Molecular characterization and transcriptome profiling of expansin genes isolated from Calotropis procera fibers

Hafiza Masooma Naseer Cheema¹ · Aftab Bashir^*2· Asia Khatoon² · Nadia Iqbal² · Yusuf Zafar² · Kauser A. Malik³ 

¹University of Agriculture, Faisalabad, Pakistan
²National Institute for Biotechnology and Genetic Engineering, Jhang Road Faisalabad, Pakistan
³Department of Biological Sciences, F.C. College University, Lahore, Pakistan

*Corresponding author: aftabbashir@nibge.org

Financial support: This study was supported by a grant from Ministry of Food and Agriculture (MinFA). Partial support was provided by the PhD student grants from Higher Education Commission of Pakistan (HEC) for the PhD program carried out by Hafiza Masooma Naseer Cheema and Nadia Iqbal at NIBGE.

Keywords: Calotropis procera, cDNA library, cotton fibers, EXPANSIN A, signal peptide, transcriptome profiling.

The Calotropis procera seed fibers provide an excellent model system to study the genes involved in fiber elongation, fineness and strength. Expansins constitute one of the important gene families involved in plant cell expansion and other cell wall modification processes. Four homologs of Expansin A gene i.e. CpEXPA1, CpEXPA2, CpEXPA3 and CpEXPA4 were isolated from the cDNA library obtained from fast growing Calotropis procera fibers. These homologs represented typical Expansin A family. Each of them had two conserved domains including GH45 like domain and the putative polysaccharide binding domain. The deduced amino acid sequences of the homologs indicated three conserved motifs: i) eight cysteine residues at N-terminus, ii) four tryptophan residues at C-terminus and iii) a Histidine-Phenylalanine-Aspartate motif in the center of the sequence. The presence of N-terminal signal peptide consisting of hydrophobic amino acids and a transmembrane region in all these expansin isoforms suggests their cotranslational insertion into the endoplasmic reticulum and then transportation to the cell wall by secretory pathway. The relative quantification of the four expansins in root, stem, fiber and leave tissues indicated that the transcripts of CpEXPA1, CpEXPA2, CpEXPA3 and CpEXPA4 are variably transcribed in these tissues. The lowest transcription of all the four Expansin A isoforms was observed in elongating roots indicating that root tissue might be having specific expansins other than those confined to air grown organs.