ClRTL1 Encodes a Chinese Fir RNase III-Like Protein Involved in Regulating Shoot Branching

The Developmental Delay of Seedlings With Cotyledons Only Confers Stress Tolerance to Suaeda aralocaspica (Chenopodiaceae) by Unique Performance on Morphology, Physiology, and Gene Expression

Cotyledons play an important role in seedling establishment, although they may just exist for a short time and become senescent upon the emergence of euphylla. So far, the detailed function of cotyledons has not been well understood. Suaeda aralocaspica is an annual halophyte distributed in cold deserts; its cotyledons could exist for a longer time, even last until maturity, and they must exert a unique function in seedling development. Therefore, in this study, we conducted a series of experiments to investigate the morphological and physiological performances of cotyledons under salt stress at different developmental stages. The results showed that the cotyledons kept growing slowly to maintain the normal physiological activities of seedlings by balancing phytohormone levels, accumulating osmoprotectants and antioxidants, and scavenging reactive oxygen species (ROS). Salt stress activated the expression of osmoprotectant-related genes and enhanced the accumulation of related primary metabolites. Furthermore, differentially expressed transcriptional profiles of the cotyledons were also analyzed by cDNA-AFLP to gain an understanding of cotyledons in response to development and salt stress, and the results revealed a progressive increase in the expression level of development-related genes, which accounted for a majority of the total tested TDFs. Meanwhile, key photosynthetic and important salt stress-related genes also actively responded. All these performances suggest that "big cotyledons" are experiencing a delayed but active developmental process, by which S. aralocaspica may survive the harsh condition of the seedling stage.

Screening and Validation of Housekeeping Genes of the Root and Cotyledon of Cunninghamia lanceolata under Abiotic Stresses by Using Quantitative Real-Time PCR

Cunninghamia lanceolata (Chinese fir) is a fast-growing and commercially important conifer of the Cupressaceae family. Due to the unavailability of complete genome sequences and relatively poor genetic background information of the Chinese fir, it is necessary to identify and analyze the expression levels of suitable housekeeping genes (HKGs) as internal reference for precise analysis. Based on the results of database analysis and transcriptome sequencing, we have chosen five candidate HKGs (Actin, GAPDH, EF1a, 18S rRNA, and UBQ) with conservative sequences in the Chinese fir and related species for quantitative analysis. The expression levels of these HKGs in roots and cotyledons under five different abiotic stresses in different time intervals were measured by qRT-PCR. The data were statistically analyzed using the following algorithms: NormFinder, BestKeeper, and geNorm. Finally, RankAggreg was applied to merge the sequences generated from three programs and rank these according to consensus sequences. The expression levels of these HKGs showed variable stabilities under different abiotic stresses. Among these, Actin was the most stable internal control in root, and GAPDH was the most stable housekeeping gene in cotyledon. We have also described an experimental procedure for selecting HKGs based on the de novo sequencing database of other non-model plants.

Comparative Analysis of the Chloroplast Genomic Information of Cunninghamia lanceolata (Lamb.) Hook with Sibling Species from the Genera Cryptomeria D. Don, Taiwania Hayata, and Calocedrus Kurz

Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) is an important coniferous tree species for timber production, which accounts for ~40% of log supply from plantations in southern China. Chloroplast genetic engineering is an exciting field to engineer several valuable tree traits. In this study, we revisited the published complete Chinese fir (NC_021437) and four other coniferous species chloroplast genome sequence in Taxodiaceae. Comparison of their chloroplast genomes revealed three unique inversions found in the downstream of the gene clusters and evolutionary divergence were found, although overall the chloroplast genomic structure of the Cupressaceae linage was conserved. We also investigated the phylogenetic position of Chinese fir among conifers by examining gene functions, selection forces, substitution rates, and the full chloroplast genome sequence. Consistent with previous molecular systematics analysis, the results provided a well-supported phylogeny framework for the Cupressaceae that strongly confirms the “basal” position of Cunninghamia lanceolata. The structure of the Cunninghamia lanceolata chloroplast genome showed a partial lack of one IR copy, rearrangements clearly occurred and slight evolutionary divergence appeared among the cp genome of C. lanceolata, Taiwania cryptomerioides, Taiwania flousiana, Calocedrus formosana and Cryptomeria japonica. The information from sequence divergence and length variation of genes could be further considered for bioengineering research.