Study Of Histone Demethylases JMJ706 And JMJ707 Function In Rice Reproductive Development

Rice is an important food crop and a model plant for the genomics study of gramineous crops.Rice reproductive development is very important for the yield trait.JMJ706 is a histone demethylase that was previously shown to affect floral organ development in rice.However,it is unclear whether JMJ706 is also involved in other biological processes.In this work we further studied the role of JMJ706 in regulating floral organ development,fertility,plant height and heading date in rice,and its functional redundancy with the homolog JMJ707.The main results are as follows:1.JMJ706 is involved in regulating the development of floral organs.By carefully examining the spikelets of the jmj706 mutant,we found that the mutation of JMJ706 had a greater effect on the number of stigmas than anthers.In addition,the mutation of JMJ706 also resulted in abnormal glume development,mainly manifested as palea defect and increased glume in some spikelets.To further study the function of JMJ706 on floral organ development,we produced two types of complementary lines: one with the wild type JMJ706 gene,the other with a mutation in the catalytic domain of the gene,and found that the mutant version of the gene could not complement the abnormal floral phenotype of the jmj706 mutant,suggesting that the demethylase function was required to complement the phenotype..2.JMJ706 is involved in the regulation of male gamete development.We found that the seed setting rate of the jmj706 mutant was significantly reduced.Reciprocal crosses showed that the male gamete fertility of jmj706 was decreased,which may be the cause of the seed setting rate decreaseof the mutant.The pollen fertility of jmj706 was further verified by pollen grain iodine staining and pollen tube germination,which confirmed the reduced male gamete fertility.3.JMJ706 is involved in the regulation of photoperiodic response.We found that the jmj706 mutation significantly delayed heading date and increased plant height under short-day conditions,while these phenotypes were absent under long-day conditions.Examination of stem sections revealed that the increase in plant height was mainly due to an increase of cell numbers.Furthermore,to investigate the role of JMJ706 in the regulation of photoperiod flowering,we screened interacting proteins by yeast two-hybrid method and identified a circadian clock component Os Hd17/Os ELF3.1 that interacted with JMJ706.4.JMJ706 and JMJ707 are homologous genes.By analyzing the expression patterns of JMJ706 and JMJ707,we found that both JMJ706 and JMJ707 were constitutive expression,and their expression patterns were very similar.Furthermore,subcellular localization analysis showed that,like JMJ706,JMJ707 was localized in the nucleus.The predicted enzymatic active site is conserved in JMJ706 and JMJ707.Homology modeling analysis indicated that their structures are highly similar.In view of the above findings,we speculate that JMJ706 and JMJ707 may have similar functions in rice.5.JMJ706 and JMJ707 have functional redundancy in floral organ development.Based on the high homology between JMJ706 and JMJ707,the jmj706 jmj707 double mutant was constructed using CRISPR-Cas9 technology.The jmj706 jmj707 double mutant showed defects mainly in stigma,spikelet glume development and pollen fertility,and the phenotype of floral organ development in double mutant plants was more severe than the jmj706 single mutant.This suggests that JMJ707 may also be involved in the development of rice floral organs,and has genetically functional redundancy with JMJ706.In conclusion,this study uncovered more details of JMJ706 function in floral organ development,fertility,photoperiod flowering,plant height and other developmental aspects,and its functional relationship with the homologous gene JMJ707.