Abstract
Leaf color is an important target trait in Chinese cabbage breeding programs. Leaf yellowing may reduce crop commercial and nutritional values. Some plants with the “stay-green” trait maintain leaf greenness during senescence and even after death. Stay-green Chinese cabbage may be a focal point of future breeding projects because it could improve crop quality and yield and prolong shelf life. A new stay-green mutant, non-yellowing mutant 1 (nym1), was identified in Chinese cabbage derived from an ethyl methane sulfonate (EMS)-mutagenized population. The mutant had stay-green characteristics and a higher chlorophyll content than the wild-type during leaf senescence. The stay-green trait in the mutant Chinese cabbage was controlled by the recessive gene Brnym1. MutMap and KASP analyses showed that Brnym1 (BraA03g050600.3C) encodes an mg-dechelatase (SGR protein), which might be the causal gene of the mutation in Chinese cabbage. A nonsynonymous single nucleotide base substitution (G to A) in the third exon of Brnym1 caused an amino acid substitution from L to F in the highly conserved domain of the magnesium-dechelatase. Ectopic overexpression showed that the BrNYM1 gene of wild-type Chinese cabbage complemented the SGR-defective stay-green mutant nye1-1 of Arabidopsis. The magnesium-dechelatase activity in the nym1 mutant was significantly downregulated compared to that in the wild type. Brnym1 was relatively upregulated in the mutant during late senescence, and BrNYM1 was localized to the chloroplasts. These results indicate that Brnym1 (BraA03g050600.3C) is the causal gene of the stay-green mutation and could be of particular significance in the genetic improvement of Chinese cabbage.
Highlights
The stay-green trait generally refers to plants that retain their leaf greenness during senescence and even after death[1]
We discovered by MutMap and KASP that the mutation responsible for delayed degreening might be a nonsynonymous base pair change in Brnym[1]
Compared to “FT”, the mutant had leaves that did not turn yellow during senescence or after death at the cotyledon and rosette stages, respectively (Fig. 1a, b)
Summary
The stay-green trait generally refers to plants that retain their leaf greenness during senescence and even after death[1]. Stay-green mutants were classified into five types by Thomas and Howarth[2]. In type A plants, the onset of senescence is delayed, but its progression is normal. In type B plants, the timing of the onset of senescence is normal, but its progression is delayed. In type C plants, the plants are defective in terms of chlorophyll degradation.
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