Bacterial blight is one of the most destructive diseases of rice worldwide.
It is caused by Xanthomonas oryzae pv. oryzae (Xoo), which recruits
transcription activator-like effectors (TALEs) to promote the expression of
OsSWEET genes which are vital in sugar transport and disease susceptibility.
To develop broad-spectrum bacterial blight resistance, scientists from
Shanghai Jiao Tong University in China used CRISPR-Cas9 to break the
TALE-binding elements of the susceptibility genes, OsSWEET11 and OSSWEET14
in rice.



The resulting rice line MS14K showed broad-spectrum resistance to most Xoo
strains, which may imply that the compatible strains may have new TALEs.
They found two types of PthXo2-like TALEs that function as major virulence
factors in the compatible Xoo strains. Xoo encodes 5 types of PthXo2-like
effectors. Since PthXo2/PthXo2.1 target OsSWEET13 for transcriptional
activation, the genomes of 3,000 rice varieties were analyzed for variations
of TALE-binding elements (EBE). The two PthXo2-like TALEs were found to bind
slightly different EBE sequences and activated their expression. Then
CRISPR-Cas9 was used to produce insertions and deletions in the EBE of
OsSWEET13 promoter in the mutant MS14K. This led to the development of new
germplasm with tree edited OsSWEET EBEs and broad-spectrum resistance
against Xoo.

The research shows how to develop broad-spectrum resistance through the loss
of effector-triggered susceptibility in plants.

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