3^rd International Conference on Plant Science & Physiology May 21-22, 2018 Osaka, Japan

Biography:

Abstract:

Pathogenic Gram-negative bacteria interact with their eukaryotic hosts by deploying the type III translocon. The translocon compositions, the number and biochemical characteristics of type III translocators in animal-pathogenic bacteria have been well elucidated, but not for plant-pathogenic bacteria. With extensive studies on biological functions of the Hpa1 protein secreted by the type III secretion system in Xanthomonas oryzae pv. oryzae (Xoo), we showed that Hpa1 is a type III translocator based on measurements of two proteins categorized as transcription activator-like (TAL) effector. Hpa1 was functionally associated with the TAL effector PthXo1 or AvrXa10 by genetic analysis of the wild-type Xoo strain and related mutants or recombinant strains. Inoculation experiments suggested that Hpa1 is required not only for the virulent role of PthXo1 in the susceptible rice variety Nipponbare, but also for the avirulent function of AvrXa10 on the resistant rice variety IRBB10. Hpa1 is unrelated to the secretion of PthXo1 and AvrXa10 out of bacterial cells. However, Hpa1 is critical for both TAL effectors to be translocated from bacterial cells into the cytosol of rice cells based on replicate experiments performed on the susceptible and resistant varieties, respectively. Hpa1-mediated translocation of PthXo1 is coincident with induced expression of rice SWEET11 gene regulatory target of PthXo1, resulting in the occurrence of the bacterial blight disease in the susceptible rice variety. By contrast, the immune hypersensitive response is induced in agreement with induced expression of rice Xa10 gene, which is the target of AvrXa10, only when AvrXa10 is translocated from bacteria into cells of the resistant rice variety. All the virulent or avirulent performances of the TAL effectors are nullified by directed mutation that removes the α-helix motif from the Hpa1 sequence. The effect of the directed mutation suggests that Hpa1 depends on its α-helical motif to fulfil the translocator function.

 

Biography:

Abstract:

Recently we elucidated that tobacco TTG2 cooperates with ARF8 to regulate the vegetative growth and seed production. Here we show that TTG2 and ARF8 control flower colorization by regulating the expression of ANS and DRF genes, which function in anthocyanin biosynthesis. Genetic modifications that substantially altered expression levels of the TTG2 gene and production quantities of the TTG2 protein were correlated with flower development and colorization. Degrees of flower colorization were increased by TTG2 overexpression but decreased by TTG2 silencing in coincidence with high and low concentrations of anthocyanins in flowers. Of five genes involved in the anthocyanin biosynthesis pathway, only ANS and DRF were TTG2-regulated and displayed enhancement and diminution of expression with TTG2 overexpression and silencing, respectively. The floral expression of ANS and DRF also needed a functional ARF8 gene as ANS and DRF expression was attenuated by ARF8 silencing, which concomitantly diminished the role of TTG2 in anthocyanin production. While ARF8 required TTG2 to be expressed by itself and to regulate ANS and DRF expression, the concurrent presence of normally functional TTG2 and ARF8 was critical for the floral production of anthocyanins and for flower colorization as well. Our data suggest that TTG2 cooperates with ARF8 to control degrees of flower colorization by regulating the expression of ANS and DRF, which are involved in the anthocyanin biosynthesis pathway. ARF8 depends on TTG2 to regulate the floral expression of ANS and DRF with the positive effects on anthocyanin production and flower colorization.