Genome-Wide Identification and Characterization of CPR5 Genes in Gossypium Reveals Their Potential Role in Trichome Development

Recent genome resequencing paraded COBRA-Like gene family roles in abiotic stress and wood formation in Poplar

A cell wall determines the mechanical properties of a cell, serves as a barrier against plant stresses, and allows cell division and growth processes. The COBRA-Like (COBL) gene family encodes a putative glycosylphosphatidylinositol (GPI)-anchored protein that controls cellulose deposition and cell progression in plants by contributing to the microfibril orientation of a cell wall. Despite being studied in different plant species, there is a dearth of the comprehensive global analysis of COBL genes in poplar. Poplar is employed as a model woody plant to study abiotic stresses and biomass production in tree research. Improved genome resequencing has enabled the comprehensive exploration of the evolution and functional capacities of PtrCOBLs (Poplar COBRA-Like genes) in poplar. Phylogeny analysis has discerned and classified PtrCOBLs into two groups resembling the Arabidopsis COBL family, and group I genes possess longer proteins but have fewer exons than group II. Analysis of gene structure and motifs revealed PtrCOBLs maintained a rather stable motif and exon-intron pattern across members of the same group. Synteny and collinearity analyses exhibited that the evolution of the COBL gene family was heavily influenced by gene duplication events. PtrCOBL genes have undergone both segmental duplication and tandem duplication, followed by purifying selection. Promotor analysis flaunted various phytohormone-, growth- and stress-related cis-elements (e.g., MYB, ABA, MeJA, SA, AuxR, and ATBP1). Likewise, 29 Ptr-miRNAs of 20 families were found targeting 11 PtrCOBL genes. PtrCOBLs were found localized at the plasma membrane and extracellular matrix, while gene ontology analysis showed their involvement in plant development, plant growth, stress response, cellulose biosynthesis, and cell wall biogenesis. RNA-seq datasets depicted the bulk of PtrCOBL genes expression being found in plant stem tissues and leaves, rendering mechanical strength and rejoinders to environmental cues. PtrCOBL2, 3, 10, and 11 manifested the highest expression in vasculature and abiotic stress, and resemblant expression trends were upheld by qRT-PCR. Co-expression network analysis identified PtrCOBL2 and PtrCOBL3 as hub genes across all abiotic stresses and wood developing tissues. The current study reports regulating roles of PtrCOBLs in xylem differentiating tissues, tension wood formation, and abiotic stress latency that lay the groundwork for future functional studies of the PtrCOBL genes in poplar breeding.

Histone Maps in Gossypium darwinii Reveal Epigenetic Regulation Drives Subgenome Divergence and Cotton Domestication

The functional annotation of genomes, including chromatin modifications, is essential to understand the intricate architecture of chromatin and the consequential gene regulation. However, such an annotation remains limited for cotton genomes. Here, we conducted chromatin profiling in a wild allotetraploid cotton Gossypium darwinii (AD genome) by integrating the data of histone modification, transcriptome, and chromatin accessibility. We revealed that the A subgenome showed a higher level of active histone marks and lower level of repressive histone marks than the D subgenome, which was consistent with the expression bias between the two subgenomes. We show that the bias in transcription and histone modification between the A and D subgenomes may be caused by genes unique to the subgenome but not by homoeologous genes. Moreover, we integrate histone marks and open chromatin to define six chromatin states (S1-S6) across the cotton genome, which index different genomic elements including genes, promoters, and transposons, implying distinct biological functions. In comparison to the domesticated cotton species, we observed that 23.2% of genes in the genome exhibit a transition from one chromatin state to another at their promoter. Strikingly, the S2 (devoid of epigenetic marks) to S3 (enriched for the mark of open chromatin) was the largest transition group. These transitions occurred simultaneously with changes in gene expression, which were significantly associated with several domesticated traits in cotton. Collectively, our study provides a useful epigenetic resource for research on allopolyploid plants. The domestication-induced chromatin dynamics and associated genes identified here will aid epigenetic engineering, improving polyploid crops.

Genome-wide analysis of IQD proteins and ectopic expression of watermelon ClIQD24 in tomato suggests its important role in regulating fruit shape

The plant-specific IQ67 domain (IQD) is the largest class of calmodulin targets found in plants, and plays an important role in many biological processes, especially fruit development processes. However, the functional role of IQD proteins in the development of watermelon (Citrullus lanatus) shape remains unknown, as the IQD protein family in watermelon has not been systematically characterized. Herein, we elucidated the gene structures, chromosomal locations, evolutionary divergence, and functions of 35 IQD genes in the watermelon genome. The transcript profiles and quantitative real-time PCR analysis at different stages of fruit development showed that the ClIQD24 gene was highly expressed on 0 days after pollination. Furthermore, we found that the ectopic overexpression of ClIQD24 promoted tomato fruit elongation, thereby revealing the significance of ClIQD24 in the progression of watermelon shape. Our study will serve as a reference for further investigations on the molecular mechanisms underlying watermelon fruit shape formation.