Defect in Brnym1, a magnesium-dechelatase protein, causes a stay-green phenotype in an EMS-mutagenized Chinese cabbage (Brassica campestris L. ssp. pekinensis) line

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 staygreen 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 magnesiumdechelatase. 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.

Revealing Distinctions in Genetic Diversity and Adaptive Evolution Between Two Varieties of Camellia sinensis by Whole-Genome Resequencing

“…Mutation sites in genic regions may have important effects on plant growth and development (Jin et al, 2016(Jin et al, , 2018Xanthopoulou et al, 2019;Wang et al, 2020). For example, a single nucleotide mutation in gibberellic acid receptor GID1 could cause a gibberellic acid-insensitive dwarf phenotype in peaches (Cheng et al, 2019).…”

The novel gene BrMYB2, located on chromosome A07, with a short intron 1 controls the purple-head trait of Chinese cabbage (Brassica rapa L.)

“…For example, mutation of a single proline to leucine substitution in BnRGA led to a semidwarf mutant phenotype of B. napus 44 . A nonsynonymous SNP in the third exon of Brnym1 produced an amino acid substitution in the highly conserved domain of magnesium dechelatase, which generated a stay-green phenotype of Chinese cabbage 45 . Similarly, variations in amino acids caused by SNPs in Bror did not affect its gene function, whereas an insertion in Bror caused early termination of translation and loss of gene function in orange head Chinese cabbage 46 .…”

SlRCM1, which encodes tomato Lutescent1, is required for chlorophyll synthesis and chloroplast development in fruits

“…SGR1 , encoding Mg dechelatase, promotes chloroplast degradation during plant maturation 20 . Mutation of SGR1 in Chinese cabbage leads to increased chlorophyll concentrations and a stay-green phenotype 21 . In Arabidopsis , the bcm1 mutant exhibits a pale-green leaf phenotype due to reduced chlorophyll contents.…”