Heat Tolerance,QTL Mapping And Its Candidate Genes Analysis At The Flowering Stage In Rice

In recent years,global climate change is becoming more and more serious,and extreme high temperature weather is more and more frequent.High temperature has become one of the most important abiotic stresses threatening the safety of rice production.The results showed that flowering stage was the most sensitive period to temperature change,and it was also the most critical stage to determine grain yield.Therefore,it is of great strategic significance to study the physiological mechanism of heat tolerance at flowering stage,identify the heat tolerance of different rice genotypes,explore the heat tolerance gene resources of rice,and cultivate new heat tolerance varieties to cope with the threat of climate warming.Based on the relationship between accumulated temperature of high temperature damage and relatively spikelet fertility of rice,this study explored the identification method of heat tolerance of rice and identified and evaluated the heat tolerance of different rice varieties;identified the physiological mechanism of heat tolerance at flowering stage by the different response of different heat tolerant rice varieties to high temperature;carried out the Q-test of heat tolerance at flowering stage by the genetic population obtained from the cross of heat tolerant varieties and high temperature sensitive varieties TL mapping can provide theoretical basis and donor materials for breeding of heat-resistant rice varieties.The main results are as follows:1.Identification method for heat resistance at the flowering stage in riceGuiliangyou 2,liangfengyou 339 and N22 were used as research materials,and the plants growing under natural conditions were used as control.Different high temperature treatments(35 and 38?)and duration(2,4,6,8 and 10 days)were set in a phytotron.High temperature treatments were carried out at flowering stage of rice,and the relative spikelet fertility(RSF)under high temperature treatment was calculated after maturity.The result showed that there was a negative exponential relationship between accumulated temperature of high temperature(T_a)and RSF(RSF=117.9·e^-0.01Ta,R²=0.82^*,P<0.05)with 32?as the critical temperature of high temperature damage.Combined with the flowering habit of rice,the difference of heat tolerance among different rice genotypes could be identified and distinguished scientifically and effectively by treating at 38?for 6 hours(9:30-15:30)per day for 3 days at the flowering stage in rice.2.Evaluation of heat tolerance at the flowering stage for different rice varietiesThe heat tolerance of 100 different rice genotypes was evaluated by simulating high temperature stress at flowering stage in a phytotron,with the seed setting rate and relative seed setting rate under high temperature stress combined with yield as evaluation indexes.The result showed that there were significant differences in heat tolerance and yield potential among different rice genotypes,Teyou 837,Yunguang 14,Q You 8,Guodao 7,Y Liangyou865,Shanyou 63 and Huanghuazhan were heat-tolerant cultivars with a high yield;OM4900,882H and 93-11 were heat-sensitive varieties.3.Physiological mechanism of heat tolerance at the flowering stage in riceIn this study,the spikelet fertility percentage in high-temperature tolerant YLiangyou 1(YLY1)was higher than that of high-temperature sensitive Liangfengyou 339(LFY339).The net photosynthetic rate and SPAD in flag leaf were declined under high temperature stress,compared with high-temperature sensitive LFY339,the high-temperature tolerant YLY1could keep higher photosynthetic ability under high temperature stress.The soluble sugar,soluble protein and proline content in flag leaf were decreased under high temperature stress,but heat stable protein content increased.The increase scope of malonyldialdehyde(MDA)content and membrane permeability in high-temperature sensitive varierty LFY339 was more significant under high temperature stress than in high temperature tolerant varierty YLY1.Under high temperature stress,higher photosynthetic characteristics and SPAD,soluble protein,proline and lower MDA content in rice flag leaf were the physiological basis of high-temperature tolerant rice cultivar.4.QTL mapping and identification of candidate genes for heat tolerance at the flowering stage in riceIn this study,the F_2:3 population derived from a cross between Huanghuazhan(HHZ),a heat-tolerant cultivar,and 9311,a heat-sensitive variety,was used to map heat tolerance QTLs during the flowering stage in rice.A new major QTL,q HTT8,controlling heat tolerance at the flowering stage was identified on chromosome 8 using the bulked-segregant analysis(BSA)-seq method.The QTL q HTT8 was mapped into the 3555000–4520000 bp,which had a size of 0.965 Mb.The candidate region of q HTT8 on chromosome 8 contained 65 predicted genes,and ten putative predicted genes were found to be associated with abiotic stress tolerance.Furthermore,q RT-PCR was performed to analyze the differential expression of these 10 genes between HHZ and 9311 under high temperature conditions.LOC?Os08g07010and LOC?Os08g07440 were highly induced in HHZ compared with 9311 under heat stress.Orthologous genes of LOC?Os08g07010 and LOC?Os08g07440 in plants played a role in abiotic stress,suggesting that they may be the candidate genes of q HTT8.Generally,the results of this study will prove useful for future efforts to clone q HTT8 and breed heat-tolerant varieties of rice using marker-assisted selection.