Identification of Aquaporin Gene Family in Response to Natural Cold Stress in Ligustrum x vicaryi Rehd.

Plants are susceptible to a variety of abiotic stresses during the growing period, among which low temperature is one of the more frequent stress factors. Maintaining water balance under cold stress is a difficult and critical challenge for plants. Studies have shown that aquaporins located on the cytomembrane play an important role in controlling water homeostasis under cold stress, and are involved in the tolerance mechanism of plant cells to cold stress. In addition, the aquaporin gene family is closely related to the cold resistance of plants. As a major greening tree species in urban landscaping, Ligustrumx vicaryi Rehd. is more likely to be harmed by low temperature after a harsh winter and a spring with fluctuating temperatures. Screening the target aquaporin genes of Ligustrum x vicaryi responding to cold resistance under natural cold stress will provide a scientific theoretical basis for cold resistance breeding of Ligustrum x vicaryi. In this study, the genome-wide identification of the aquaporin gene family was performed at four different overwintering periods in September, November, January and April, and finally, 58 candidate Ligustrum x vicaryi aquaporin (LvAQP) genes were identified. The phylogenetic analysis revealed four subfamilies of the LvAQP gene family: 32 PIPs, 11 TIPs, 11 NIPs and 4 SIPs. The number of genes in PIPs subfamily was more than that in other plants. Through the analysis of aquaporin genes related to cold stress in other plants and LvAQP gene expression patterns identified 20 LvAQP genes in response to cold stress, and most of them belonged to the PIPs subfamily. The significantly upregulated LvAQP gene was Cluster-9981.114831, and the significantly downregulated LvAQP genes were Cluster-9981.112839, Cluster-9981.107281, and Cluster-9981.112777. These genes might play a key role in responding to cold tolerance in the natural low-temperature growth stage of Ligustrum x vicaryi.