GmENDO-like 1, a structurally divergent homolog of S1/P1-type endonuclease, modulates the vegetative-to-reproductive...

GmENDO-like 1, a structurally divergent S1/P1 endonuclease homolog, modulates soybean vegetative-to-reproductive transition; its knockout delays flowering and accelerates leaf senescence. Soybean is a monocarpic crop in which the transition from vegetative to reproductive growth triggers the onset of senescence in vegetative tissues. In this study, we identified a soybean homolog of the S1/P1-type endonuclease gene, GmENDO-like 1, which was significantly upregulated during leaf senescence. Sequence analysis revealed that GmENDO-like 1 has substantial deletions at both the N- and C-termini, resulting in the loss of key residues essential for the active center of canonical S1/P1-type nucleases. Specifically, among the nine conserved amino acids responsible for metal ion coordination, one tryptophan (Trp), two histidines (His), and one aspartic acid (Asp) residue are absent. Although these deletions result in a significant rearrangement of the trinuclear metal-binding center, GmENDO-like 1 remarkably retains intrinsic catalytic activity. Using CRISPR/Cas9-mediated genome editing, we generated two knockout mutant lines of the GmENDO-like 1 gene. Phenotypic analysis revealed a markedly delayed flowering time and an obviously precocious leaf senescence in the GmENDO-like 1 mutant plants. These observations were further corroborated by the altered expression levels of flowering- and senescence-associated marker genes. Both the 100-seed weight and per-plant yield of the mutants were significantly decreased. Collectively, these findings establish GmENDO-like 1 as a functional, evolutionarily divergent nuclease and an essential modulator regulating the vegetative-to-reproductive phase transition in soybean.