Identification and characterization of regulatory pathways involved in early flowering in the new leaves of alfalfa (Medicago sativa L.) by transcriptome analysis

Dongmei Ma,Peisheng Mao,Xiaohui Cao,Bei Liu,Lingqiao Ge,Fang Liu,Xiqing Ma,Yinyin Weng

doi:10.1186/s12870-020-02775-9

Abstract

BackgroundAlfalfa (Medicago sativa L.) is a perennial legume extensively planted throughout the world as a high nutritive value livestock forage. Flowering time is an important agronomic trait that contributes to the production of alfalfa hay and seeds. However, the underlying molecular mechanisms of flowering time regulation in alfalfa are not well understood.ResultsIn this study, an early-flowering alfalfa genotype 80 and a late-flowering alfalfa genotype 195 were characterized for the flowering phenotype. Our analysis revealed that the lower jasmonate (JA) content in new leaves and the downregulation of JA biosynthetic genes (i.e. lipoxygenase, the 12-oxophytodienoate reductase-like protein, and salicylic acid carboxyl methyltransferase) may play essential roles in the early-flowering phenotype of genotype 80. Further research indicated that genes encode pathogenesis-related proteins [e.g. leucine rich repeat (LRR) family proteins, receptor-like proteins, and toll-interleukin-like receptor (TIR)-nucleotide-binding site (NBS)-LRR class proteins] and members of the signaling receptor kinase family [LRR proteins, kinases domain of unknown function 26 (DUF26) and wheat leucine-rich repeat receptor-like kinase10 (LRK10)-like kinases] are related to early flowering in alfalfa. Additionally, those involved in secondary metabolism (2-oxoglutarate/Fe (II)-dependent dioxygenases and UDP-glycosyltransferase) and the proteasome degradation pathway [really interesting new gene (RING)/U-box superfamily proteins and F-box family proteins] are also related to early flowering in alfalfa.ConclusionsIntegrated phenotypical, physiological, and transcriptomic analyses demonstrate that hormone biosynthesis and signaling pathways, pathogenesis-related genes, signaling receptor kinase family genes, secondary metabolism genes, and proteasome degradation pathway genes are responsible for the early flowering phenotype in alfalfa. This will provide new insights into future studies of flowering time in alfalfa and inform genetic improvement strategies for optimizing this important trait.

Highlights

Alfalfa (Medicago sativa L.) is a perennial legume extensively planted throughout the world as a high nutritive value livestock forage
Past endeavors of flowering time studies discovered six major regulatory pathways in model plants Arabidopsis, rice (Oryza.sativa L.), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.) [5, 6]. These pathways can be categorized into two groups: the photoperiod, vernalization, and ambient pathways that respond to environmental conditions, and the autonomous, gibberellin, and age pathways that respond to endogenous cues associated with the up/downregulation of floral integrator genes, including FLOWERING LOCUS T (FT), FLOWERING LOCUS C (FLC), CONSTANS (CO) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) [7,8,9]
We identified 2148 (1454 upregulated/694 downregulated) and 1972 (1142 upregulated/ 830 downregulated) differentially expressed genes (DEGs) between new leaves (NL) and mature leaves (ML) in 195 and genotype 80 respectively, among which 942 and 766 DEGs were exclusively expressed in genotype 195 and 80, respectively (Fig. 3a and b; Additional file 1: Table S1)

Summary

Introduction

Alfalfa (Medicago sativa L.) is a perennial legume extensively planted throughout the world as a high nutritive value livestock forage. Past endeavors of flowering time studies discovered six major regulatory pathways in model plants Arabidopsis, rice (Oryza.sativa L.), wheat (Triticum aestivum L.), and barley (Hordeum vulgare L.) [5, 6]. PUB13, a U-box protein possessing E3 ubiquitin ligase, physically interacts with HFR1 (long hypocotyl in far-red light1) to regulate photomorphogenesis and flowering time in Arabidopsis [20]. Whether their alfalfa homologs participate in flowering time regulation is not clear

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