Molecular Mechanisms Of NF-YB2 And NF-YB3 Balancing Flowering Time And Disease Resistance In Plants

Plants have developed a series of relatively perfect immune systems to resist the infection of pathogenic microorganisms and pests in the process of adapting to the external environment.The endogenous hormones Salicylic Acid,SA and Jasmonate Acid,JA are essential for plant immunity.They can induce the broad-spectrum defense of plants by activating signal transduction.Nuclear Factor-Y,(NF-Y,consisting of three subunits: NF-YA,NF-YB and NF-YC,are ubiquitous in higher eukaryotes.It is known that NF-YB2 and NF-YB3(later referred as YB2 and YB3)are critical for stress response,and they play redundant roles in flowering regulation.CO(CONSTANS)is a major flowering regulator,YB2 and YB3 can promote plant flowering by facilitating CO binding to FT promoter,or by recruiting H3K27 demethyltransferase REF6 to reduce the H3K27me3 level in SOC1 promoter and then promote the transcription of SOC1,thus positively regulating plant flowering time.In order to explore whether and how YB2 and YB3 coordinate plant immunity and flowering,we studied the transcription and protein levels of YB2 and YB3,the main results are as follows:yb2 and yb3 mutants are more resistant to Pst DC3000,meanwhile,JA and disease resistance associated genes were differentially expressed in yb2 yb3 double mutant.JAZ proteins are important repressors in JA signaling pathway,able to inhibit the transcription of MYC2.We found that YB2 interacts with most JAZ proteins,but fewer with YB3.In addition,the transcriptional activation of MYC2 by pathogen or Me JA treatment in yb2 and yb3 mutants are both surpressed,which indicated that YB2 and YB3 can promote the transcription of MYC2.Besides,the sensitivity of singal mutant yb2,yb3 and double mutant yb2 yb3 to methyl jasmonate decreased as well.However,the molecular mechanisms of YB2 and YB3 in MYC2 transcriptional regulation are not identical.After co-expression of YB2 with JAZs and MYC2:pro-LUC in Nicotiana benthamiana,we found that the transcriptional inhibition of MYC2 by JAZs was released by YB2.But YB3 did not involve in the transcription inhibition of MYC2 via JAZ proteins.Moreover,the expression of downstream genes regulated by YB2 and YB3 were also distinct.The expression levels of ANAC019 and ICS1 changed in yb2 mutant,but in yb3 the transcription of VSP2 decreased,and altered the insect resistance of plants.Previous studies have shown that COI1 is associated with the regulation of JAZ-TOE1-FT pathway,thereby affecting plant flowering time.COI1 is the key protein of JA signal pathway,after recognizing JA signaling,COI1 can recruit JAZ protein to ubiquitinate and degrade JAZ proteins through 26 S proteasome.JAZ proteins are able to inhibit the transcription of TOE1/2 and attenuate the transcriptional inhibition of FT gene by TOE1/2,then promote plant flowering.In order to reveal the molecular mechanism of YB2 and YB3 coordinating JA signaling pathway and affecting flowering,we hybridized coi1-2 with yb2 yb3 and compared the flowering time of different genotypes.It was found that the early flowering phenotype of coi1-2 and the expression of FT rescued in yb2 yb3,and the expression levels of YB2 and YB3 in coi1-2 mutant were significantly up-regulated.We also found that the activation or inhibition of JA signaling pathway did not affect the accumulation of YB2 and YB3 in plants.It suggests that the early flowering of coi1-2may promote the expression of FT and SOC1 by inhibiting the transcription of YB2 and YB3,and this process is independent in JA signaling pathway.In conclusion,we explored the role of nuclear factor YB2 and YB3 in JA mediated plant immune response,and studied the molecular mechanisms of YB2 and YB3 in JA signal response.We also revealed that COI1 involved in plant flowering regulation by reducing the transcription level of YB2 and YB3 in a way independent of JA signaling pathway.We preliminary analysed how YB2 and YB3 coordinated regulate plant immunity and flowering time.