Morphogenetic mechanism regulating phyllochron in rice

在禾本科植物中，连续生长的叶片和分蘖芽的形态发生过程是非常有规律的，从而导致与连续叶片的出现有关的芽系统的有序发育。因此，连续叶子出现的间隔，或叶时，已被广泛用作时间单位来量化草的发育和生长。叶时的遗传变异在禾本科品种中早已被认识。然而，影响叶时的特定遗传因素尚未确定。本研究的目的是鉴定控制水稻叶时的数量性状位点。本研究以两个优良品种Lemont（粳稻）和IR36（籼稻）杂交的F_2群体为材料。Lemont和IR 36幼苗的叶时平均分别为4.0和3.1天/叶。F_2代的表型范围在亲本范围内。区间作图检测到5个QTL，分别位于第1、2、9和11染色体上。这些QTL分别占表型变异的8%~16%。在这些QTL中，Lemont等位基因的存在增加了叶时，除了9号染色体上的QTL，其中Lemont等位基因减少了叶时。这些结果表明，叶时是由多个QTL控制，而不是由一个主基因系统。基于水稻和玉米基因组间的同线性，玉米顶穗1基因的直系同源物被认为是第1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.