Quantitative Trait Loci for Seed Size Variation in Cucurbits – A Review

Abstract

Cucurbits (Cucurbitaceae family) include many economically important fruit vegetable crops such as watermelon, pumpkin/squash, cucumber, and melon. Seed size (SS) is an important trait in cucurbits breeding, which is controlled by quantitative trait loci (QTL). Recent advances have deciphered several signaling pathways underlying seed size variation in model plants such as Arabidopsis and rice, but little is known on the genetic basis of SS variation in cucurbits. Here we conducted literature review on seed size QTL identified in watermelon, pumpkin/squash, cucumber and melon, and inferred 14, 9 and 13 consensus SS QTL based on their physical positions in respective draft genomes. Among them, four from watermelon (ClSS2.2, ClSS6.1, ClSS6.2, and ClSS8.2), two from cucumber (CsSS4.1 and CsSS5.1), and one from melon (CmSS11.1) were majoreffect, stable QTL for seed size and weight. Whole genome sequence alignment revealed that these major-effect QTL were located in syntenic regions across different genomes suggesting possible structural and functional conservation of some important genes for seed size control in cucurbit crops. Annotation of genes in the four watermelon consensus SS QTL regions identified genes that are known to play important roles in seed size control including members of the zinc finger protein and the E3 ubiquitinprotein ligase families. The present work highlights the utility of comparative analysis in understanding the genetic basis of seed size variation, which may help future mapping and cloning of seed size QTL in cucurbits.

Localization of quantitative trait loci for cucumber fruit shape by a population of chromosome segment substitution lines

“…S4; Table 1; Supplementary Table S2). More recently, two consensus QTLs (CsSS2.1 and CsSS2.2) associated with seed size have been reported on chromosome 2 in a review paper by Guo et al 56 , and CsSS2.1 displays overlapping, but larger than the identified QTLs for SDL and SW in the present study. The smaller QTL regions in this study will facilitate the future fine-mapping for genes responsible for seed size.…”

QTL Mapping of Fruit and Seed-related Traits in Watermelon Using Genotyping-by-Sequencing-based High-density Linkage Mapping

“…S6). Guo et al (2020) reviewed the genetic architecture of seed size variation in watermelon, and inferred 14 consensus QTL on seed size and which are distributed on 7 of the 11 watermelon chromosomes [1,17,[52][53][54][55]. Among them, qsl5.1, qsl5.2, qsl7.1, qsw3.1, qsw10.1, q20swt10.1 were not identi ed in previous studies.…”

Genetic Mapping and Identification of the Candidate Gene for White Seed Coat in Cucurbita maxima

“…Compare with dark-colored seed coat, light-colored seed is a desirable trait with great potential for improving seed quality [ 8 , 9 ]. In the edible seed genetic breeding, the varieties displaying white and thin seed coat are preferred for removing the seed coat conveniently and display a high kernel yield [ 10 ].…”

“…The seed coat displayed a wide range of colors such as brown, yellow, ivory, and white in Cucurbita species [ 10 , 11 ]. Seed coat color has been extensively studied in Arabidopsis and several oil crops such as Brassica napus , Glycine max , and some species in Cucurbitaceae [ 12 ].…”

“…In Cucurbitaceae species, compared to melon and cucumber, watermelon and pumpkin/squash display rich diversity on seed traits including seed size, seed weight, and seed colors, which seem to depend on the intended uses and under a significant artificial selection in modern breeding [ 10 ]. At present, genetic analysis and QTL localization of seed coat color has been studies in Cucurbitaceae crops such as melon and watermelon.…”