Genetic Analysis And Fine Mapping Genes Associated With Leaf Rolling In Rice

Semi-rolled leaf is one of the most important morphological characters in plant breeding. Many high yield varieties or their hybrids were semi-rolled leaf cultivars, such as Peiai64s, E32, Lunhui422. A series of studies on effects of leaf rolling on photosynthetic physiology and yield trait all showed that semi-rolled leaf had some upstanding effects, for instance making leaf erect, optimizing canopy light transmission, increasing effective leaf area per unit land, improving the quality of population in late growth stage.However, leaf rolling in rice appeared to be a complex trait since different cultivars had different leaf rolling degrees. Some of them rolled slightly, some rolled moderate, and others rolled cylindrically. Furthermore, there were no reports about fine mapping or cloning of genes for leaf rolling until now.Therefore, two representative varieties were selected to study, one of which was 91SP068, a semi-rolled mutant from progenies of protoplasm culture of Mabelle, and the other was JZB, a NIL of Zhenshan97 carried a major gene for leaf rolling from Liugangjuanyej. The results of genetic analysis and fine mapping of genes controlling leaf rolling related to these two varieties were reported as following: 1. Fine mapping of a major gene rl(t) for leaf rollingFor genetic analysis of leaf rolling, three populations (BC4F2, BC5F1, BC4F3) were derived from a cross between QMX a non-rolled leaf variety as a recurrent parent, and JZB, as a donor parent carried genes for leaf rolling.In BC4F2 and BC4F3 populations, three apparent phenotypes of flag leaf were non-rolled, semi-rolled and rolled, which of them rolled leaf plants could be easily identified from the others. While in BC5F1 population, there were two phenotypes of flag leaf, semi-rolled leaf and non-rolled leaf. The segregation ratio of different phenotypes showedgoodness of fit for the ratio of single Mendelian segregation (non-rolled leaf: semi-rolled leaf: rolled leaf ≈ 1:2:1 in BC4F2 and BC4F3; semi-rolled leaf: non-rolled leaf ≈1:1 in BC5F1). Genetic analysis indicated that rolled leaf of JZB was controlled by one major gene. In addition, the morphology and the leaf rolling index (LRI) of semi-rolled leaf plants were close to that of non-rolled leaf plants. Therefore, the gene from JZB was a recessive gene, termed rl(t)BC4F2 population with 241 plants was constructed to map gene for leaf rolling. First, twenty typical rolled leaf plants and twenty non-rolled leaf plants from BC4F2 were selected to build rolled leaf and non-rolled leaf DNA bulk, respectively. Then, eight polymorphic markers located on chromosome 2 were screened from 500 SSR markers and 15 developed insert/delete (INDEL) markers by bulked segregation analysis (BSA), and a genetic linkage map was constructed by MAPMAKER/EXP3.0. QTL analysis was achieved by composite interval mapping conducted with WinQTLcart2.5. Based on the segregation data of BC4F2 population, rl(t) was primarily mapped between two markers INDEL112 and RM3763, away 1.0 cM from INDEL112 . Furthermore, the result of progeny test of some BC4F2 plants was consistent with the mapping result.To fine map rl(t), one BC4F3 population with 855 plants was generated from a semi-rolled leaf plant in BC4F2, which genotypes of marker flanking rl(t) were heterozygote. In addition, new INDEL markers were developed by blasting the sequence of PAC covering rl(t) of the japonica variety Nipponbare (http://rgp.dna.affrc.go.jp/) to that of the indica variety 93-11 online, and four of them showed polymorphism between two bulks. These four markers with other four markers screened in preliminary mapping were then used to survey the total of 191 rolled leaf plants in BC4F3. Their linkage relationship showed that two markers of them, INDEL112.6 and INDEL113, were inserted into the region between markers INDEL112 and RM3763. Of 191 rolled leaf plants, there was only 1 recombinant between INDEL113 and rl(t) , 5 recombinants between INDEL112.6 and rl(t), and far away from INDEL112.6 and ENDEL113, more recombinants occurred, indicating that...