Gene Mapping Of TSV8 Gene For Chloroplast Development Under Low Temperatures In Rice

Rice is one of the main foods for people in South China.In this study,a rice thermo-sensitive virescent mutant,tsv8 was derived from japonica variety‘Jiahua No.1’treated by EMS.Then,these were carried out the analysis of physiological characteristics,map-based cloning,and relevant functional analysis.The main conclusions were as follows:1.Through analyzing the physiological characteristics of the tsv8 mutant and WT under six-type temperatures,the mutant tsv8 exhibited the albino phenotype and eventually died after the 4-leaf stage under the low temperatures（at 20℃）.However,with the cultural temperature increasing,the leaf color of the mutant tsv8 gradually turned green.When the mutant tsv8 was cultivated at 32℃,the leaf color returned to normal green as the same as WT.2.The photosynthetic pigments contents of mutant tsv8 and WT were detected under the different temperatures.The leaves color phenotype of mutant tsv8 were closely related to photosynthetic pigments contents.At the low temperatures,the leaves color phenotype of the mutant tsv8 exhibited an albino phenotype,while its photosynthetic pigments contents were significantly down-regulated compared with the WT.As the temperature increased,the leaves color of the mutant tsv8 changed to green,and the contents of photosynthetic pigment also recovered.At 32℃,the photosynthetic pigment contents of the mutant tsv8 were consistent with the WT.3.The F₂population dated from the cross between the mutant tsv8 and Peiai 64S with used as genetic analysis.It was found that the F₂population had character segregation.The segregation ratio of green and white leaves was conformed to the segregation law with 3:1,which indicated that the leaf color trait of low thermo-sensitive virescent mutant was controlled by a recessive nuclear gene TSV8.4.Then,TSV8 gene was further mapped between the range of ID08M03982 and ID8M04021 on chromosome 8 using DNA molecular markers,with a physical distance of 67kb.By sequencing,it was found that the gene LOC＿Os08g09270（TSV8）outside the third exon with base C was replaced by another base T,leading to the mutant tsv8 leaves phenotypic albinism at low temperature.5.Transcriptional level analysis illustrated that the mutation of the TSV8 gene resulted in a down-regulation of chloroplast development related genes at low temperature,while there was no significant difference between tsv8 mutant and WT on the expression of genes related to chloroplast development at high temperature.In this study,we found that TSV8 gene might be a new thermo-sensitive virescent gene encoding pentapeptide protein in rice.It was an essential gene for chloroplast development at low temperature.It inhibited the physiological metabolic response and normal chloroplast growth of the mutant at low temperature.This study could provide research materials for the genetic improvement of low temperature tolerance in rice under low temperature stress.