Identification and gene mapping of a grain-fillingmutant gef1 in rice
2016
Grain filling is an extremely important process in rice growth
and development. This process which involves complex genetic regulatory
networks and environmental interaction, is directly related to the
formation of rice yield and quality. A stable inherited mutant with
grain extended filling ( gef1 ) was identified from
an EMS mutagenized population of Yixiang 1B. The investigation of
agronomic traits, measurement of physiological and biochemical characteristics,
histology observation, gene expression analysis and gene mapping were
performed in this study. Compared with the wild type plants, the grain
filling rate of gef1 was significantly lower than
that of Yixiang 1B, resulting in the grain filling time of gef1 was about 30 days delay. Meanwhile, the 1000-grain
weight of gef1 became bigger and seed setting rate
decreased by 22%. During the development of caryopsis, we found that
the soluble sugar content in wild type showed a single peak curve,
and the content maintained at a low level throughout the grain filling
stage. However, the soluble sugar content of the gef1 was significantly higher than that of the wild type, and showing
a bimodal curve. It revealed that the transportation and distribution
of photosynthate, and starch synthesis were inefficiency
in gef1 . In addition, histocytological analysis showed
that the number of big vascular bundles in the same transection parts
of rachis, the first top internodes and the second top internodes
were all decreased in gef1 , and indicated that the
transport efficiency of photosynthate was one of the limiting factors
in the rate of grain filling. The scanning electron microscope showed
that the glume of gef1 had smooth surface and slender
cells. Scanning of grain transection showed that gef1 had spherical amyloplasts and arranged loosely, but the wild type
had unregular polygon amyloplasts and packed closely. These results
suggested that the changes of grain size associated with the cell
number and shape of glume, and gef1 had impact on
rice quality. Additionally, by analyzing the expression of the glycometabolism-related
genes in developing caryopsis, we found that all of them were keeping
at a low level in gef1 compared with the wild type.
By analyzing the three crosses gef1 /Yixiang 1B, gef1 /02428 and gef1 /Kitaake, we found that
the F 1 plants of these three crosses were all normal and
indicated that the mutant trait was controlled by a recessive gene.
The ratio of normal plants to mutant plants in the three F 2 populations was 3:1 and indicating that the mutant trait was controlled
by a single recessive nuclear gene. gef1 was preliminarily
mapped on the short arm of rice chromosome 3, and was narrowed to
a 198 kb region between InDel3-1 and InDel3-2. This region has 21
open reading frames and there was no homologous gene had been reported
within it, and the further identification work of candidate genes
is ongoing.
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