堆疊白葉枯病抗病基因座對水稻甲烷排放量及根部微生物相之影響

Abstract

亞洲稻米生產以湛水栽培為主，低氧狀態使土壤中的厭氧微生物大量增殖，包括產甲烷菌，因此水稻田為全球甲烷排放的主要來源之一。白葉枯病為嚴重威脅稻米生產之病害，目前已鑑定出數十個抗病基因座並堆疊至不同稻品系，先前有研究指出抗病基因的導入會影響水稻的代謝體，但目前仍不清楚是否會影響根內及根圈菌相組成，因此本研究企圖探究白葉枯病抗病基因的導入對根圈、根內細菌結構及甲烷排放的影響。本研究以堆疊5個抗病基因座的品系IRBB66及其母本IR24，以及IRBB66導入TNG82的品系為材料，調查水稻的甲烷排放量與根系結構、根圈及根內菌相、根分泌物的差異。2023年一期作的調查發現，各品系的甲烷排放速率隨生育時期演進和環境溫度增加而提升，在乳熟期IRBB66及其導入系的甲烷排放速率皆比輪迴親本低；根系結構的分析顯示IRBB66和導入系的根尖數、根長、根表面積較親本低，顯示根系並不是影響甲烷排放的關鍵。根圈菌相分析發現IRBB66較IR24更能吸引產甲烷菌，但在根內生菌相的部分則發現導入白葉枯病抗病基因座的品系吸引較多甲烷氧化菌到根內，可能是造成導入系的甲烷排放量少於親本的原因；根分泌物組成的分析結果發現部分長鏈脂肪酸和有機化合物在IR24的根分泌物中含量顯著較高，仍需進一步試驗以確認這些化合物與菌相的相關性，未來會持續觀察不同期作抗病品系與親本的甲烷排放，以及探究品系間的通氣組織及地上部的性狀差異，以期了解白葉枯病抗病基因座對甲烷排放之影響，作為未來育成抗病和低碳排品系之參考。

Paddy cultivation is the main agricultural practice for Asian rice production, which generates low oxygen environment that promote the proliferation of anaerobic microorganisms in soil, including methanogenic archaea. Thus, rice paddies are the one of human sources of methane emissions. Bacterial blight (BB) is a serious threat to rice production. Numbers of loci associated with disease resistance have been identified and stacked into different rice varieties. It has been shown that the introducing disease resistance genes affects plant metabolome, but it remains unclear whether it influences the composition of endospheric or rhizospheric microbiome. Thus, this study aims to explore the impacts of pyramiding bacterial leaf blight resistant genes on rhizospheric and endospheric bacterial structure and methane emissions. IRBB66 line, which stacks five BB-resistant genes and the introgressive lines in TNG82 were recruited as materials for investigating the differences of methane emissions, root structure, rhizospheric and endospheric bacterial communities, and root exudate composition between lines. In the first cropping season in 2023, we found that methane emissions rates of all the lines increased with the progression of the growth period and environmental temperatures. During the milky stage, methane emission rates of IRBB66 and its introgressive lines were lower than those of recurrent parents. Root structure analysis showed that the number of root tips, total root length, and root surface area of IRBB66 and its introgressive lines were lower than those of recurrent lines, suggesting that root structure may not be the key factor affecting methane emissions. Rhizosphere microbiome analysis revealed that IRBB66 attracts more methanogens compared to IR24, but in endospheric microbiome, BB-resistant lines attracted more methanotrophs to roots. It may be one of the reasons that the disease-resistant lines had less methane emissions. Analysis of root exudate profiles suggested that some long-chain fatty acids and some organic compounds in IR24 were higher than in IRBB66. Further experiments are required to confirm the roles of these compounds in modulating bacterial structure in rhizosphere and endosphere. In the future we will keep monitering the methane emissions of BB-resistant and parental lines. The difference of aerenchyma structure and physiological traits of aboveground tissues will be also dissected. The results will help to understand the impacts of introducing BB-resistant genes on rice methane emission and provide useful information for developing disease-resistant and low-carbon-emission lines in the future.