Wg. Zhu et al., AVRXA10 CONTAINS AN ACIDIC TRANSCRIPTIONAL ACTIVATION DOMAIN IN THE FUNCTIONALLY CONSERVED C-TERMINUS, Molecular plant-microbe interactions, 11(8), 1998, pp. 824-832
The avrXa10 gene of Xanthomonas oryzae pv, oryzae, the causal agent of
bacterial blight of rice, is a member of the avrBs3 avirulence gene f
amily and directs the elicitation of resistance in a gene-for-gene man
ner on rice lines carrying the resistance gene Xa10. The carboxyl (C)
terminus of AvrXa10 has a previously undescribed domain that is struct
urally similar to the acidic activation domain of many eukaryotic tran
scription factors in addition to three nuclear localization signal (NL
S) sequences. Removal of the C-terminal 38 codons containing the putat
ive activation domain, but retaining the NLS sequences, was concomitan
t with the loss of avirulence activity. The C-terminal coding regions
of avrBs3 and avrXa7 can be replaced by the corresponding region of av
rXa10, and the genes retained specificity for the resistance genes Bs3
in pepper and Xa7 in rice, respectively. The avrBs3 and avrXa7 avirul
ence activities of the hybrid genes were also lost upon removal of the
terminal 38 codons, When fused to the coding sequence of the Ga14 DNA
binding domain, AvrXa10 activated transcription in yeast and Arabidop
sis thaliana. Removal of the carboxyl region severely reduced transcri
ptional activation. AvrXa10 would have to be localized to the host cel
l nucleus to function autonomously in transcriptional activation. Cons
istent with this requirement, mutations in all three NLS sequences of
avrXa10 caused a loss in avirulence activity, The findings demonstrate
the requirement of the C terminus for AvrXa10 function and the potent
ial for the members of this family of avirulence gene products to ente
r the host nucleus and alter host transcription.