Gene Expression and Physiological Analyses Provide New Insights Toward Adventitious Rooting in Yellow Camellia (C. nitidissima)

Yellow-flowering camellias are rare and endangered shrubs or small trees. Due to the limited access to seeds, clonal propagation via stem cutting is the commonly used method. Although adventitious root formation is essential for cuttings to survive, this process is complex and has not been molecularly studied in a yellow camellia species. This study aimed to identify yellow camellia candidate genes involved in adventitious root development by de novo assembly of publicly available RNA-sequencing (RNA-seq) reads from leaf, flower, fruit, and root of Camellia nitidissima . Also known as Camellia chrysantha , C. nitidissima is one of the most well-known yellow camellia species. A group of 310 transcript isoforms was annotated to be auxin responsive, representing 50 genes. Many of these genes are known to be involved in adventitious root development in other species. Quantitative reverse-transcriptase polymerase chain reaction (RT-qPCR) analyses of some known rooting genes revealed their differential expression among different tissue types and during adventitious root development in C. nitidissima cuttings. Notably, AGO1 , ANT , ARF8 , GH3.5 , and GH3.6 displayed a higher expression in adventitious roots than in other tissue types. During adventitious root development, the expression of both IAR4 and PP2A increased after 0 day in the basal part of cuttings, except at 27 days after excision. Although the expression of ANT was the highest on 0 day, it exhibited an increasing trend as adventitious roots developed. In addition, our study showed that leaf tissue contained the highest level of hydrogen peroxide, followed by flower and stem. Their peroxidase activity displayed the opposite trend. C. nitidissima cuttings contained a similar level of lignin per dry weight to easy-to-root poplar cuttings, with a closed and lignified cork structure, which may interfere with the emergence of adventitious roots. The study provides the first insights into a yellow camellia’s potential rooting genes and advances the understanding of adventitious rooting.