Identification and function analysis of yellow-leaf mutant (YX-yl) of broomcorn millet

Abstract

Background Broomcorn millet is highly tolerant to drought and barren soil. Changes in chlorophyll content directly affect leaf color, which subsequently leadsleading to poor photosynthetic performance and reduced crop yield. Herein, we isolated a yellow leaf mutant (YX-yl) using a forward genetics approach and evaluated its agronomic traits, photosynthetic pigment content, chloroplast ultrastructure, and chlorophyll precursors. Furthermore, the molecular mechanism of yellowing was explored using transcriptome sequencing. Results The YX-yl mutant showed significantly decreased plant height and low yield. The leaves exhibited a yellow-green phenotype and poor photosynthetic capacity during the entire growth period. The content of chlorophyll a, chlorophyll b, and carotenoids in YX-yl leaves was lower than that in wild-type leaves. Chlorophyll precursor analysis results showed that chlorophyll biosynthesis in YX-yl was hindered by the conversion of porphobilinogen to protoporphyrin IX. Examination of chloroplast ultrastructure in the leaves revealed that the chloroplasts of YX-yl accumulated on one side of the cell. Moreover, the chloroplast structure of YX-yl was degraded. The inner and outer membranes of the chloroplasts could not be distinguished well. The numbers of grana and grana thylakoids in the chloroplasts were low. The transcriptome of the yellowing mutant YX-yl was sequenced and compared with that of the wild type. Nine chlorophyll-related genes with significantly different expression profiles were identified: PmUROD, PmCPO, PmGSAM, PmPBDG, PmLHCP, PmCAO, PmVDE, PmGluTR, and PmPNPT. The proteins encoded by these genes were located in the chloroplast, chloroplast membrane, chloroplast thylakoid membrane, and chloroplast matrix and were mainly involved in chlorophyll biosynthesis and redox-related enzyme regulation. Conclusions YX-yl is an ideal material for studying pigment metabolism mechanisms. Changes in the expression patterns of some genes between YX-yl and the wild type led to differences in chloroplast structures and enzyme activities in the chlorophyll biosynthesis pathway, ultimately resulting in a yellowing phenotype in the YX-yl mutant. Our findings provide an insight to the molecular mechanisms of leaf color formation and chloroplast development in broomcorn millet.

Physiological and transcriptomic analysis of a yellow leaf mutant in watermelon

“…The same results have been reported for other crops 11 – 15 . The decreased pigments in Yl2 probably affects the chloroplast development and photosynthesis process 11 , 14 , 15 .…”

“…The chloroplasts in many leaf color mutants, such as cucumber and rice were also imperfect, and contained looser thylakoids than those in the WT 11 – 16 . In the yellow‒leaf mutant ( YX-yl ) of broomcorn millet, chloroplast development was inhibited owing to degeneration of the chloroplast ultrastructure, which exhibited fewer grana thylakoids and almost no stroma thylakoids 14 . A green‒yellow leaf wucai ( Brassica campestris L.) mutant exhibited fewer chloroplasts per cell and looser stromal lamellae 15 .…”

“…The lower chlorophyll pigment content, combined with damaged chloroplasts, might account for the poorer photosynthetic performance and light transfer efficiency in the leaf color mutant 14 . In previous studies, lower chlorophyll content was found to be closely related to the photosynthetic rate and light-use efficiency.…”

A highly conserved amino acid mutation in TaCHLI-7D affects leaf color and yield-related traits in wheat

“…In higher plants, chloroplast formation and development is a complicated process that demands a highly coordinated and nely-tuned interplay between gene transcription, translation, protein renewal, and metabolism, whereas defects in any one of these steps can cause chloroplast impairment and leaf pigmentation Albrecht, 2011, Zhang et al, 2020). Several studies have investigated chlorophyll biosynthesis mechanisms by examining mutants with altered leaf coloration (Wang et al, 2022. Such mutants frequently exhibit reduced photosynthetic activity due to a lack of photosynthetic components or altered development due to the accumulation of other pigments (Liu et al, 2016, Ding et al, 2019.…”

“…Such mutants frequently exhibit reduced photosynthetic activity due to a lack of photosynthetic components or altered development due to the accumulation of other pigments (Liu et al, 2016, Ding et al, 2019. These mutants provide valuable tools for studying plant photosynthesis (Wang et al, 2022), photomorphogenesis (Matsumoto et al, 2004), and disease resistance (Shah and Paulsen, 2003a).…”