Multi-omics analyses reveal new insights into nutritional quality changes of alfalfa leaves during the flowering period

Yinghao Liu; Wenqiang Fan; Qiming Cheng; Lianyi Zhang; Ting Cai; Quan Shi; Zuo Wang; Chun Chang; Qiang Yin; Xiaowei Jiang; Ke Jin

doi:10.3389/fpls.2022.995031

Multi-omics analyses reveal new insights into nutritional quality changes of alfalfa leaves during the flowering period

Front Plant Sci. 2022 Nov 30:13:995031. doi: 10.3389/fpls.2022.995031. eCollection 2022.

Authors

Yinghao Liu¹, Wenqiang Fan², Qiming Cheng³, Lianyi Zhang⁴, Ting Cai⁴, Quan Shi⁴, Zuo Wang⁴, Chun Chang¹, Qiang Yin¹, Xiaowei Jiang¹, Ke Jin¹

Affiliations

¹ Key Laboratory of Forage Cultivation, Processing and High Efficient Utilization of Ministry of Agriculture and Rural Affairs, Institute of Grassland Research of Chinese Academy of Agricultural Sciences, Hohhot, China.
² Key Laboratory of Grassland Resources, Ministry of Education, Inner Mongolia Agricultural University, Hohhot, China.
³ College of Animal Science, Guizhou University, Guiyang, China.
⁴ Key Laboratory of Efficient Utilization of Forage, Inner Mongolia Agricultural and Animal Husbandry Technology Extension Center, Hohhot, China.

Abstract

High-quality alfalfa is an indispensable resource for animal husbandry and sustainable development. Its nutritional quality changes dramatically during its life cycle and, at present, no molecular mechanisms for nutrient metabolic variation in alfalfa leaves at different growth stages have been clearly reported. We have used correlation and network analyses of the alfalfa leaf metabolome, proteome, and transcriptome to explore chlorophyll, flavonoid, and amino acid content at two development stages: budding stage (BS) and full-bloom stage (FBS). A high correlation between the expression of biosynthetic genes and their metabolites revealed significant reductions in metabolite content as the plant matured from BS to FBS. l-Glutamate, the first molecule of chlorophyll biosynthesis, decreased, and the expression of HemA, which controls the transformation of glutamyl-tRNA to glutamate 1-semialdehyde, was down-regulated, leading to a reduction in leaf chlorophyll content. Flavonoids also decreased, driven at least in part by increased expression of the gene encoding CYP75B1: flavonoid 3'-monooxygenase, which catalyzes the hydroxylation of dihydroflavonols and flavonols, resulting in degradation of flavonoids. Expression of NITRILASE 2 (NIT2) and Methyltransferase B (metB), which regulate amino acid metabolism and influence the expression of genes of the glycolysis-TCA pathway, were down-regulated, causing amino acid content in alfalfa leaves to decrease at FBS. This study provides new insights into the complex regulatory network governing the content and decrease of chlorophyll, amino acids, flavonoids, and other nutrients in alfalfa leaves during maturation. These results further provide a theoretical basis for the generation of alfalfa varieties exhibiting higher nutritional quality, high-yield cultivation, and a timely harvest.

Keywords: alfalfa leaves; amino acids; chlorophyll; flavonoids; metabolomics; proteomics; transcriptomics.