Metabolism Of Very-long Chain Fatty Acids Regulate Humidity-sensitive Genic Male Sterility

Environment-sensitive genic male sterility(EGMS)line is the key of twoline hybrid breeding and also an important material for studying plant environmental adaptability.Humidity-sensitive genic male sterility(HGMS)is a new type of EGMS in rice(Oryza sativa L.),and its phenotype is mainly caused by the developmental defects in the pollen wall.Pollen wall plays an important role in supporting the pollen grain structure,wrapping the contents,resisting the harsh environment and so on.In our previous study,a humidity-sensitive male sterile(HGMS)mutant was found in the regenerated lines of rice Zhonghua 11(ZH11)in our laboratory.Through mapping and functional complementation,it was proved that the HGMS gene HMS1(HUMIDITYSENSITIVE GENIC MALE STERILITY 1)encodes a β-ketoacyl-Co A synthase,and its functional loss will lead to HGMS.Here,we explored in detail the functions of HMS1 and summarized the following outcomes.1)To study whether overexpression of HMS1 can enhance the drought tolerance of rice,we overexpressed HMS1(HOE)in ZH11.Interestingly,HOE showed two different phenotypes(HOE1 and HOE2).HOE1 showed the similar phenotype of HGMS as hms1,while HOE2 showed pollen abortion.The ultra-structure of the anthers which revealed that the bacula and tryphine contents were reduced in the HOE1 relative to ZH11,similar to that of hms1.The seed setting rate of HOE1 decreased due to the abnormal development of pollen wall under low humidity environment,but recovered in high humidity environment;while HOE2 was completely sterile because of the collapsing pollen in low humidity.The sexine and nexine of the microspore are loose,and the bacula and tryphine were not fully developed.The abnormal development of pollen exine of HOE2 may lead to the collapse of microspores during anther programmed dehydration stage(S11).2)Furthermore,the mechanism of HGMS regulated by HMS1 was studied.The direct interaction between HMS1 and HMS1I(HMS1-INTERACTING PROTEIN)was found by yeast two-hybrid,Bi FC(Bimolecular Fluorescence Complementation)and Co IP(Co-Immunoprecipitation)assay.The RT-PCR(Reverse transcription Polymerase Chain Reaction)results showed that HMS1 I was mainly expressed in young panicles but low in mature anthers,as similar to that of HMS1.3)The knockout mutant of HMS1I(HMS1ICas)showed a similar to hms1,but weaker HGMS phenotype.The seed setting rate of HMS1 ICas plant decreased slightly under low humidity condition,and recovered in high humidity condition.Furthermore,the ultra-structure of the anthers which revealed that the bacula and tryphine contents were reduced in the HMS1 ICas relative to ZH11,similar to that of hms1.The decrease in the contents of the very long chain fatty acid(VLCFAs)with > C24 were very similar in HMS1 ICas and the hms1 mutant,relative to the levels in ZH11.The VLCFAs(>C24)could be synthesized only when HMS1 and HMS1 I existed simutaneously in yeast elo3 mutant with VLCFAs synthesis deficiency >C24.Briefly,this study found the overexpression of HMS1 in rice could also affect the development of the pollen wall,which accelerates the susceptibility of the pollen grains in response to humidity condition.These results indicate that the moderate expression level of HMS1 is very important for rice pollen development,over-expression and under-expression of HMS1 will lead to HGMS.Additionally,the interaction between HMS1 and HMS1 I can regulate the development of pollen wall by employing the biosynthesis of C26 and C28 VLCFAs and their derivatives,and the knockout of HMS1 I in ZH11 displayed a novel HGMS.Our findings provide extensive details in understanding the regulatory mechanism of HGMS in rice and are beneficial to promote the application of hms1 in two-line hybrid rice breeding.