水稻不平衡分離基因 SDL6 的精細定位

不平衡分離是指在雜交後代基因型比例偏離期望的孟德爾分定率的一種現象，造成不平衡分離的原因眾多，主要的效應可以分為配子型和合子型。為瞭解台中秈10號與台稉2號雜交的F2分離族群中不平衡分離的現象，本實驗室建立了4個正反回交的試驗族群，並以EM演算法估計不平衡分離基因座的位置及效應。並在第六條染色體上定位到一個來自台中秈10號的強烈雄配子效應基因座SDL6。本篇主要探討的內容為SDL的精細定位以及候選基因功能的討論。首先使用以台中秈10號為背景，第六條染色體置換成台稉2號的全染色體置換系來進行精細定位，利用自交後裔檢定不平衡分離的現象是否持續存在，並隨著世代推進，將SDL6定位在第六條染色體，分子標誌SDL6_26-SDL6_36之間，區間大小為304.6 kb將這段區間區分為兩個部分SDL6_35-SDL6_36與SDL6_26-SDL6_35兩個區間，受限於分子標誌的數量，暫時不考慮SDL6落在SDL6_35-SDL6_36區間中的狀況，而是先鎖定SDL6_26-SDL6_35大小39.5 kb作為本試驗重點。根據RAP-DB所提供的候選基因資料顯示，在這段區間中共有8個候選基因。分析在分子標誌SDL6_26-SDL6_35之間發生重組的個體，並依據候選基因的位置設計SNP的分子標誌來判定該區間的基因型，配合InDel分子標誌進行後裔檢定的結果，將候選基因數目從8個縮小為4個候選基因分別是Os06g0717600、Os06g0717700、Os06g0717800與Os06g0717850。與先前發表的生殖障礙基因的功能不同，SDL6主要是受到花粉管的萌發及生長速度差異進而造成不平衡分離的現象。本實驗結果將有助於SDL6基因的選殖與進一步的功能分析。

關鍵字

水稻；不平衡分離；精細定位；花粉管

並列摘要

Segregation distortion is the deviation of the segregation ratio of a locus from the expected Mendelian ratio. Previous study conducted in our laboratory by using reciprocal backcrosses has indicated that the segregation distortion among progenies derived from a cross of Taichung Sen 10 (indica) and Taikeng 2 (japonica) may be contributed by gametic effect rather than zygotic effect. A segregation distortion locus, SDL6, has been mapped on to the region between RD0612 and RD0613 on chromosome 6. The objectives of this study are to fine map the SDL6 locus to a smaller region so that candidate genes may be found, and to measure the differences of pollen characteristics between plants that have distorted and non-distorted progenies. Started with a chromosomes-segment substitution line D341 with has substituted TK2 in TCS10 genetic background at Chromosome 6 between RD0611 and RD0613, spanning 17 cM, a series of selfing and progeny test has led to a conclusion that the SDL6 locus was located at a region of 304.6 kb, between SDL6_26 and SDL6_36. For lacking markers between SDL6_35 and SDL6_36, we focused on interval SDL6_26-SDL6_35 where only 8 candidate genes are located. In order to locate the segregation breakpoint, 7 sequencing markers are used to partition the 39.5 kb region into 4 smaller portions, and we use these markers jointly with other In/Del makers to reduce the number of candidate genes from 8 to 4, which are Os06g0717600, Os06g0717700, Os06g0717800 and Os06g0717850. Since there is no difference on pollen fertility between distorted and non-distorted plants, it is suspected that the pollen germination rate and pollen tube growth rate are the driving factors for the gametic competition. However, due to the difficulties on measuring these traits, the differences were not statistically significant.