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

Abstract

Background Fall 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. Results Averaged 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. Conclusions Fall 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. Electronic supplementary material The online version of this article (10.1186/s12870-019-1773-3) contains supplementary material, which is available to authorized users.

Different Genes Express Analysis of root crown of alfalfa under low temperature stress

“…In addition, many studies have reported that the WRKY family is involved in the low temperature stress response. For example, up-regulation of transcription factor expression in most WRKY gene families (WRKY 30,33,41,46,48,51,53,65,70) in Hevea brasiliensis under low temperature stress (24 h cold treatment at 4 °C) [67]. In particular, the WRKY65 gene expression in cassava was up-regulation under low temperature stress [68], consistent with the results of our study.…”

“…Therefore, the ability for regrowth in the spring reflects the cold resistance of the forages in the field [48]. A recent study have shown that different varieties of alfalfa have significant differences in winter cold resistance, mainly in dormancy and winter survival rate [41]. In this study, the winter survival rate of Longmu 806 variety (98.09%) was significantly higher than that of Sardi variety (26.69%, P<0.05, Fig.…”

“…To our knowledge, some previous study have reported that transcriptome sequencing technology was used to analyze differentially expressed genes related to alfalfa leaves, taproots, and crown buds [41,42,49]. However, unlike previous studies, in order to understand the comprehensive genetic regulation mechanism of alfalfa low temperature resistance, this study focused on the expression patterns of low temperature response genes in the root crown of alfalfa, and explored the mechanism of winter hardiness response of different alfalfa roots during wintering.…”

“…In addition, studies on differentially expressed genes of low temperature resistance of alfalfa varieties have also been reported. A recent study reported that transcriptome high-throughput sequencing technology has been used to analysis the expression of the gene of the seedling [10], taproots [41], and crown buds [42] of alfalfa, which provides valuable resources for functional genomics research on plant cold tolerance in the future. However, the understanding of genetic response information for low temperature stress was limited, since some of the previous studies only RNA-seq the seedling, taproots, and crown buds of alfalfa.…”

Differential expression analysis of genes in the root crown of alfalfa under low-temperature stress

“…For example, with the introduction of a new generation of RNA-Seq, transcriptome sequencing technology has been used to identify lowtemperature stress response genes in Ipomoea batatas [33], Populus tomentosa [34], Capsicum annuum [35], and Magnolia wufengensis [36]. Moreover, some recent studies have reported that the use of transcriptome sequencing technology to analyze the expression of genes in the seedlings [7], taproots [37], and crown buds [38] of alfalfa, which provides valuable resources for functional genomics research on alfalfa cold tolerance. However, the understanding of genetic regulation information regarding low-temperature stress remains limited.…”