在低光照環境下綠豆、根瘤菌與叢枝菌根菌三者間的共生交互作用

The tripartite symbiotic interaction among Vigna radiata, rhizobia, and arbuscular mycorrhizal fungi under low light environment

田上穎(Shang-Ying Tien)

指導教授 ： 李承叡

國立臺灣大學/生命科學院/植物科學研究所/碩士(2021年)

https://doi.org/10.6342/NTU202103767

摘要

生物在適應的環境的過程中，發展出與其他生物合作的模式，提高自身的生存率，稱之為共生。共生往往受到生物體精細的調控，不同的環境甚至會打破生物間原本的共生關係。植物與其他生物也存在著古老的共生關係，如叢枝菌根菌 (arbuscular mycorrhizal fungi) 可以為宿主提供磷，而根瘤菌 (rhizobia) 可以為豆科植物固氮。豆科植物-根瘤菌-叢枝菌根菌形成三者共生時往往可以幫助豆科植物的生長，但在嚴苛的環境下，三者之間的共生關係是否還能繼續維持?還是會有一種生物變身成寄生生物呢?本篇研究著重於探討三者共生的關係在低光源且營養缺乏的環境中是否會破局，以及兩個綠豆亞種對於兩種土壤共生菌的共生反應是否有所不同。為了盡量涵蓋全球各地的綠豆基因型，我們選用了10個綠豆品系，橫跨野生型綠豆 (Vigna radiata ssp. sublobata) 與栽培型綠豆 (V. radiata ssp. radiata) 的四個族群，含東亞、中亞、南亞、東南亞族群。單獨接種根瘤菌顯著提升兩個綠豆亞種的生長狀況，而單獨接種叢枝菌根菌反而使綠豆生物量下降。共同接種兩種土壤共生菌後，綠豆的生長狀況與單獨接種根瘤菌的情狀相似。另外根瘤菌在共生後期顯著地提升綠豆的相對葉綠素含量。在探討總根瘤鮮重與植物性狀關係的分析中，發現隨著總根瘤鮮重的上升，植物性狀大多都會跟著提升，而叢枝菌根菌的存在則使相關性下降。五個野生型綠豆品系皆會與根瘤菌形成根瘤，栽培品系綠豆則顯示出不同的結果：西亞和中亞族群形成極多根瘤而南亞與東南亞族群卻無法或形成少數根瘤。叢枝菌根菌則廣泛地與所有綠品系豆形成共生構造。我們發現根瘤菌可以提升叢枝菌根菌的適應力，而叢枝菌根菌則會使根瘤菌的適應力下降。後續我們擴增至20個綠豆品系測試跟兩種根瘤菌 (Bradyrhizobium japonicum 和 Enifer fredii) 是否會呈現不同的專一性，結果顯示E. fredii對綠豆具有較明顯的宿主專一性，並且專一性與綠豆的族群結構無關。另外B. japonicum對20個品系的綠豆在相對葉綠素含量上相較有E. fredii對更顯著的促進作用。綜合來說，在低光照低養分的環境下對於綠豆來說根瘤菌是較佳的共生夥伴，叢枝菌根菌更像一個寄生生物。

關鍵字

綠豆 ； 根瘤菌 ； 叢枝菌根菌 ； 共生 ； 多重共生效應 ； 遺傳力 ； 適應力

並列摘要

In the process of adaptation to the environment, organisms develop a mode of cooperation with other organisms to improve their own survival rate, which is called mutualism or symbiosis. The symbiosis systems are so elaborate that may be broken as the environment changes. Ancient symbiotic relationships exist between plants and other organisms, such as arbuscular mycorrhizal fungi (AMF), providing phosphorus (P) to the host plants, and rhizobia (RH), fixing nitrogen (N) for legumes. All three parties could benefit from the tripartite symbiosis. However, would the tripartite symbiosis still work as usual under adverse conditions? Would one of the organisms would turn into parasite? The aim of the study is to find out whether the symbiotic response of two mung bean subspecies to the two soil microorganisms is different. To represent worldwide genetic variation, we chose 10 mung bean (Vigna radiata) accessions including wild mung beans (V. radiata ssp. sublobata) and four groups of cultivars (V. radiata ssp. radiata) from East Asia, Central Asia, South Asia, and Southeast Asia. In terms of plant growth, both mung bean subspecies were promoted when inoculated with RH but not with AMF, which even decreased plant biomass. Dual inoculation showed almost the same pattern as the RH-only treatment. Furthermore, RH significantly improved relative chlorophyll content in the later stage. In the analysis of correlation between total nodule fresh weight and plant traits, most plant traits have positive correlation with total nodule fresh weight, but the presence of AMF attenuates such relationship. Wild accessions could form nodules with Bradyrhizobium japonicum while cultivars performed different patterns, where accessions from East Asia and Central Asia formed many nodules but accessions of South Asia and Southeast Asia group formed no or few nodules. Compared to RH, AMF could broadly form symbiosis with all mung bean accessions. We found that RH could increase AMF fitness while AMF decreased RH fitness. To investigate whether specificity to RH was related to genetic structure, we extended to 20 accessions for the inoculation of two RH species (B. japonicum and Enifer fredii). We found that E. fredii has obvious host specificity, and B. japonicum has a more significant promotion effect on the relative chlorophyll content of 20 mung bean accessions than E. fredii. In conclusion, rhizobia seem to be a better partner than AMF, and AMF appears to be a parasite under low light and nutrient-deficient environments.

並列關鍵字

Vigna radiata ； rhizobia ； arbuscular mycorrhizal fungi ； mutualism ； multiple mutualist effects ； heritability ； fitness

參考文獻

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