Abstract
HD-ZIP is a unique type of transcription factor in plants, which are closely linked to the regulation of plant growth and development, the response to abiotic stress, and disease resistance. However, there is little known about the HD-ZIP gene family of pepper. In this study, 40 HD-ZIP family members were analyzed in the pepper genome. The analysis indicated that the introns number of Ca-HD-ZIP varied from 1 to 17; the number of amino acids was between 119 and 841; the theoretical isoelectric point was between 4.54 and 9.85; the molecular weight was between 14.04 and 92.56; most of them were unstable proteins. The phylogenetic tree divided CaHD-ZIP into 4 subfamilies; 40 CaHD-ZIP genes were located on different chromosomes, and all of them contained the motif 1; two pairs of CaHD-ZIP parallel genes of six paralogism genes were fragment duplications which occurred in 58.28~88.24 million years ago. There were multiple pressure-related action elements upstream of the start codon of the HD-Z-IP family. Protein interaction network proved to be coexpression phenomenon between ATML1 (CaH-DZ22, CaHDZ32) and At4g048909 (CaHDZ12, CaHDZ31), and three regions of them were highly homology. The expression level of CaHD-ZIP gene was different with tissues and developmental stages, which suggested that CaHD-ZIP may be involved in biological functions during pepper progress. In addition, Pepper HD-ZIP I and II genes played a major role in salt stress. CaHDZ03, CaHDZ 10, CaHDZ17, CaHDZ25, CaHDZ34, and CaHDZ35 were significantly induced in response to salt stress. Notably, the expression of CaHDZ07, CaHDZ17, CaHDZ26, and CaHDZ30, homologs of Arabidopsis AtHB12 and AtHB7 genes, was significantly upregulated by salt stresses. CaHDZ03 possesses two closely linked ABA action elements, and its expression level increased significantly at 4 h under salt stress. qRT-P-CR and transcription analysis showed that the expression of CaHDZ03 and CaHDZ10 was upregulated under short-term salt stress, but CaHDZ10 was downregulated with long-term salt stress, which provided a theoretical basis for research the function of Ca-HDZIP in response to abiotic stress.
Highlights
Plant transcription factors can be divided into 58 families according to the conserved domain and function [1]
Analysis of the predicted introns and exons of the pepper HD-ZIP gene revealed that 5 genes (CaHDZ 03, CaHDZ17, CaHDZ23, CaHDZP35, and CaHDZ38) had no introns in the pepper genome
HDZ proteins of pepper can be divided into four categories (HD-ZIP I-IV), and the number of HD-ZIP I, II, III, and IV are 14, 10, and 5, respectively, 11, and 17, 10, 5, and 16 in Arabidopsis [58]; 12, 9, 4, and 7 in physic nut [59]; 11, 7, 5, and 8 in grape [60]; 16, 10, 9, and 10 in sesame [53]. These results suggested that the HD-ZIPI protein was the most abundant type of pepper HD-ZIP transcription factor, and the amount of HD-ZIPIII protein in pepper was the same as that of most plants
Summary
Plant transcription factors can be divided into 58 families according to the conserved domain and function [1]. Homeobox (HB) protein is a kind of transcription factor closely related to biological growth and development [2]. HD-ZIP transcription factor is a unique transcription factor in plants and plays roles in the growth, development, disease resistance, and abiotic stress [6]. These functions of HB have been reported in mass [7], ferns [8], monocotyledons [9], and dicotyledons [10, 11]. According to structure and function, HD-ZIP proteins can be divided into four subfamilies: HD-ZIP I, HD-ZIP II, HD-ZIP III, and HD-ZIP IV [13]
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