Physiological and transcriptomic analysis of a yellow leaf mutant in watermelon

Abstract

Leaf color mutants are important materials for studying chloroplast and photomorphogenesis, and can function as basic germplasms for genetic breeding. In an ethylmethanesulfonate mutagenesis population of watermelon cultivar “703”, a chlorophyll-deficient mutant with yellow leaf (Yl2) color was identified. The contents of chlorophyll a, chlorophyll b, and carotenoids in Yl2 leaves were lower than those in wild-type (WT) leaves. The chloroplast ultrastructure in the leaves revealed that the chloroplasts in Yl2 were degraded. The numbers of chloroplasts and thylakoids in the Yl2 mutant were lower, resulting in lower photosynthetic parameters. Transcriptomic analysis identified 1292 differentially expressed genes, including1002 upregulated and 290 downregulated genes. The genes involved in chlorophyll biosynthesis (HEMA, HEMD, CHL1, CHLM, and CAO) were significantly downregulated in the Yl2 mutant, which may explain why chlorophyll pigment content was lower than that in the WT. Chlorophyll metabolism genes such as PDS, ZDS and VDE, were upregulated, which form the xanthophyll cycle and may protect the yellow‒leaves plants from photodamage. Taken together, our findings provide insight into the molecular mechanisms of leading to leaf color formation and chloroplast development in watermelon.

Effects of different light intensity on leaf color changes in a Chinese cabbage yellow cotyledon mutant

“…As expected, our studies also showed the changes in chlorophyll and carotenoid contents in Chinese cabbage yellow cotyledon mutant 19YC-2. The significantly higher carotenoid content and lower chlorophyll content were found in the cotyledons of 19YC-2, which may be responsible for the yellow cotyledon phenotypes and was similar to the previous reports ( Zhang et al., 2015 ; Sun et al., 2022 ; Xu et al., 2023 ). It is known that chloroplast development also affects the accumulation of chlorophyll and carotenoid and leaf color changes ( Pogson and Albrecht, 2011 ; Zhao et al., 2020 ).…”

“…The yellow-green leaf color in wheat ( Triticum aestivum L. ) was consequence of the decreased chlorophyll content and abnormal chloroplast development ( Wu et al., 2018 ). In addition, chlorophyll deficient was also showed to cause yellow leaf phenotypes in watermelon ( Xu et al., 2023 ), and the chlorophyll deficient mutant in Pak-choi exhibited the obvious yellow leaves and the reduced total chlorophyll content ( Zhang et al., 2017 ). As expected, our studies also showed the changes in chlorophyll and carotenoid contents in Chinese cabbage yellow cotyledon mutant 19YC-2.…”

“…Leaf color mutants are widespread in plants, and one of the widely available mutation types is leaf yellowing. Numerous yellow leaf mutants have been identified and reported in many vegetable crops, such as pepper ( Yang et al., 2023 ), watermelon ( Xu et al., 2023 ), cucumber ( Zhang et al., 2022a ), wucai ( Nie et al., 2021 ), and Chinese cabbage ( Zhang et al., 2017 ; Zhao et al., 2021 ). Studies have demonstrated that yellow leaf phenotype of mutant is usually caused by the disrupted biosynthesis and degradation of chlorophyll and carotenoid ( Zhao et al., 2020 ), and thus it is commonly used for studying the photosynthetic system, pigment biosynthetic pathway, and genetic regulatory mechanism.…”

Molecular Mechanisms of Chlorophyll Deficiency in Ilex × attenuata ‘Sunny Foster’ Mutant

“…This process occurs on the thylakoid membranes of chloroplasts, which are structured into regularly stacked grana in higher plants, optimizing light harvesting and energy conversion efficiency [56]. Therefore, leaf color mutants often exhibit structural alterations in thylakoid organization, such as reduced grana stacks and irregular arrangement, indicating an underdeveloped chloroplast ultrastructure and potential loss of photosynthetic capacity [26,57]. For instance, in the pgb tea Chl-deficient mutant, mature leaves exhibited significantly fewer chloroplasts with defective morphology, lacking stacked thylakoid structures but containing numerous giant plastoglobuli, along with reduced osmiophilic granules and absence of starch granules in the plastids [58].…”

“…In recent years, researchers have employed various innovative techniques, such as transcriptomics, proteomics, metabolomics, and integrated approaches, to unravel the complex mechanisms behind leaf color mutation [26,27]. For instance, physiological and transcriptome analysis of I.…”