Integrated transcriptomic and endogenous hormones analyses revealed the molecular mechanism of light and auxin for the regeneration of callus tissue in seashore paspalum

Abstract

Background: Seashore paspalum (Paspalum vaginatum O. Swartz) is a halophyte known for its exceptional salt tolerance and ecological adaptability. It is an excellent candidate for studying salt tolerance mechanisms and screening salt tolerance genes. However, the difficulties with callus tissue regeneration and the influence of genotype during cultivation provide a significant obstacle to the process of molecular breeding employing genetic transformation and gene editing techniques in seashore paspalum. Results: To elucidate the molecular mechanism of callus regeneration in seashore paspalum, this study analyzed the content of endogenous hormones and investigated the effects of light, KT, and genotype on callus regeneration; Through transcriptome analysis between different treatments, the molecular mechanisms were explored. Under light conditions, almost all callus tissues of genotype I could produce regenerated green buds, but genotype II could not regenerate. A total of 106.2 Gb clean readings were obtained from 12 cDNA sample libraries in four regeneration states (CK, KT-D, KT-L, and KT-L-NR). The Pearson correlation coefficients, principal component analysis, and DEG hierarchical clustering heatmap analysis results indicated good intra-group repeatability and reliable data. The specific expression genes induced by different genotypes (KT-L-NR vs KT-L) (3083) were significantly higher than those in other groups by Venn plot analysis. A total of 73 endogenous hormone substances were quantitatively detected in all samples. KEGG enrichment analysis showed that all comparison groups significantly enriched differentially changed hormones (DCHs) in diterpenoid biosynthesis and plant hormone signal transduction pathways. In KT-L, GA₅ and GA₅₁ were significantly higher than those in other groups, while GA₂₀ and GA₂₉ were significantly lower. KT-L-NR showed noticeably higher levels of GA₃, GA₂₀, and GA₂₉, which could be a contributing cause to the incapacity of callus regeneration. The expression level of GA2ox (Pavag03G280900. v3.1) was very high, significantly negatively regulating GA₅₁. In KT-L, the content of ABA and JA were the lowest and significantly lower than that in KT-L-NR. The content of indole-3-acetic acid (IAA) in KT-L and KT-L-NR were significantly higher than that in CK and KT-D, indicating that light played an important role in synthesizing of IAA, which was beneficial for the regeneration of callus tissue. Conclusions: This is the first report on callus regeneration mechanisms of seashore paspalum by combined transcriptome and endogenous hormone profiling. The results will improve the understanding of molecular mechanisms and the effects of endogenous hormones, and provide new insights to address the issue of genotype dependence in callus regeneration.