蓖麻遗传图谱构建及单雌性状基因/QTL定位分析

Pistillate character was the main approach for heterosis in castor bean(Ricinus Communis L.). It had been reported that the pistillate character in castor bean was controlled by either single nuclear recessive gene or multiple nuclear recessive genes or single nuclear dominant gene, which could be used to partially explain the genetic phenomena of pistillate character, whereas could not reveal its genetic law. Consequently, the instability of pistillate line in pistillate character expression, low purity of hybrid and high cost in hybrid seed production have been puzzling. Our experiments showed that, firstly, the pistillate character was controlled by multiple nuclear recessive genes with additive and duplicate effect simultaneously, single nuclear gene with epistatic dominance and polygene together, so the female/male ratio of individuals distributed continuously with multiple kurtosis in segregative generation and the kurtosis moved between generations. Secondly, the stablity of pistillate line was determined by the accumulation of pistillate genes and whether it could be restored rested with the existence of redundant pistillate genes in pistillate line. Lack of the information about the number, location and effect of those genes, which caused the low maneuverability in breeding, it is necessary to research further. This project was planned to construct dense genetic map of castor bean, map the gene/QTLs conferring the pistillate character with immortalized F2 population (IF2), and then fine map them with near-isogenic lines (NILs) to confirm their number and effect, clarify the interaction between them, reveal the genetic law concerning the pistillate character, facilitate raising the purity of hybrid and lowering the cost of hybrid seed production.

单雌性是蓖麻杂种优势利用的主要途径，已有单隐性核基因、多隐性核基因和单显性核基因三种遗传方式报道。由于缺乏对性状数量特征的研究，以上结果都不能解释全部遗传现象。雌性系稳定性差、杂种纯度低和制种成本高是蓖麻育种亟待破解的难题。本小组试验表明：不同遗传背景的材料，其单雌性由积加和重叠效应并存的多对隐性基因、单显性上位基因和多基因共同控制，植株雌雄比在分离世代呈连续的多峰分布，世代间有"峰移"现象；雌性系的稳定性主要取决于单雌基因的积累和上位基因的存在，"冗余单雌基因"是雌性系后代育性难以恢复的真正原因。为进一步获得准确的基因数目、位置和效应信息，增强育种操作性，特开展本项研究。本项目拟用永久F2群体构建蓖麻的遗传图谱、定位单雌性状基因/QTLs，进而用近等基因系精细定位之，确定单雌关键基因的数目和效应，阐明基因间的相互作用，揭示单雌性状的遗传规律，为提高蓖麻杂种优势利用水平提供理论支持。

蓖麻是重要的油料作物。由于遗传研究相对滞后，影响了育种水平的提高，品种产量低是制约蓖麻产业发展的最重要因素。利用雌性系培育杂交种是国内外蓖麻育种的主要方向，但由于对雌性系（俗成单雌性状）遗传规律不明，造成杂交种纯度不高，优势不明显。本研究利用基因组测序信息，开发蓖麻微卫星分子标记（SSR）2719对，发现蓖麻基因组中SSR的密度为15.81个/Mbp，二核苷酸重复和三核苷酸重复类型为主，尤以 (AT)n 和 (AAT)n最为普遍， SSR的频率随着重复单元的增大而减小；构建了蓖麻的第一张遗传图谱，含331个标记，覆盖基因组1164.73 cM ，标记平均间距3.63 cM.；用3个F2群体对单雌性状进行了定位， 共检测到QTL16个，分别解释了74.51%,、41.71% a和48.98% 的总变异，其中一个在三个群体中同时被检测到，另一个在两个群体中被同时检测到。互作效应在两个群体中分别解释了29.78% 的26.24% 的总变异。同时检测到3个镶嵌雄花性状QTL。为了弥补超强台风“威马逊”和“海鸥”袭击重组自交系造成的严重损失，采用F2群体群体进行SLAF (Specific Length Amplified Fragment) 简化基因组测序，构建了一张高密度遗传图谱，并用该图谱对单雌性状进行了定位。该图谱含SLAF 标记4300个，SSR标记122个，覆盖基因组1,547.41cM，标记间平均间距0.35cM，定位到QTL 6个，其中3个是再次被检测到的，共解释了46.8%的总变异。综合表型遗传分析和QTL定位结果，得出以下结论：蓖麻单雌性状由兼具累加效应和重叠效应的若干隐性主基因、至少一对显性上位基因和多基因共同控制；单雌性状必须有足够的隐性单雌基因才能表现，如果超过，表型仍为单雌，但恢复系必须有额外的恢复基因来克服这些冗余单雌基因才能恢复育性。单雌的表现还需要显性上位基因的存在，否则单雌株会表现出镶嵌雄花。单雌基因和显性上位基因都受微效基因修饰。遗传图谱的构建为蓖麻基因定位、分子育种及比较基因组研究等奠定了基础，单雌性状遗传规律的揭示，不仅为蓖麻核三系杂种优势利用提供了理论支持，也可为单性花植物育性研究提供了参考。