Abstract
Considering the known effects of xyloglucan endotransglycosylase (XET) on plant growth and development, we aimed to determine whether XETs help to regulate the growth and elongation of Huangguogan shoots and roots. We confirmed a possible role for XET during seedling etiolation. Our results revealed that the roots of etiolated seedlings (H-E) were longer than those of green seedlings (H-G). However, shoot length exhibited the opposite pattern. We also observed positive and negative effects on the xyloglucan-degrading activity of XET in the root sub-apical region and shoots of etiolated Huangguogan seedling, respectively. There was a significant down-regulation in CitXET expression in the etiolated shoots at 15 days after seed germination. On the contrary, it was significantly increased in the root sub-apical region of etiolated and multicolored seedlings at 15 days after seed germination. The XET coding sequence (i.e., CitXET) was cloned from Huangguogan seedlings using gene-specific primers. The encoded amino acid sequence was predicted by using bioinformatics-based methods. The 990-bp CitXET gene was highly homologous to other XET genes. The CitXET protein was predicted to contain 319 amino acids, with a molecular mass of 37.45 kDa and an isoelectric point of 9.05. The predicted molecular formula was C1724H2548N448O466S14, and the resulting protein included only one transmembrane structure. The CitXET secondary structure consisted of four main structures (i.e., 21% α-helix, 30.72% extended strand, 9.09% β-turn, and 39.18% random coil). Analyses involving the NCBI Conserved Domains Database (NCBI-CDD), InterPro, and ScanProsite revealed that CitXET was a member of the glycosyl hydrolase family 16 (GH16), and included the DEIDFEFLG motif. Our results indicate that the differed degrees of etiolation influenced the CitXET expression pattern and XET activity in Huangguogan seedlings. The differential changes in XET activity and CitXET expression levels in Huangguogan seedlings may influence the regulation of root and shoot development, and may be important for seedling etiolation.
Highlights
The genus Citrus of the family Rutaceae includes commercially important and widely cultivated fruit species [1]
Our results indicate that the degree of etiolation affects the xyloglucan endotransglycosylase (XET) activity and citrus XET gene (CitXET) expression patterns of Huangguogan seedlings
The 960-bp CitXET coding sequence encodes a protein consisting of 319 amino acids
Summary
The genus Citrus of the family Rutaceae includes commercially important and widely cultivated fruit species [1]. The leaves of etiolated seedlings do not turn green even at 20 days after seed germination, and even death after further 10 days. We found that etiolation decreased the leaf area and reduced the optical area, resulting in dwarf plants and weakening growth potential [2]. After seed germinating in darkness, seedlings undergo etiolated growth (i.e., skotomorphogenesis), and leaf color is dependent on carotenoids. This developmental step is characterized by a rapid elongation of the hypocotyl topped by a hook with underdeveloped cotyledons [3]. Etiolation decreases the leaf area, causes dwarfism in plants, lowers the growth potential, and may even cause to death. Over the past two decades, the growth and development of etiolated plants have been studied in terms of light regulation [4], endogenous abscisic acid [3], ethylene responses [5], phospholipid hydroperoxide glutathione peroxidase [6], riboflavin biosynthesis [7], and the proteome [8]
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