Differentiation of Cold Tolerance in an Artificial Population of a Mangrove Species, Kandelia obovata, Is Associated With Geographic Origins

The complete mitochondrial genome of the Kandelia obovata Sheue, H.Y.Liu & J.W.H.Yong (Rhizophoraceae)

Kandelia obovata Sheue, H.Y.Liu & J.W.H.Yong is one of the most cold-resistant true mangrove species, and it is widely distributed from the South China Sea to southern Japan. In the current study, the complete mitochondrial genome sequence of K. obovata was assembled using Illumina reads. It is the first mitochondrial genome of the Kandelia genus within the family Rhizophoraceae to be sequenced. The mitochondrial genome size is 312,146 bp with a total of 49 predicted genes, including 29 protein-coding genes, 17 transfer RNA genes, and 3 ribosomal RNA genes. The overall GC content of the genome is 41.87%. A phylogenetic tree constructed using nine complete mitochondrial genomes revealed that K. obovata is more closely related to Bruguiera species. This study enriches the plastid genome of Kandelia, furnishing valuable genetic insights for the investigation of evolutionary and population genetics in Kandelia and other mangrove species.

Comprehensive analysis of the NAC transcription factor gene family in Kandelia obovata reveals potential members related to chilling tolerance

BACKGROUND

Kandelia obovata is an important mangrove species extensively distributed in Eastern Asia that is susceptible to low-temperature stress. NAC (NAM, ATAF1/2 and CUC2) domain proteins are transcription factors (TFs) that play various roles in plant growth and development and in the plant response to environmental stresses. Nevertheless, genome-wide analyses of K. obovata NAC genes (KoNACs) and their responses to chilling stress have rarely been studied.

METHODS

The KoNAC gene family was identified and characterized using bioinformatic analysis, the subcellular location of some NAC proteins was confirmed using confocal microscopy analysis, and the KoNACs that responded to chilling stress were screened using RNA-seq and qRT-PCR analysis.

RESULTS

A total of 79 KoNACs were identified, and they were unequally distributed across all 18 chromosomes of K. obovata. The KoNAC proteins could be divided into 16 subgroups according to the phylogenetic tree based on NAC family members of Arabidopsis thaliana. The KoNACs exhibited greater synteny with A. thaliana sequences than with Oryza sativa sequences, indicating that KoNACs underwent extensive evolution after the divergence of dicotyledons and monocotyledons. Segmental duplication was the main driving force of the expansions of KoNAC genes. Confocal microscopy analysis verified that the four randomly selected KoNACs localized to the nucleus, indicating the accuracy of the bioinformatic predictions. Tissue expression pattern analysis demonstrated that some KoNAC genes showed tissue-specific expression, suggesting that these KoNACs might be important for plant development and growth. Additionally, the expression levels of 19 KoNACs were significantly (15 positively and 4 negatively) induced by cold treatment, demonstrating that these KoNACs might play important roles during cold stress responses and might be candidate genes for the genetic engineering of K. obovata with enhanced chilling stress tolerance. Coexpression network analysis revealed that 381 coexpressed pairs (between 13 KoNACs and 284 other genes) were significantly correlated.

CONCLUSIONS

Seventy-nine KoNACs were identified in K. obovata, nineteen of which displayed chilling-induced expression patterns. These genes may serve as candidates for functional analyses of KoNACs engaged in chilling stress. Our results lay the foundation for evolutionary analyses of KoNACs and their molecular mechanisms in response to environmental stress.