Host mechanisms for resistance to TAL effectors: Thinking outside the UPT box

• This is a commentary on non-transcriptional plant responses to TAL effectors.
• There are many ways plants might evolve to resist the effects of TAL effectors.
• Such mechanisms are little-studied but could impact effector effectiveness.

Transcriptional activator like (TAL) effectors are important virulence factors of several plant pathogenic species of Xanthomonas. Members of this secreted protein family may activate transcription of; susceptibility factors, favoring disease, or resistance genes, triggering immunity. Accordingly, most research in this area has focused on the responses of a few model varieties of plants to the transcriptional activities of TAL effectors. However, a few studies suggest that plants may have evolved a diversity of additional responses to TAL effectors that are not well understood. These could include resistance to the effects of the TAL-activated susceptibility factors such as carbohydrate transporters, genomic multiplication of off-target effector binding sites, direct receptor recognition of the conserved TAL effector structure, or mutation of the host machinery required for TAL effector function. A better understanding of the diversity of plant responses to TAL effectors will be important for harnessing the potential of these proteins for agricultural applications.