Significant achievements have been made in breeding programs for the heavy panicle-type (HPT) rice (Oryza sativa) in Southwest China. The HPT varieties now exhibit excellent lodging resistance, allowing them to overcome the greater pressures caused by heavy panicles. However, the genetic mechanism of this lodging resistance remains elusive. Here, we isolated a major quantitative trait locus, Panicle Neck Diameter 1 (PND1), and identified the causal gene as GRAIN NUMBER 1A/CYTOKININ OXIDASE 2 (Gn1A/OsCKX2). The null gn1a allele from rice line R498 (gn1a R498) improved lodging resistance through increasing the culm diameter and promoting crown root development. Loss of function of Gn1a/OsCKX2 led to cytokinin accumulation in the crown root tip and accelerated the development of adventitious roots. Gene pyramiding between the null gn1a R498 allele with two gain-of-function alleles, STRONG CULM 2 (SCM2) and SCM3, further improved lodging resistance. Moreover, Gn1a/OsCKX2 had minimal influence on overall rice quality. Our research thus highlights the distinct genetic components of lodging resistance of HPT varieties and provides a strategy for tailor-made crop improvement of both yield and lodging resistance in rice.
隨著城市化的發(fā)展，耕地面積不斷減少、勞動(dòng)成本日益攀升，機(jī)插與直播等精簡(jiǎn)化栽培技術(shù)在水稻生產(chǎn)中得到廣泛的推廣運(yùn)用，同時(shí)由于大量化肥的使用，使水稻倒伏日益嚴(yán)重。水稻倒伏不僅會(huì)導(dǎo)致收獲成本增加，還會(huì)造成產(chǎn)量和品質(zhì)嚴(yán)重下降。因此，生產(chǎn)上急需抗倒伏能力強(qiáng)的優(yōu)良水稻品種。重穗型超高產(chǎn)雜交稻育種是針對(duì)西南稻區(qū)“寡日照、高濕度、低溫差”的生態(tài)條件提出的育種理論。相關(guān)品種在中國(guó)西南部廣泛種植，為保障我國(guó)的糧食安全做出了巨大貢獻(xiàn)。重穗型水稻品種表現(xiàn)出優(yōu)良的抗倒伏能力，使其能夠克服“大而重”的穗部造成的壓力。然而，重穗型水稻抗倒伏的遺傳機(jī)制尚不清楚。
四川農(nóng)業(yè)大學(xué)李仕貴教授團(tuán)隊(duì)選育的西南雜交稻骨干親本蜀恢498，每穗粒重高達(dá)6克，但仍具有良好的抗倒性。利用蜀恢498和宜恢3551構(gòu)建的重組自交系進(jìn)行抗倒伏QTL定位分析，克隆到一個(gè)主效QTL位點(diǎn)，qPND1。基因精細(xì)定位與遺傳互補(bǔ)等試驗(yàn)發(fā)現(xiàn)候選基因?yàn)榧?xì)胞分裂素氧化酶基因OsCKX2/Gn1a。蜀恢498中OsCKX2/Gn1a第三外顯子有11 bp的缺失造成移碼突變且翻譯提前終止。攜帶有gn1aR498型等位基因的植株莖稈直徑、抗折力極顯著高于gn1aR3551植株及互補(bǔ)株系。進(jìn)一步研究發(fā)現(xiàn)OsCKX2/Gn1a不僅影響莖稈的發(fā)育，還在根維管組織中表達(dá)，促進(jìn)不定根的生長(zhǎng)，從而形成更加發(fā)達(dá)的根系。基因聚合分析發(fā)現(xiàn)gn1aR498與優(yōu)良基因SCM2 (STRONG CULM2)和SCM3的聚合能進(jìn)一步增強(qiáng)水稻抗倒伏能力。
前期的研究表明無(wú)功能型的gn1aR498是重穗型水稻品種產(chǎn)量的決定因素，同時(shí)蒸煮食味品質(zhì)分析表明gn1aR498優(yōu)良等位基因在提高產(chǎn)量、增強(qiáng)抗倒伏能力的同時(shí)不影響稻米品質(zhì)。因此，研究成果解析了重穗型雜交稻親本蜀恢498優(yōu)良抗倒伏遺傳機(jī)制，為重穗型水稻高產(chǎn)、抗倒的水稻新品種育種應(yīng)用提供了理論支撐。