Li Chen’s research while affiliated with Xinjiang Agricultural University and other places

Lettuce is susceptible to high-temperature stress during cultivation, leading to bolting and affecting yield. Plant-specific transcription factors, known as GRAS proteins, play a crucial role in regulating plant growth, development, and abiotic stress responses. In this study, the entire lettuce LsGRAS gene family was identified. The results show that 59 LsGRAS genes are unevenly distributed across the nine chromosomes. Additionally, all LsGRAS proteins showed 100% nuclear localization based on the predicted subcellular localization and were phylogenetically classified into nine conserved subfamilies. To investigate the expression profiles of these genes in lettuce, we analyzed the transcription levels of all 59 LsGRAS genes in the publicly available RNA-seq data under the high-temperature treatment conducted in the presence of exogenous melatonin. The findings indicate that the transcript levels of the LsGRAS13 gene were higher on days 6, 9, 15, 18, and 27 under the high-temperature (35/30 °C) treatment with melatonin than on the same treatment days without melatonin. The functional studies demonstrate that silencing LsGRAS13 accelerated bolting in lettuce. Furthermore, the paraffin sectioning results showed that flower bud differentiation in LsGRAS13-silenced plants occurred significantly faster than in control plants. In this study, the LsGRAS genes were annotated and analyzed, and the expression pattern of the LsGRAS gene following melatonin treatment under high-temperature conditions was explored. This exploration provides valuable information and identifies candidate genes associated with the response mechanism of lettuce plants high-temperature stress.

A variety of endogenous hormone signals, developmental cues, and environmental stressors can trigger and promote leaf lettuce bolting. One such factor is gibberellin (GA), which has linked to bolting. However, the signaling pathways and the mechanisms that regulate the process have not been discussed in full detail. To clarify the potential role of GAs in leaf lettuce, significant enrichment of GA pathway genes was found by RNA-seq, among which the LsRGL1 gene was considered significant. Upon overexpression of LsRGL1, a noticeable inhibition of leaf lettuce bolting was observed, whereas its knockdown by RNA interference led to an increase in bolting. In situ hybridization analysis indicated a significant accumulation of LsRGL1 in the stem tip cells of overexpressing plants. The leaf lettuce plants stably expressing LsRGL1 were examined concerning differentially expressed genes through RNA-seq analysis, and the data indicated an enhanced enrichment of these genes in “plant hormone signal transduction” and “phenylpropanoid biosynthesis” pathways. Additionally, significant changes in LsWRKY70 gene expression were identified in COG functional classification. The results of the yeast one-hybrid, GUS, and BLI experiments showed that LsRGL1 proteins directly bind to the LsWRKY70 promoters. Silencing LsWRKY70 by VIGS can delay bolting, regulate the expression of endogenous hormones, ABA-linked genes, and flowering genes, as well as improve the nutritional quality of leaf lettuce. These results strongly associate the positive regulation of bolting with LsWRKY70 by identifying its vital functions in the GA-mediated signaling pathway. The data obtained in this research is invaluable for further experiments concerning the development and growth of leaf lettuce.

Lettuce is one of the most popular leafy vegetables in the world, but it is prone to high-temperature stress in the cultivation process leading to bolting, which affects the yield. The plant-specific transcription factors, GRAS proteins, play an important role which regulates plant growth development and abiotic stress. However, there is no comprehensive study of the GRAS gene family in lettuce. In this study, the complete LsGRAS genome was identified its expression was analyzed. The results showed that the 59 LsGRAS genes were classified phylogenetically divided into 4 conserved subfamilies and distributed unevenly on 9 chromosomes, with 50% physically adjacent to at least one another and 100% localized on the nucleus. Chromosome localization and gene structure analysis suggested that duplication events and a large number presence of intronless genes might be the reason why the LsGRAS gene family expands massively. Combined with gene annotation and interaction network analysis, the expression pattern of the LsGRAS gene under high-temperature treatment was analyzed, revealing the potential different functions of the LsGRAS gene under high-temperature stress. In conclusion, this study provides valuable information and candidate genes for improving the ability of lettuce to tolerate high-temperature stress.

High temperature is one of the primary environmental stress factors affecting the bolting of leaf lettuce. To determine the potential role of melatonin in regulating high-temperature induced bolting in leaf lettuce (Lactuca sativa L.), we conducted melatonin treatment of the bolting-sensitive cultivar “S39.” The results showed that 100 μmol L⁻¹ melatonin treatment significantly promoted growth, and melatonin treatment delayed high-temperature-induced bolting in lettuce. RNA-seq analysis revealed that the differentially expressed genes (DEGs) involved in “plant hormone signal transduction” and “phenylpropanoid biosynthesis” were significantly enriched during high-temperature and melatonin treatment. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis suggested that the expression patterns of abscisic acid (ABA)-related genes positively correlated with stem length during leaf lettuce development. Furthermore, weighted gene co-expression network analysis (WGCNA) demonstrated that MYB15 may play an important role in melatonin-induced resistance to high temperatures. Silencing the LsMYB15 gene in leaf lettuce resulted in early bolting, and exogenous melatonin delayed early bolting in leaf lettuce at high temperatures. Our study provides valuable data for future studies of leaf lettuce quality.