Genome-wide identification of OSCA gene family members and their expression under different abiotic stresses in kiwifruit

Abstract:【Objective】Hyperosmotic gated non-selective calcium-permeable cation channels (OSCA) play a key role in sensing exogenous and endogenous osmotic changes and regulating plant growth and development. The aim of this study was to identify key candidate OSCA genes involved in responses to different abiotic stresses by analyzing their expressions in kiwifruit.【Methods】Bioinformatics methods were used to identify OSCA family genes in the genome of Actinidia chinensis‘Red 5’, and to analyze their sequence property, phylogenetic relationship, chromosomal localization, gene structure, cisacting elements and synteny relationship. Tissue- cultured plantlets of Actinidia deliciosa‘Hayward’ was used as the plant material. A total of four stress treatments were carried out in the experiment: drought stress (15% PEG6000 solution), salt stress (150 mmol L- 1 NaCl solution), high temperature stress (42 ℃), and low temperature stress (4 ℃). The leaves were sampled at 0 h (control), 24 h and 48 h, respectively. The relative expressions of those OSCA genes under different abiotic stress conditions were analyzed by using the quantitative real-time PCR method.【Results】In this study, 16 OSCA genes were identified in the genome of kiwifruit, they were named AcOSCA1-AcOSCA16 according to their chromosomal localization, and they were distributed on 13 chromosomes. In order to clarify the evolutionary and kinship relationships between members of the OSCA protein family and their homologousproteins in other plants, OSCA protein sequences of rice, Arabidopsis, tomato and kiwifruit were used to construct a phylogenetic tree. Phylogenetic analysis revealed that they could be categorized into four groups, and the syntenic analysis results showed that there were 24 gene pairs with syntenic relationships between 15 AcOSCA genes in kiwifruit and 13 AtOSCA genes in Arabidopsis. Cis-acting element analysis showed that there were many cis-acting elements in the promoter regions of related AcOSCA genes that responded to hormones, adversity stress, and defense and stress responses. Those cis-acting elements included six stress- associated elements, i.e., drought- inducible MYB- binding site (MBS), CAAT-box, anaerobically-induced-associated cis-acting regulator (ARE), defense and stress response elements (TC- rich), low-temperature-induced cis- acting element (LTR), and anaerobically-induced enhancer-like cis-acting element (GC-motif); and four hormone-associated cis-acting elements: abscisic acid-responsive cis-acting element (ABRE), gibberellin-responsive element (GARE-motif), methyl jasmonate- responsive element (TGACG motif/CGTCA- motif), and gibberellin- responsive element (Pbox). It was found that most of those AcOSCA genes were responsive to drought, salt, low and high temperature stresses, and different AcOSCA members exhibited various expression patterns under these abiotic stresses. Specifically, under drought stress induced by 15% PEG6000, the expressions of most kiwifruit OSCA genes were up-regulated after they were subjected to drought stress, except for OSCA2 and OSCA9, both of which showed down expressions at 24 h after treatment when compared with the control (0 h). Among those OSCA genes, when compared with the control, OSCA3, OSCA7, OSCA8 and OSCA15 were up-regulated to 3.0, 3.2, 3.8 and 3.1-fold at 24 h, respectively. At 48 h after treatment, the relative expression levels of OSCA8 was the highest, with a value of 2.5- fold higher than the control. Under salt stress induced by 150 mmol L-1 NaCl solution, most OSCA genes, except OSCA1, showed upregulated expressions at 24 h and 48 h when compared with the control. Among them, the expressions of OSCA3, OSCA8 and OSCA12 increased to 3.2, 5.3 and 2.8 times higher than that of the control (0 h) at 24 h, respectively, and at 48 h, were up-regulated to 3.4, 10.0 and 4.0 times of the control (0 h), respectively. Under high temperature stress condition (42 ℃), expression of OSCA3 was up-regulated at 24 h, with a value of 2.9 times higher when compared with the control at 0 h, however, at 48 h after treatment, its expression level was lower than the control. Under low temperature stress (4 ℃), OSCA3 and OSCA14 were both up-regulated at 24 h, with values of 2.9- and 2.4-fold higher than the control (0 h), respectively. Compared with the control at 0 h, the relative expression level of OSCA8 increased to 2.1 (24 h) and 2.9 times (48 h), respectively. And the highest expression level was found for OSCA1 at 48 h, with a value of 3.4-fold higher than the control. These results showed that expression of OSCA3 was greatly up- regulated under drought, salt, high temperature and low temperature stresses. OSCA8 was significantly induced by drought, salt and low temperature stresses. OSCA1 and OSCA14 were upregulated under low-temperature stress conditions. OSCA7 and OSCA15 were induced by drought stress treatment. Therefore, these 6 OSCA genes were closely related to relative abiotic stresses and they may play important roles in responses to the abiotic stresses of drought, salt, high or low temperature.【Conclusion】The family members of OSCA genes were identified in the genome of kiwifruit. Information of kiwifruit OSCA gene family members was analyzed, and their functions were predicted. Six OSCA genes were identified to be key candidate genes in the responses to the stresses of drought, salt, high temperature or low temperature. This study provided a basis for further research on the molecular functions of related OSCA genes in response to abiotic stresses in kiwifruit.