TheArabidopsisMyb transcription factor MTF1 is a unidirectional regulator of susceptibility toAgrobacterium

Abstract

We recently described the Arabidopsis Myb transcription factor MTF1 that negatively regulates plant susceptibility to Agrobacteriummediated transformation. Roots of mtf1 mutant plants show increased susceptibility to several Agrobacterium strains, and complementing the mutants with a MTF1 cDNA decreases transformation susceptibility to wild-type levels. Here, we show that overexpression of MTF1 in a wild-type Arabidopsis background does not result in altered transformation susceptibility. However, MTF1 overexpressing plants show increased root length and larger and darker leaves, indicating that MTF1 plays a role in plant growth and development. MTF1 decreases Arabidopsis root susceptibility specifically to Agrobacterium but plant responses to the pathogens Alternaria brassicicola or Pseudomonas syringae pv Tomato were not altered. However, the homozygous MTF1 mutant mtf1-4 is resistant to Botrytis cinerea strain BO5-10 and is regulated through the ethylene signaling pathway mediated by upregulation of the AP2/ERF transcription factor ORA59.Over the past ~40 years, numerous studies have been conducted elucidating the molecular and genetic mechanisms of Agrobacterium-mediated plant transformation. However, only recently has the involvement of plant genes in the transformation process been investigated. Although specific plant genes mediate various steps of transformation, no gene that regulates the extent of transformation susceptibility had previously been described.We recently identified an Arabidopsis Myb transcription factor, MTF1, that plays a role in regulating Agrobacteriummediated transformation susceptibility. 1 mtf1 mutants show increased susceptibility to several Agrobacterium strains. In addition, decreasing MTF1 expression, using an RNAi approach, increases transformation susceptibility of a recalcitrant Arabidopsis ecotype. Ectopic overexpression of a MTF1 cDNA in the mtf1-4 homozygous mutant resulted in decreased transformation susceptibility of the resultant transgenic lines. Because decreased expression of MTF1 results in increased transformation susceptibility, we hypothesized that MTF1 is a "bidirectional regulator" such that decreased MTF1 expression would increase plant transformation susceptibility, whereas overexpression of MTF1 would decrease susceptibility to Agrobacterium-mediated transformation.We generated 5 MTF1 cDNA overexpression lines in wild-type Arabidopsis (ecotype Col-7) that showed a 9-to 43-fold increase in MTF1 transcript levels, as assessed by quantitative real-time reverse transcription PCR (Fig. 1A). We tested the transformation susceptibility of the overexpression line 4 (MTF-4) that had the highest MTF1 transcript level. There was no alteration in the transformation susceptibility of MTF-4 compared with that of wild-type plantsThe Arabidopsis Myb transcription factor MTF1 is a unidirectional regulator of susceptibility to Agrobacterium

Advancing Crop Transformation in the Era of Genome Editing

“…For example, altered production of the plant proteins has increased host susceptibility to transformation (Gelvin, 2010). In particular, an Arabidopsis MYB transcription factor (MTF) appears to function as a global negative regulator of transformation susceptibility; downregulation of MTF can increase Arabidopsis transformation 15-fold (Sardesai et al, 2013(Sardesai et al, , 2014. Conversely, some host proteins are activated or produced in response to Agrobacterium.…”