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. 2020 Nov 16;20(1):520.
doi: 10.1186/s12870-020-02695-8.

Natural variation of physiological traits, molecular markers, and chlorophyll catabolic genes associated with heat tolerance in perennial ryegrass accessions

Jing Zhang  1 , Hui Li  1 , Yiwei Jiang  2 , Huibin Li  3 , Zhipeng Zhang  4 , Zhipeng Xu  1 , Bin Xu  5 , Bingru Huang  6
Affiliations

Natural variation of physiological traits, molecular markers, and chlorophyll catabolic genes associated with heat tolerance in perennial ryegrass accessions

Jing Zhang et al. BMC Plant Biol. .

Abstract

Background: Identification of genetic diversity in heat tolerance and associated traits is of great importance for improving heat tolerance in cool-season grass species. The objectives of this study were to determine genetic variations in heat tolerance associated with phenotypic and physiological traits and to identify molecular markers associated with heat tolerance in a diverse collection of perennial ryegrass (Lolium perenne L.).

Results: Plants of 98 accessions were subjected to heat stress (35/30 °C, day/night) or optimal growth temperature (25/20 °C) for 24 d in growth chambers. Overall heat tolerance of those accessions was ranked by principal component analysis (PCA) based on eight phenotypic and physiological traits. Among these traits, electrolyte leakage (EL), chlorophyll content (Chl), relative water content (RWC) had high correlation coefficients (- 0.858, 0.769, and 0.764, respectively) with the PCA ranking of heat tolerance. We also found expression levels of four Chl catabolic genes (CCGs), including LpNYC1, LpNOL, LpSGR, and LpPPH, were significant higher in heat sensitive ryegrass accessions then heat tolerant ones under heat stress. Furthermore, 66 pairs of simple sequence repeat (SSR) markers were used to perform association analysis based on the PCA result. The population structure of ryegrass can be grouped into three clusters, and accessions in cluster C were relatively more heat tolerant than those in cluster A and B. SSR markers significantly associated with above-mentioned traits were identified (R2 > 0.05, p < 0.01)., including two pairs of markers located on chromosome 4 in association with Chl content and another four pairs of markers in association with EL.

Conclusion: The result not only identified useful physiological parameters, including EL, Chl content, and RWC, and their associated SSR markers for heat-tolerance breeding of perennial ryegrass, but also highlighted the involvement of Chl catabolism in ryegrass heat tolerance. Such knowledge is of significance for heat-tolerance breeding and heat tolerance mechanisms in perennial ryegrass as well as in other cool-season grass species.

Keywords: Genetic diversity; Heat tolerance; Leaf senescence; Perennial ryegrass; SSR.

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Conflict of interest statement

The authors declare that they have no conflict of interest.

Figures

Fig. 1
Fig. 1
Heatmap and hierarchical clustering for physiological and morphological parameters under control and heat stress conditions in 98 ryegrass accessions after 24 d of treatment. Abbreviations: WUE, water use efficiency; Pn, photosynthesis rate; RA, root activity; Chl, chlorophyll content; RWC, leaf relative water content; Fv/Fm, photochemical efficiency; PH, maximum plant height; LW, leaf width
Fig. 2
Fig. 2
Principal component analysis biplot of the heat stress index (HSI) of 98 ryegrass accessions. Arrows represent physiological and morphological traits with various lengths based on the impact of each trait on the separation of accessions. Accessions marked with green color in group i and red color in group ii are the ten most and least heat tolerant genotypes, respectively. Abbreviations: WUE, water use efficiency; Pn, photosynthesis rate; RA, root activity; Chl, chlorophyll content; RWC, leaf relative water content; Fv/Fm, photochemical efficiency; PH, maximum plant height; LW, leaf width
Fig. 3
Fig. 3
Phenotype of the five most and least heat tolerant ryegrass accessions. Pictures were taken after 24 d of treatment. Bar in each photo represents 6.5 cm in length
Fig. 4
Fig. 4
Relative expression levels of four CCGs of the five most and least heat-tolerant ryegrass accessions. Relative expression levels of LpNYC1 (a), LpNOL (b), LpSGR (c), and LpPPH (D). Represented data were means and standard error (n = 4)
Fig. 5
Fig. 5
Neighbour-joining tree of 98 perennial ryegrass accessions based on SSR markers
Fig. 6
Fig. 6
Manhattan plots of the general linear model (GLM) for association analysis between SSR markers and each physiological trait. The –log10(P-values) from each SRR markers are plotted against eight heat tolerance-related traits, including TQ, Fv/Fm, Chl content, Pn, WUE, RWC, RA, and EL. NA, not known
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