Abstract:

Citrus canker,caused by is a bacterial disease,which severely influence citrus industry,and its pathogenicity is significantly enhanced under higher temperature and humidity environmental condition. HSP20 genes are abundant and highly conserved in higher plants,they play vital defense roles when plants are under biotic or abiotic stress. In order to investigate the role of HSP20 genes in response to Xanthomonas citri subsp. citri infection,the genes of HSP20 family in Citrus sinensis were identified. The analysis of biological information showed that there are 42 members,which can be divided into 11 subfamilies,they encode 135-373 aa and are distributed on nine chromosomes,their protein molecular weight are from 15.17 to 41.71 kD,isoelectric point are from 4.53 to 10.07,almost 92.9% of them not contain any intron or only one,and each subfamily share highly similar structures and conserved motifs,their promoter also has cis-acting elements response to hormones or stress. In order to access the role of CsHSP20 in response to Xcc and abiotic stress in resistant germplasm Citron C-05 with susceptible sweet orange,we have injected Xcc into the leaves of Citron C-05 and conducted a series of heat stress with small Citron C-05 plants. The relative expression levels of CsHSP20 have been screened by qRT-PCR,the results showed that HSP17.9,HSP23.3,HSP18.5 and HSP18.0 were up-regulated in both Xcc and heat stress,but their relative expression level in Citron C-05 is notably different from that of sweet orange under Xcc infection,especially HSP23.3. Interestingly,the induced expression patterns are consistent with the result of the transcriptomic analysis infected by Xcc. Then,these genes have been transiently overexpressed in sweet orange leaves,and Xcc quantitative analysis of Citron C-05 HSP23.3 showed that Xcc reproduction was inhibited.

Key words: citrus, citron, HSP20, canker, expression analysis