Morphogenetic mechanism regulating phyllochron in rice

在牧草中，依序生长的叶片和分蘖芽的形态发生过程是非常规则的，导致了与连续叶片的出现相关的枝条系统的有序发展。因此，连续叶片出现之间的间隔，或叶轮，被广泛用作量化牧草发育和生长的时间单位。多年生草本植物品种间的遗传变异早已被人们所认识。然而，影响叶轮的特定遗传因素尚未确定。本研究的目的是寻找控制水稻叶轮的数量性状基因座。我们利用了两个优良品种Lemont(粳稻)和IR36(籼稻)的杂交F_2群体。柠檬和IR36的苗期平均为每叶4.0d和3.1d。F_2的表型范围在亲本范围内。区间作图检测到位于第1、2、9和11染色体上的5个QTL，这些QTL分别解释了表型变异的8%~16%。在这些QTL上，Lemont等位基因的存在增加了叶轮，除了9号染色体上的Lemont等位基因减少了叶轮。这些结果表明，叶轮是由多个QTL控制的，而不是由一个主基因系统控制的。根据水稻和玉米基因组的同源性，玉米末端穗1基因的同源基因被认为是1号染色体上QTL的候选基因。

Morphogenetic processes in sequentially growing leaves and tiller buds are highly regular in grasses, resulting in the ordered development of the shoot system in relation to the appearance of successive leaves. Thus, the interval between appearance of successive leaves, or phyllochron, has been used extensively as a time unit to quantify the development and growth of grasses. Genetic variation in phyllochron has long been recognized among grass cultivars. However, specific genetic factors influencing the phyllochron have not been identified. The objective of this study was to identify quantitative trait loci (QTLs) controlling phyllochron in rice. We used F_2 population from a cross between two elite cultivars, Lemont (japonica) and IR36 (indica). Phyllochrons for seedlings of Lemont and IR36 averaged 4.0 and 3.1 days per leaf, respectively. The range of the F_2 phenotype was within that of the parental values. An interval mapping detected five QTLs located on chromosomes 1, 2, 9, and 11. Individually, these QTLs accounted for 8 to 16% of the phenotypic variation. At these QTLs, the presence of a Lemont allele increased phyllochron, except for the QTL on chromosome 9 where the Lemont allele decreased phyllochron. These results demonstrate that phyllochron is controlled by multiple QTLs rather than by a major gene system. Based on the synteny between rice and maize genomes, the ortholog of the maize terminal ear 1 gene was considered to be a candidate gene for the QTL on chromosomes 1.