Abstract
Key messageA dwarfism gene LacDWARF1 was mapped by combined BSA-Seq and comparative genomics analyses to a 65.4 kb physical genomic region on chromosome 05.Dwarf architecture is one of the most important traits utilized in Cucurbitaceae breeding because it saves labor and increases the harvest index. To our knowledge, there has been no prior research about dwarfism in the sponge gourd. This study reports the first dwarf mutant WJ209 with a decrease in cell size and internodes. A genetic analysis revealed that the mutant phenotype was controlled by a single recessive gene, which is designated Lacdwarf1 (Lacd1). Combined with bulked segregate analysis and next-generation sequencing, we quickly mapped a 65.4 kb region on chromosome 5 using F2 segregation population with InDel and SNP polymorphism markers. Gene annotation revealed that Lac05g019500 encodes a gibberellin 3β-hydroxylase (GA3ox) that functions as the most likely candidate gene for Lacd1. DNA sequence analysis showed that there is an approximately 4 kb insertion in the first intron of Lac05g019500 in WJ209. Lac05g019500 is transcribed incorrectly in the dwarf mutant owing to the presence of the insertion. Moreover, the bioactive GAs decreased significantly in WJ209, and the dwarf phenotype could be restored by exogenous GA3 treatment, indicating that WJ209 is a GA-deficient mutant. All these results support the conclusion that Lac05g019500 is the Lacd1 gene. In addition, RNA-Seq revealed that many genes, including those related to plant hormones, cellular process, cell wall, membrane and response to stress, were significantly altered in WJ209 compared with the wild type. This study will aid in the use of molecular marker-assisted breeding in the dwarf sponge gourd.
Highlights
The sponge gourd (2n = 26) is an important vegetable and medicinal plant in tropical and subtropical regions, and has a long history of cultivation in Asian and African tropical countries (Kalloo 1993; Wu et al 2014, 2016)
An insertion of approximately 4 kb was found in the first intron of mutant allele. This insertion caused the incorrect transcription of Lac05g019500, resulting reduction in the amount of bioactive GAs in WJ209. The dwarf mutant (WJ209), which is responsible for the dwarfism phenotype in sponge gourd
The dwarf mutant WJ209 was much shorter than the wild type (WT) (Fig. 1a)
Summary
The semi-dwarf variety of rice (Sasaki et al 2002; Suh 1978), increases the yield potential and nitrogen responsiveness, resulting in an increase in the harvest index of more than 60% (Khush 2001; Peng et al 1999), which constitutes an important breakthrough in the history of crop improvement.
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