A base mutation of MiSGR2 alters peel color formation in Mangifera indica L.

Fruit color is an important breeding trait of mango (Mangifera indica L.), that directly affects it's appearance quality and commodity value. The mango cultivars, 'Jinhuang' ('JH') and 'Guifei' ('GF'), exhibit a peel color transition from green to yellow or red during ripening. In contrast, the cultivar 'Guiqi' ('GQ') retains its green peel and sweet fragrance even at full ripeness, exhibiting a stay-green phenotype. Here, we identified two Mangifera indica Stay-Green genes (MiSGR1 and MiSGR2) from these cultivars and investigate their roles in peel color development. The expression level of MiSGR1 was markedly lower in 'GQ' than in 'JH' and 'GF', whereas MiSGR2 showed no significant expression difference. Sequencing analysis identified a single-base substitution (G→A) at position 641 in the open reading frame of MiSGR2 from 'GQ', which introduced a premature stop codon (designated MiSGR2^STOP) and truncated 43 amino acids relative to MiSGR2 from 'GF' and 'JH'. Over-expression assay in heterologous system demonstrated that both MiSGR1 and MiSGR2 catalyzed chlorophyll degradation, whereas MiSGR2^STOP lacked this activity. Yeast two-hybrid and BiFC analyses further confirmed that MiSGR1 and MiSGR2 interacted with protein MiPPH1, while MiSGR2^STOP failed to do so. These results suggest that the single-nucleotide mutation in MiSGR2 disrupts its activity in chlorophyll degradation and interaction with MiPPH1, leading to the stay-green phenotype of 'GQ'. Our findings provide new insight into the molecular regulation of peel color in mango and a genetic basis for breeding cultivars with improved visual and nutritional quality.