## 4 Discussion
The results from the differential expression analysis showed that the expression patterns observed in both the overall heatmap and the individual heatmaps demonstrate that the seed maturity stage plays a significant role in influencing gene expression. GO enrichment analysis highlighted that the S1-S3 comparison exhibited, in most cases, the greatest number of upregulated and downregulated genes in GO terms associated with phosphorus metabolic processes. More precisely, this is confirmed in annotations like \"phosphorus metabolic process\" (GO:0006793) and \"phosphate-containing compound metabolic process\" (GO:0006796) in all three P treatments. An additional noteworthy observation from the GO analysis, particularly within the annotations related to the \"phosphorus metabolic process\", is that the majority of enriched DEGs were found to be in a downregulated state. Functional analysis of the DEGs by GO analysis revealed that the majority of DEGs related to P metabolic processes mainly consist of downregulated genes in all three P treatments. The influence of P in the downregulated DEGs was observed in the annotations \"phosphorus metabolic process\", \"phosphate-containing compound metabolic process\" and \"phosphorylation\" as the total number of downregulated DEGs decreased while the level of P fertilization increased. According to studies, lentils', faba beans' and peas' increased yield has been ascribed to higher P fertilization [54]. On the other hand, P deficiency induces the increase in certain phenolic substances in all the vegetative parts of the lentil plants [21]. Lentil, like other legumes, has a high demand for P for both seed quality and plant growth [43], and unpublished data from our team certainly confirms this statement. Through KEGG pathway analysis it was observed that among the upregulated DEGs, the following pathways exhibited the highest number of enriched DEGs: the spliceosome pathway for the P0 treatment, the protein processing in the endoplasmic reticulum pathway for the P1 treatment, and the ribosome pathway for the P2 treatment. In the case of downregulated DEGs, it was consistently observed that the ribosome pathway had the highest number of DEGs across all treatments. RNA sequencing results were investigated further to reveal how the P treatment and the seed maturity stage inside the pod influence the expression levels of specific genes in the phenylpropanoid pathway. The selected genes seem to be highly expressed in S1, slightly less expressed in S2 and even less expressed in S3. This indicates that the gene expression decreases as the seed matures, while the expression levels remain unaffected by P treatments. The developmental stage appears to be a crucial factor affecting the gene expression at pivotal points within the pathway. A specific step in the phenylpropanol pathway is blocked in low-tannin lentils at the stage of formation of anthocyanins and proanthocyanidins from dihydromyrecitin, whereas a slighter blockage in this step has been found in gray genotypes. Additionally, in low-tannin seeds a lack of dihydroflavonols is observed, which are precursors for anthocyanin and proanthocyanidin generation [55]. The FLS and F3H genes' expression, though, does not follow the same pattern as the rest of the studied genes of the phenylpropanol pathway. The expression levels of the FLS gene appear to decrease as the P level increases. The F3H expression seems to be influenced by the P level when considering each seed maturity stage separately. The pattern of the P influence, though, is not consistent among the P treatments, which may suggest the existence of additional factors regulating the expression of F3H. [PERSON] et al. reported that two genes in the FLS family, FLS1 and FLS2, are highly expressed in the early stages of seed development, while another gene in the FLS family, FLS3, is highly expressed in the later stages of seed development, suggesting that the FLS genes may play different roles in regulating seed development [30]. In the study conducted by [PERSON] et al.