How fall dormancy benefits alfalfa winter-survival? Physiologic and transcriptomic analyses of dormancy process

Zhi-Ying Liu,Zong-Li Wang,Xi-Liang Li,Taogetao Baoyin

doi:10.1186/s12870-019-1773-3

Abstract

BackgroundFall dormancy and freezing tolerance characterized as two important phenotypic traits, have great effects on productivity and persistence of alfalfa (Medicago sativa L.). Despite the fact that one of the most limiting traits for alfalfa freezing tolerance in winter is fall dormancy, the interplay between fall dormancy and cold acclimation processes of alfalfa remains largely unknown. We compared the plant regrowth, winter survival, raffinose and amino acids accumulation, and genome-wide differentially expressed genes of fall-dormant cultivar with non-dormant cultivar under cold acclimation.ResultsAveraged over both years, the non-dormant alfalfa exhibited largely rapid regrowth compared with fall dormant alfalfa after last cutting in autumn, but the winter survival rate of fall dormant alfalfa was about 34-fold higher than that of non-dormant alfalfa. The accumulation of raffinose and amino acids were significantly increased in fall dormant alfalfa, whereas were decreased in non-dormant alfalfa under cold acclimation. Expressions of candidate genes encoding raffinose biosynthesis genes were highly up-regulated in fall dormant alfalfa, but down-regulated in non-dormant alfalfa under cold acclimation. In fall dormant alfalfa, there was a significantly down-regulated expression of candidate genes encoding the glutamine synthase, which is indirectly involved in the proline metabolism. A total of eight significantly differentially expressed transcription factors (TFs) related to CBF and ABRE-BFs were identified. The most up-regulated TFs in fall dormant alfalfa cultivar were ABF4 and DREB1C.ConclusionsFall dormant alfalfa drastically increased raffinose and amino acids accumulation under cold acclimation. Raffinose-associated and amino acid-associated genes involved in metabolic pathways were more highly expressed in fall dormant alfalfa than non-dormant alfalfa under cold acclimation. This global survey of transcriptome profiles provides new insights into the interplay between fall dormancy and cold acclimation in alfalfa.

Highlights

Fall dormancy and freezing tolerance characterized as two important phenotypic traits, have great effects on productivity and persistence of alfalfa (Medicago sativa L.)
Plant growth and winter survival The NDT alfalfa exhibited the largely rapid regrowth condition compared with the fall dormant (FDT) in the field after last cutting (Fig. 1a)
There was a significant difference in natural plant height (NPH) between FDT and NDT alfalfa cultivars in two consecutive years

Summary

Introduction

Fall dormancy and freezing tolerance characterized as two important phenotypic traits, have great effects on productivity and persistence of alfalfa (Medicago sativa L.). Bud dormancy, a case of endodormancy, allows perennial plants of temperate and boreal zones to survive low winter temperatures. This dormancy has a negative impact on productivity of perennial herbaceous plants worldwide [5]. Raffinose (one of the RFOs) as a good indicator of freezing tolerance, has accumulated largely under cold stress in many plants, such as Ajuga reptans, which is a frost-hardy perennial labiate [3], Arabidopsis thaliana [29], vetch (Vicia villosa) [31], rice (Oryza sativa) [47] and cucumber (Cucumis sativus) [49]. The accumulation of amino acids is mainly induced by related enzyme in the amino acids metabolism pathway, which improves cold tolerance [11]

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