Identification of Aquaporin Gene Family in Response to Natural Cold Stress in Ligustrum × Vicaryi Rehd.

Background: Maintaining water balance in various adversities is a difficult and critical challenge for plants. Studies have shown that aquaporins located on cytomembrane play an important role in maintaining water homeostasis under various environmental stresses. Some studies have shown that aquaporins are involved in the tolerance mechanism of plant cells under cold stress, and the aquaporin gene family is closely related to the cold resistance of plants. Ligustrum × vicaryi Rehd. plays a significant role in urban landscaping with poor cold resistance at the seedling stage and early planting stage. Screening the target aquaporin genes of Ligustrum × vicaryi related to cold resistance during natural cold stress will provide a scientific theoretical basis for cold resistance breeding of Ligustrum × vicaryi.Results: 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 × vicaryi aquaporin (LvAQP) genes were identified. The phylogenetic analysis revealed that four subfamilies of the LvAQP gene family: 32 PIPs, 11 TIPs, 11 NIPs, and 4 SIPs, among which there were more genes in the PIPs subfamily than that in other plants. The key LvAQP genes were found through analyzing aquaporin genes related to cold stress in other plants and LvAQP genes expression profiles. The up-regulated key LvAQP genes were Cluster-9981.114831, Cluster-9981.104986, and Cluster-9981.120365, and the down-regulated key LvAQP genes were Cluster-9981.112839, Cluster-9981.109034, Cluster-9981.89369, Cluster-9981.110451, Cluster-9981.107281, Cluster-9981.112777, Cluster-9981.112789, Cluster-9981.122691 and Cluster-9981.88037. These genes play a key role related to cold tolerance in the nature low temperature growth stage of Ligustrum × vicaryi. Conclusions: This study systematically identified the AQP gene family in Ligustrum × vicaryi and screened for 20 differential expression LvAQP genes related to cold stress, among which 11 genes belonged to PIPs subfamily. The results of this research will lay the foundation for further biological function verification of cold resistance-related aquaporin candidate genes in Ligustrum × vicaryi, especially PIPs subfamily, and provide theoretical basis and technical support for improving seedling quality and breeding.

Overexpression of a Banana Aquaporin Gene MaPIP1;1 Enhances Tolerance to Multiple Abiotic Stresses in Transgenic Banana and Analysis of Its Interacting Transcription Factors

Aquaporins can improve the ability of plants to resist abiotic stresses, but the mechanism is still not completely clear. In this research, overexpression of MaPIP1;1 in banana improved tolerance to multiple stresses. The transgenic plants resulted in lower ion leakage and malondialdehyde content, while the proline, chlorophyll, soluble sugar, and abscisic acid (ABA) contents were higher. In addition, under high salt and recovery conditions, the content of Na+ and K+ is higher, also under recovery conditions, the ratio of K+/Na+ is higher. Finally, under stress conditions, the expression levels of ABA biosynthesis and response genes in the transgenic lines are higher than those of the wild type. In previous studies, we proved that the MaMADS3 could bind to the promoter region of MaPIP1;1, thereby regulating the expression of MaPIP1;1 and affecting the drought tolerance of banana plants. However, the mechanism of MaPIP1;1 gene response to stress under different adversity conditions might be regulated differently. In this study, we proved that some transcription factor genes, including MaERF14, MaDREB1G, MaMYB1R1, MaERF1/39, MabZIP53, and MaMYB22, showed similar expression patterns with MaPIP1;1 under salt or cold stresses, and their encoded proteins could bind to the promoter region of MaPIP1;1. Here we proposed a novel MaPIP1;1-mediated mechanism that enhanced salt and cold tolerance in bananas. The results of this study have enriched the stress-resistant regulatory network of aquaporins genes and are of great significance for the development of molecular breeding strategies for stress-resistant fruit crops.

Genome-Wide Identification of Aquaporin Gene Family in Pitaya Reveals an HuNIP6;1 Involved in Flowering Process

Aquaporins (AQPs) are essential membrane proteins involved in seed maturation and germination, stomata movement, photosynthesis, and regulation of plant flowering processes. Pitaya flowers are open at night and wither at daybreak, which shows an obvious circadian rhythm. In this study, a comprehensive genome-wide analysis of AQPs in Hylocereus undantus was conducted to screen key genes associated with flowering processes. A total of 33 HuAQP genes were identified from the H. undantus genome. The 33 HuAQPs were grouped into four subfamilies: 10 PIPs, 13 TIPs, 8 NIPs, and 2 SIPs, which were distributed on 9 out of 11 pitaya chromosomes (Chr) (except for Chr7 and Chr10). Results from expression profiles showed that HuNIP6;1 may be involved in pitaya’s floral opening. HuNIP6;1 was localized exclusively in the cell membrane. Overexpression of HuNIP6;1 in Arabidopsis thaliana significantly promoted early flowering through regulating negative flowering regulators of MJM30, COL9, and PRR5, suggesting that HuNIP6;1 plays key roles in regulating flowering time. The present study provides the first genome-wide analysis of the AQP gene family in pitaya and valuable information for utilization of HuAQPs.