranging from 20946 to 25830 Da， and theoretical isoelectric points ranging from 4.76 to 9.71. All LuDMP proteins were predicted to be hydrophobic with two to five transmembrane domains and four to eight motifs. Four motifs were present in all LuDMP proteins. Most LuDMP proteins were predicted to localize in the cell membrane. Three tandem duplication and eight segmental duplication gene pairs were identified in the LuDMP gene family， which has been under strong purification selection during the evolution of flax. Transcriptome analyses showed that most LuDMP members are specifically expressed in the fruit and stem. In a phylogenetic analysis， the 17 DMP proteins were divided into five subgroups. Subgroup III was the largest， with 11 members. The DMP proteins in each subfamily exhibited monocotyledon-specific or dicotyledon-specific clustering patterns. LuDMP-1 and LuDMP-7 in subgroup IV showed the highest homology with haploid induction genes in Arabidopsis and maize （Zea mays） and were located in the same evolutionary branch， with sequence homology higher than 67%. Moreover， these two genes showed the highest transcript levels in the mature anther， suggesting that they are candidate genes for inducing flax haploids. We cloned LuDMP-1 from Longya-10 （full-length coding sequence， 699 bp）. The promoter regions of LuDMP-1/7 contained hormone- and stress-responsive elements， and both genes showed increased transcript levels under auxin （indole acetic acid， naphthalene acetic acid）， gibberellin， polyethylene glycol， and high temperature and low temperature treatments. Their responses to low temperature and high temperature were the most obvious， with transcript levels increased to 260 times and 600 times that in the control， respectively. The results of this study lay a foundation for elucidating the functions of LuDMPs and identify genetic resources for haploid breeding of flax.

Key words: flax, DMP gene family, haploid induction, expression analysis