Abstract
The pyrabactin resistance (PYR)/PYR1-like (PYL)/regulatory components of ABA receptor (RCAR) (known as PYLs for short) have been identified and characterized as the ABA receptors in some plants. However, little is known about the details regarding PYL family genes in the apple (Malus domestica). In this study, we identified 13 apple PYLs, termed MdPYL1-13, which could be classified into four groups according to structural features of the amino acid sequence. The gene structures and conserved motifs analysis found that the majority of MdPYLs had a similar number of exons and similar conserved motif profile in the same group. In addition, 11 gene pairs were identified to exhibit synteny by synteny analysis between the apple and Arabidopsis. Furthermore, we investigated MdPYLs transcript level in various organs of the red-fleshed apple (Malus sieversii f. Neidzwetzkyana (Dieck) Langenf) ‘Xinjiang No.1’. The results suggested all MdPYLs within group I were expressed at relatively higher levels in all of the organs tested. However, the genes of group IV had little or no variation. Additionally, we found various hormone and stress-related cis-elements in the promoters of MdPYLs by analyzing cis-elements. Therefore, the expression levels of all MdPYLs were further detected under ABA, PEG, salt, and cold stresses in ‘Xinjiang No.1’ seedlings. We found that all MdPYLs except for MdPYL11 were upregulated by ABA treatment, 10 genes were upregulated by PEG treatment, 12 genes were upregulated by NaCl treatment, and six genes were upregulated by cold treatment (4 °C) while seven genes were downregulated. Thus, these MdPYLs might be involved in the defense against abiotic stresses. In addition, the interaction between 13 MdPYLs and two 2C protein phosphatases in the apple (MdPP2C65 and MdPP2C72) was investigated in yeast two-hybrid assays. These results suggested that MdPYLs may bind to MdPP2C65 and MdPP2C72 in different manners and with different intensity. Our studies provide useful information for further investigating and researching the regulatory mechanisms of PYL family genes in response to abiotic stresses in the apple.
Highlights
Abscisic acid (ABA) is an important phytohormone involved in plant growth, plant development, and protection of plants against abiotic stresses [1,2]
Thirteen MdPYLs were identified in M. domestica genome
Phylogenetic reconstruction and gene structure analysis demonstrated that MdPYLs could be divided into four groups, and that they had similar gene structures and high conserved motifs in the same group
Summary
Abscisic acid (ABA) is an important phytohormone involved in plant growth, plant development, and protection of plants against abiotic stresses [1,2]. The core components of ABA signaling included the regulatory component of ABA receptors (PYLs), group A type 2C protein phosphatases (PP2Cs), and the sucrose nonfermenting 1-related protein kinases (SnRKs) [3,4,5,6]. PYLs, as ABA receptors, belong to the StAR-related lipid-transfer (START) superfamily containing a ligand-binding pocket enclosed by four conserved loops, CL1-CL4 [4,6], which is important in ABA signal transduction pathway. 14 PYLs containing the conserved structure have been recognized in the Arabidopsis genome [4,6,11], including AtPYR1 (Arabidopsis thaliana pyrabactin resistance1) and. Some PYLs, such as AtPYR1, AtPYL1, AtPYL2, and AtPYL3 inhibited PP2Cs in an ABA-dependent manner, while others including AtPYL4, AtPYL5, AtPYL6, AtPYL8, AtPYL9, AtPYL10, and AtPYL13 showed suppression of PP2Cs in the absence of ABA [10,12,13]
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