Abstract
BackgroundSomatic embryogenesis receptor-like kinases (SERKs) are leucine-rich repeat receptor-like kinases associated with various signaling pathways. These kinases have a relationship with stress signals, and they are also believed to be important for regulating plant growth. However, information about this protein family in apple is limited.ResultsTwelve apple SERK genes distributed across eight chromosomes were identified. These genes clustered into three distinct groups in a phylogenetic analysis. All of the encoded proteins contained typical SERK domains. The chromosomal locations, gene/protein structures, synteny, promoter sequences, protein–protein interactions, and physicochemical characteristics of MdSERK genes were analyzed. Bioinformatics analyses demonstrated that gene duplications have likely contributed to the expansion and evolution of SERK genes in the apple genome. Six homologs of SERK genes were identified between apple and Arabidopsis. Quantitative real-time PCR analyses revealed that the MdSERK genes showed different expression patterns in various tissues. Eight MdSERK genes were responsive to stress signals, such as methyl jasmonate, salicylic acid, abscisic acid, and salt (NaCl). The application of exogenous brassinosteroid and auxin increased the growth and endogenous hormone contents of Malus hupehensis seedlings. The expression levels of seven MdSERK genes were significantly upregulated by brassinosteroid and auxin. In addition, several MdSERK genes showed higher expression levels in standard trees of ‘Nagafu 2’ (CF)/CF than in dwarf trees of CF/‘Malling 9’ (M.9), and in CF than in the spur-type bud mutation “Yanfu 6” (YF).ConclusionThis study represents the first comprehensive investigation of the apple SERK gene family. These data indicate that apple SERKs may function in adaptation to adverse environmental conditions and may also play roles in controlling apple tree growth.
Highlights
Somatic embryogenesis receptor-like kinases (SERKs) are leucine-rich repeat receptor-like kinases associated with various signaling pathways
All MdSERK proteins were hydrophilic according to their grand average of hydropathicity (GRAVY) values
The application of exogenous BR and auxin in separate experiments increased endogenous BR and Indole-3-acetic acid (IAA) contents (Fig. 8), and induced horizontal and vertical growth of the stem (Fig. 9). These results indicate that there may be a complicated mechanism by which auxin regulates somatic embryogenesis receptor-like kinases (SERKs) genes in apple, and that these MdSERK genes might have a positive role in regulating apple tree growth by mediating BR and auxin signals
Summary
Somatic embryogenesis receptor-like kinases (SERKs) are leucine-rich repeat receptor-like kinases associated with various signaling pathways These kinases have a relationship with stress signals, and they are believed to be important for regulating plant growth. As receptors for diverse signals (i.e., brassinosteroid (BR) signals, flagellin signals, male sporogenesis, and Mi-1-mediated resistance to potato aphids), SERK proteins mainly localize in the cell membrane [10]. They contain seven conserved domains: a signal peptide (SP) domain; a leu-zipper (ZIP) domain; five Leu-rich repeat (LRR) domains; a Ser-Pro-rich (SPP) domain; a transmembrane (TM) domain; and a cytoplasmic Ser/Thr kinase domain adjacent to the C-terminal domain (CTD) [11].
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