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Zhigang Ouyang, Huihui Duan, Lanfang Mi, Wei Hu, Jianmei Chen, Xingtao Li and Balian Zhong

In eukaryotic systems, messenger RNA regulations, including splicing, 3′-end formation, editing, localization, and translation, are achieved by different RNA-binding proteins and noncoding RNAs. The YTH domain is a newly identified RNA-binding domain that was identified by comparing its sequence with that of splicing factor YT521-B. Previous study showed that the YTH gene plays an important role in plant resistance to abiotic and biotic stress. In this study, 211 YTH genes were identified in 26 species that represent four major plant lineages. Phylogenetic analysis revealed that these genes could be divided into eight subgroups. All of the YTH genes contain a YT521 domain and have different structures. Ten YTH genes were identified in navel orange (Citrus sinensis). The expression profiles of these CitYTH genes were analyzed in different tissues and at different fruit developmental stages, and CitYTH genes displayed distinct expression patterns under heat, cold, salt, and drought stress. Furthermore, expression of the CitYTH genes in response to exogenous hormones was measured. Nuclear localization was also confirmed for five of the proteins encoded by these genes after transient expression in Nicotiana benthamiana cells. This study provides valuable information on the role of CitYTHs in the signaling pathways involved in environmental stress responses in Citrus.

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Yi-Xuan Kou, Hui-Ying Shang, Kang-Shan Mao, Zhong-Hu Li, Keith Rushforth and Robert P. Adams

Leyland cypress [×Hesperotropsis leylandii (A.B. Jacks. & Dallim.) Garland & G. Moore, Cupressaceae] is a well-known horticultural evergreen conifer in the United Kingdom, United States, Australia, New Zealand, and other countries. As demonstrated by previous studies, this taxon is a hybrid between alaska (nootka) cypress [Callitropsis nootkatensis (D. Don) Oerst. ex D.P. Little] and monterey cypress [Hesperocyparis macrocarpa (Hartw. ex Gordon) Bartel]. However, the genetic background of leyland cypress cultivars is unclear. Are they F1 or F2 hybrids or backcrosses? In this study, six individuals that represent major leyland cypress cultivars and two individuals each of its two putative parental species were collected, and three nuclear DNA regions (internal transcribed spacer, leafy and needly), three mitochondrial (mt) DNA regions (coxI, atpA, and rps3), and two chloroplast (cp) DNA regions (matK and rbcL) were sequenced and analyzed. Sequencing results of nuclear DNA regions revealed that leyland cypress cultivars consist of putative F1 and F2 hybrids as well as backcrosses. Analysis of the cp and mt DNA from six cultivars of leyland cypress revealed that their cytoplasmic (cp and mt) genomes came from alaska cypress. Our findings will provide important instructions and background knowledge on the management of these major leyland cypress cultivars as well as future studies. Meanwhile, alaska cypress and monterey cypress may have diverged with each other ≈46 million years ago. The fact that they can produce fertile hybrids indicates that hybridization events may have played an important role in the evolutionary history of the cypress family (Cupressaceae).