Cotton fiber, a highly elongated, thickened single cell of the seed epidermis, is a powerful cell wall research model. Fiber length, largely determined during the elongation stage, is a key property of fiber quality. Several studies using expressed sequence tags and microarray analysis have identified transcripts that accumulate preferentially during fiber elongation. To further show the mechanism of fiber elongation, we used Digital Gene Expression Tag Profiling to compare transcriptome data from longer fiber chromosome introgressed lines (CSILs) containing segments of various Gossypium barbadense chromosomes with data from its recurrent parent TM-1 during fiber elongation (from 5 DPA to 20 DPA). A large number of differentially expressed genes (DEGs) involved in carbohydrate, fatty acid and secondary metabolism, particularly cell wall biosynthesis, were highly upregulated during the fiber elongation stage, as determined by functional enrichment and pathway analysis. Furthermore, DEGs related to hormone responses and transcription factors showed upregulated expression levels in the CSILs. Moreover, metabolic and regulatory network analysis indicated that the same pathways were differentially altered, and distinct pathways exhibited altered gene expression, in the CSILs. Interestingly, mining of upregulated DEGs in the introgressed segments of these CSILs based on D-genome sequence data showed that these lines were enriched in glucuronosyltransferase, inositol-1, 4, 5-trisphosphate 3-kinase and desulfoglucosinolate sulfotransferase activity. These results were similar to the results of transcriptome analysis. This report provides an integrative network about the molecular mechanisms controlling fiber length, which are mainly tied to carbohydrate metabolism, cell wall biosynthesis, fatty acid metabolism, secondary metabolism, hormone responses and Transcription factors. The results of this study provide new insights into the critical factors associated with cell elongation and will facilitate further research aimed at understanding the mechanisms underlying cotton fiber elongation.

Lagerstroemia indica is an important woody ornamental plant worldwide. However, the application of many technologies, such as transgenic breeding and genome editing, has been severely hampered due to the lack of efficient calli induction and regeneration technology. Here, we discussed a reliable and efficient calli induction and regeneration protocol using whole-leaf explants. This protocol’s effectiveness for the calli induction and regeneration systems in crape myrtle were up to 70.33% and 44.33%, respectively. Next, an efficient and stable Agrobacterium-mediated genetic transformation system was created from leaf calli, and the green fluorescent protein (GFP) was able to detect up to 90% of its positive frequency. Meanwhile, two positive lines’ transfer DNA insertion sites and directions were identified using whole genome sequencing. LiMYB75, a novel R2R3-MYB transcription factor, was identified and transferred to the L. indica genome to enhance the leaf calli regeneration frequency. Surprisingly, overexpressing LiMYB75 increased the frequency of calli regeneration in the leaf by 1.27 times and the number of regenerated plantlets per callus by 4.00 times compared to the wild type, by regulating the expression levels of genes involved in callus formation, such as SHOOT MERISTEMLESS (STM). Overall, our findings revealed a simple, reliable, and highly efficient transformation approach and identified the desirable candidate gene LiMYB75, which improves L. indica’s calli regeneration efficiency.

Catalpa bungei is an economically important tree with high-quality wood, which is highly ornamentally valuable in China. Salinity is one of the major constraints restricting the growth of the C. bungei. However, the molecular mechanism underlying the salt stress response remains unknown in C. bungei. In our previous study, a novel WRKY transcription factor gene CbWRKY27 was isolated using association mapping based on the transcriptome database of Catalpa Yuqiu1. In this study, CbWRKY27 was found to function as a transcriptional activator in the nucleus. The transcription of CbWRKY27 was inhibited under salt stress and reactive oxygen species (ROS) but was induced after abscisic acid (ABA) treatment. CbWRKY27-overexpression plants showed decreased tolerance to salt stress compared to wild type while enhancing sensitivity to ABA-regulated lateral root length. Quantitative real-time PCR (qPCR) studies showed that the transcript levels of the ABA biosynthesis gene (NCED3), signaling genes (ABI3 and ABI5), and responsive genes (RD29B and RD22) were greatly increased in CbWRKY27-overexpression plants under salt stress. Under salt treatment, CbWRKY27-overexpression plants disturbed ROS homeostasis by repressing antioxidant enzymes and enhancing the production of O₂⁻ and H₂O₂ through down-regulation of ROS-scavenging-related genes (APX, SOD, and PER57). In summary, these results indicate that CbWRKY27 negatively regulates salt tolerance in C. bungei.