Improving crop yield potential through an enhanced response to rising atmospheric CO2 levels is an effective strategy for sustainable crop production in the face of climate change. Large-sized panicles (containing many spikelets per panicle) have been a recent ideal plant architecture (IPA) for high-yield rice breeding. However, few breeding programs have proposed an IPA under the projected climate change. Here, we demonstrate through the cloning of the rice (Oryza sativa) quantitative trait locus for MORE PANICLES 3 (MP3) that the improvement in panicle number increases grain yield at elevated atmospheric CO2 levels. MP3 is a natural allele of OsTB1/FC1, previously reported as a negative regulator of tiller bud outgrowth. The temperate japonica allele advanced the developmental process in axillary buds, moderately promoted tillering, and increased the panicle number without negative effects on the panicle size or culm thickness in a high-yielding indica cultivar with large-sized panicles. The MP3 allele, containing three exonic polymorphisms, was observed in most accessions in the temperate japonica subgroups but was rarely observed in the indica subgroup. No selective sweep at MP3 in either the temperate japonica or indica subgroups suggested that MP3 has not been involved and utilized in artificial selection during domestication or breeding. A free-air CO2 enrichment experiment revealed a clear increase of grain yield associated with the temperate japonica allele at elevated atmospheric CO2 levels. Our findings show that the moderately increased panicle number combined with large-sized panicles using MP3 could be a novel IPA and contribute to an increase in rice production under climate change with rising atmospheric CO2 levels.
大氣CO2含量上升是全球變暖的重要因素之一。隨著溫度上升，頻繁的極端天氣會嚴重影響作物產量。而CO2升高可以提高C3作物的光合效率，如何借助這一氣候變化來提高產量成為未來作物育種的潛在方向。研究表明，增加庫容是高CO2濃度下提高水稻產量的關鍵因素?，F(xiàn)有高產水稻品種進一步擴大穗型已經較難實現(xiàn)，改良穗數成為改良CO2吸收能力的關鍵。
日本農業(yè)科學國際研究中心學者在高產秈稻品種 Takanari和溫帶粳稻品種 Koshihikari形成的近等基因系（NIL）水稻中發(fā)現(xiàn)，攜帶MP3（MORE PANICLES 3）基因的水稻株系NIL-MP3的穗數顯著高于親本品種Takanari。通過精細定位發(fā)現(xiàn)，MP3是OsTB1/FC1的一個天然等位基因。已有研究表明該轉錄因子在水稻分蘗芽生長中起負調控作用。通過多個染色體片段代換系（CSSL）進行比對發(fā)現(xiàn)，MP3等位基因包含三個外顯子多態(tài)性，這三種多態(tài)性的組合會影響水稻穗數。MP3基因的多態(tài)性存在于溫帶粳稻亞組的大多數材料中，但在秈稻亞組中很少觀察到。進一步研究表明，MP3是OsTB1/FC1的溫和等位基因，它能在不減少穗大小和莖稈厚度的情況下選育出大穗型品種。此外，研究人員還發(fā)現(xiàn)，在正常環(huán)境條件下，NIL-MP3的產量與Takanari不相上下；當環(huán)境中CO2水平升高后，NIL-MP3的產量可達到Takanari的1.4倍。由此可見，MP3在高濃度CO2環(huán)境中對稻谷產量提升更加有效。
隨著氣候變化的加劇，作物育種必須不斷適應新的環(huán)境，以保證糧食產量。利用二氧化碳的變化來提高作物產量是一個有前途的方向，而改良穗數可能是實現(xiàn)這一目標的關鍵所在。