Abstract
The Ca2+/cation antiporters (CaCA) superfamily proteins play vital function in Ca2+ ion homeostasis, which is an important event during development and defense response. Molecular characterization of these proteins has been performed in certain plants, but they are still not characterized in Triticum aestivum (bread wheat). Herein, we identified 34 TaCaCA superfamily proteins, which were classified into TaCAX, TaCCX, TaNCL, and TaMHX protein families based on their structural organization and evolutionary relation with earlier reported proteins. Since the T. aestivum comprises an allohexaploid genome, TaCaCA genes were derived from each A, B, and D subgenome and homeologous chromosome (HC), except chromosome-group 1. Majority of genes were derived from more than one HCs in each family that were considered as homeologous genes (HGs) due to their high similarity with each other. These HGs showed comparable gene and protein structures in terms of exon/intron organization and domain architecture. Majority of TaCaCA proteins comprised two Na_Ca_ex domains. However, TaNCLs consisted of an additional EF-hand domain with calcium binding motifs. Each TaCaCA protein family consisted of about 10 transmembrane and two α-repeat regions with specifically conserved signature motifs except TaNCL, which had single α-repeat. Variable expression of most of the TaCaCA genes during various developmental stages suggested their specified role in development. However, constitutively high expression of a few genes like TaCAX1-A and TaNCL1-B indicated their role throughout the plant growth and development. The modulated expression of certain genes during biotic (fungal infections) and abiotic stresses (heat, drought, salt) suggested their role in stress response. Majority of TaCCX and TaNCL family genes were found highly affected during various abiotic stresses. However, the role of individual gene needs to be established. The present study unfolded the opportunity for detail functional characterization of TaCaCA proteins and their utilization in future crop improvement programs.
Highlights
Calcium ion (Ca2+) is a vital element in plants due to its roles as an essential nutrient and secondary messenger (Hirschi, 2004; Case et al, 2007)
The identified Ca2+/cation antiporters (CaCAs) superfamily proteins were further classified into cation exchanger (CAX), cation/Ca2+ exchanger (CCX), Mg2+/H+ exchanger (MHX), and NCX like protein (NCL) protein groups based on their relative sequence homology with known sequences from Arabidopsis and rice
A total of 34 TaCaCA superfamily proteins were identified in T. aestivum genome by extensive BLAST search of known sequences from rice and Arabidopsis (File S1)
Summary
Calcium ion (Ca2+) is a vital element in plants due to its roles as an essential nutrient and secondary messenger (Hirschi, 2004; Case et al, 2007). The NCL proteins are reported as a new member of CaCA superfamily (Wang et al, 2012), separated from CAX family due to the presence of long cytoplasmic loop with EF-hand domains (Emery et al, 2012; Pittman and Hirschi, 2016a) These are identified in numerous land plants, and AtNCL is reported to perform Na+/Ca2+exchange activity (Emery et al, 2012; Li et al, 2016). The present study provided inclusive information about TaCaCA superfamily proteins that would be very useful in future crop development programs
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