The GLK gene family plays a crucial role in the regulation of chloroplast development and participates in chlorophyll synthesis. However, the precise mechanism by which GLK contributes to citrus’s chlorophyll synthesis remains elusive. The GLK gene family causes variations in the photosynthetic capacity and chlorophyll synthesis of different citrus varieties. In this study, we identified tissue-specific members and the key CcGLKs involved in chlorophyll synthesis. A total of thirty CcGLK transcription factors (TFs) were discovered in the citrus genome, distributed across all nine chromosomes. The low occurrence of gene tandem duplication events and intronic variability suggests that intronic variation may be the primary mode of evolution for CcGLK TFs. Tissue-specific expression patterns were observed for various GLK family members; for instance, CcGLK12 and CcGLK15 were specifically expressed in the skin, while CcGLK30 was specific to the ovary, and CcGLK10, CcGLK6, CcGLK21, CcGLK2, CcGLK18, CcGLK9, CcGLK28, and CcGLK8 were specifically expressed in the leaves. CcGLK4, CcGLK5, CcGLK11, CcGLK23, CcGLKl7, CcGLK26, and CcGLK20 may participate in the regulation of the ALA, prochlorophylate, protoporphyrin IX, Mg-protoporphyrin IX, Chl b, T-Chl, MG-ProtoIX ME, and POR contents in citrus.
Abstract Tamias sibiricus is regarded as one predominant scatter-hoarder that stores their food items both in small scattered caches and underground larder-hoards. This unique behavior, though providing essential seed dispersal services for many plant species worldwide, relies highly on accurate spatial memory and acute sense of olfaction. Here, we assembled a chromosome-scale genome of T. sibiricus using Illumina sequencing, PacBio sequencing and chromosome structure capture technique. The genome was 2.64 Gb in size with scaffold N50 length of 172.61 Mb. A total of 2.59 Gb genome data was anchored and orientated onto 19 chromosomes (ranging from 28.70 to 222.90 Mb) with a mounting rate of up to 98.03%. Meanwhile, 25,311 protein-coding genes were predicted with an average gene length of 32,936 bp, and 94.73% of these genes were functionally annotated. This reference genome will be a valuable resource for in-depth studies on basic biological possess and environmental adaptation of the Siberian chipmunk, as well as promoting comparative genomic analyses with other species within Rodentia.
Xyloglucan endotransglycosylase (XET) genes are widely distributed in most plants, but the codon usage bias of XET genes has remained uncharacterized. Thus, we analyzed the codon usage bias using 4500 codons of 20 XET genes to elucidate the genetic and evolutionary patterns. Phylogenetic and hierarchical cluster analyses revealed that the 20 XET genes belonged to two groups. The closer the genetic distance, the more similar the codon usage preference. The codon usage bias of most XET genes was weak, but there was also some codon usage bias. AGA, AGG, AUC, and GUG were the top four codons (RSCU > 1.5) in the 20 XET genes. CitXET had a stronger codon usage bias, and there were eight optimal codons of CitXET (i.e., AGA, AUU, UCU, CUU, CCA, GCU, GUU, and AAA). The RSCU values underwent a correspondence analysis. The two main factors affecting codon usage bias (i.e., Axes 1 and 2) accounted for 54.8% and 17.6% of the total variation, respectively. Multiple correspondence analysis revealed that XET genes were widely distributed, with Group 1 genes being closer to Axis 1 than Group 2 genes, which were closer to Axis 2. Codons with A/U at the third codon position were distributed closer to Axis 1 than codons with G/C at the third codon position. PgXET, ZmXET, VlXET, VrXET, and PcXET were biased toward codons ending with G/C. In contrast, CitXET, DpXET, and BrpXET were strongly biased toward codons ending with A/U, indicating that these XET genes have a strong codon usage bias. Translational selection and base composition (especially A and U at the third codon position), followed by mutation pressure and natural selection, may be the most important factors affecting codon usage of 20 XET genes. These results may be useful in clarifying the codon usage bias of XET genes and the relevant evolutionary characteristics.
The key pigment substances and genes associated to the orange color in mandarin citrus Shiranui peel and the citrine/yellow peel of its mutant Citrine Shiranui. Eleven carotenoids were detected by LC-MS/MS. β-Cryptoxanthin increased during fruit ripening, but the increase was significantly small in Citrine Shirnaui. As a result, in full-colored fruits β-cryptoxanthin made up 43.62% in peel of Shiranui but only 8.21% in Citrine Shiranui. Chlorophylls degraded during fruit ripening, but in Citrine Shiranui peel it was kept for more. There are 21 and 10 genes were enriched in carotenoid biosynthesis pathway and chlorophyll degradation pathway respectively from RNA-sequencing results. The expressions of CitBCH2 and CitNCY1 might connect with lower β-cryptoxanthin synthesis and higher chlorophyll degradation in Citrine Shiranui. Dual-Luciferase Reporter Assay (LUC) indicated that an ethylene-related ERF transcription factor (CitEFR5) and an abscisic acid (ABA)‐RESPONSIVE ELEMENT‐BINDING FACTOR 2 (CitABF2) positively regulated CitBCH2 and CitNCY1 respectively. In summary, the citrine/yellow color in Citrine Shiranui peel that different from the orange peel of Shiranui might attribute to the difference of ethylene and ABA signals-triggered carotenoid biosynthesis and chlorophyll degradation between the two citruses.
AP2/ERF (APETALA2/ethylene responsive factor) is a family of plant-specific transcription factors whose members are widely involved in many biological processes, such as growth, development, and biotic and abiotic stress responses. Here, 20 AP2/ERF genes were identified based on wheat RNA-seq data before and after drought stress, and classified as AP2, ERF, DREB, and RAV. The analysis of gene structure revealed that about 85% of AP2/ERF family members had lost introns, which are presumed to have been lost during the formation and evolution of the wheat genome. The expression of 20 AP2/ERF family genes could be verified by qRT-PCR, which further supported the validity of the RNA-seq data. Subsequently, subcellular localization and transcriptional activity experiments showed that the ERF proteins were mainly located in the nucleus and were self-activating, which further supports their functions as transcription factors. Furthermore, we isolated a novel ERF gene induced by drought, salt, and cold stresses and named it TaERF-6-3A. TaERF-6-3A overexpression increased sensitivity to drought and salt stresses in Arabidopsis, which was supported by physiological and biochemical indices. Moreover, the expression of stress- and antioxidant-related genes was downregulated in TaERF-6-3A-overexpressing plants. Overall, these results contribute to the further understanding of the TaERF-6-3A gene function in wheat.
Organic acids are a major index of fresh fruit marketing properties. However, the genetic effects on the organic acid level in postharvest citrus fruit still remain unknown. Here, we used the fruits of about 40 lines in a hybrid population (high-acid "HB Pumelo" × low-acid "Fairchild") to analyze the organic acid metabolism of postharvest citrus fruit. A transgressive content of titratable acid (TA) was observed, which was attributed to citrate accumulation. High- and low-acid fruits (No. 130, 168 and No. 080, 181, respectively) were chosen for further study. Gene expression analysis on citrate metabolism showed that the high accumulation of citrate could be attributed to the low activity of γ-aminobutyric acid (GABA) shunt, and was partially due to the block of tricarboxylic acid (TCA) cycle by low mitochondrial aconitase (m-ACO) expression. TA level was significantly negatively correlated with weight loss in fruits during postharvest storage, implying a close relationship between organic acid and water metabolism.
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