A single plant resistance gene promoter engineered to recognize multiple TAL effectors from disparate pathogens

Abstract

Plant pathogenic bacteria of the genus Xanthomonas inject transcription-activator like (TAL) effector proteins that manipulate the hosts' transcriptome to promote disease. However, in some cases plants take advantage of this mechanism to trigger defense responses. For example, transcription of the pepper Bs3 and rice Xa27 resistance (R) genes are specifically activated by the respective TAL effectors AvrBs3 from Xanthomonas campestris pv. vesicatoria (Xcv), and AvrXa27 from X. oryzae pv. oryzae (Xoo). Recognition of AvrBs3 was shown to be mediated by interaction with the corresponding UPT (UPregulated by TAL effectors) box UPT AvrBs3 present in the promoter R gene Bs3 from the dicot pepper. In contrast, it was not known how the Xoo TAL effector AvrXa27 transcriptionally activates the matching R gene Xa27 from the monocot rice. Here we identified a 16-bp UPT AvrXa27 box present in the rice Xa27 promoter that when transferred into the Bs3 promoter confers AvrXa27-dependent inducibility. We demonstrate that polymorphisms between the UPT AvrXa27 box of the AvrXa27-inducible Xa27 promoter and the corresponding region of the noninducible xa27 promoter account for their distinct inducibility and affinity, with respect to AvrXa27. Moreover, we demonstrate that three functionally distinct UPT boxes targeted by separate TAL effectors retain their function and specificity when combined into one promoter. Given that many economically important xanthomonads deliver multiple TAL effectors, the engineering of R genes capable of recognizing multiple TAL effectors provides a potential approach for engineering broad spectrum and durable disease resistance.AvrBs3 ͉ AvrXa27 ͉ transcription-activator like effector proteins ͉ Xanthomonas

Lateral organ boundaries 1 is a disease susceptibility gene for citrus bacterial canker disease

“…By combining the natural EBEs of multiple TAL effectors from three distinct R genes or adding artificial EBEs of corresponding TAL effectors into one complex R gene promoter, the engineered R gene was induced by these effectors and conferred broader spectrum disease resistance (46,47). Although no major R genes have yet been described in citrus, the well-characterized avr gene AvrGf1 may reflect the presence of a potential R gene in grapefruit and sweet orange (3).…”

Structural basis of the TAL effector–DNA interaction

“…TALEs can be applied to transcription control as demonstrated in plants (Boch et al , 2009 ;Romer et al , 2009aRomer et al , ,b , 2010Morbitzer et al , 2010 ;Mahfouz et al , 2011 ;Weber et al , 2011 ; and in mammalian cell cultures (Geissler et al , 2011 ;Miller et al , 2011 ;Zhang et al , 2011 ;Bultmann et al , 2012 ). For engineered transcriptional control, TALE binding sites should be chosen in a way that will minimize off-target effects.…”

TAL effector-DNA specificity

“…Recently, it was shown that different TAL-boxes can be combined into one promoter to render this promoter responsive to several TAL effectors. 12 This demonstrated that the repeat number influences DNA binding. TAL effectors with a low number of repeats have less protein-DNA interactions than TAL effectors with many repeats and should thus have lower DNA affinity.…”

“…1A), 4 but does not efficiently recognize DNA sequences with two additional TAL-boxes can be inserted at different positions into a promoter and promoters can be generated that are induced by several TAL effectors. 12 This might be useful to generate plants carrying resistance genes under control of such promoters. These plants will be resistant to infection of bacteria carrying either one of the corresponding TAL effectors.…”