Five phylogenetically close rice SWEET genes confer TAL effector‐mediated susceptibility to Xanthomonas oryzae pv. oryzae

Abstract

Summary: Bacterial plant‐pathogenic Xanthomonas strains translocate transcription activator‐like (TAL) effectors into plant cells to function as specific transcription factors. Only a few plant target genes of TAL effectors have been identified, so far. Three plant SWEET genes encoding putative sugar transporters are known to be induced by TAL effectors from rice‐pathogenic Xanthomonas oryzae pv. oryzae (Xoo). We predict and validate that expression of Os SWEET 14 is induced by a novel TAL effector, Tal5, from an African Xoo strain. Artificial TAL effectors (Art TAL s) were constructed to individually target 20 SWEET orthologs in rice. They were used as designer virulence factors to study which rice SWEET genes can support Xoo virulence. The Tal5 target box differs from those of the already known TAL effectors TalC, AvrXa7 and PthXo3, which also induce expression of Os SWEET 14, suggesting evolutionary convergence on key targets. Art TAL s efficiently complemented an Xoo talC mutant, demonstrating that specific induction of Os SWEET 14 is the key target of TalC. Art TAL s that specifically target individual members of the rice SWEET family revealed three known and two novel SWEET genes to support bacterial virulence. Our results demonstrate that five phylogenetically close SWEET proteins, which presumably act as sucrose transporters, can support Xoo virulence.