Biochemical and molecular characterization of non-host resistance keys in food crops

Abstract

Generally, under normal conditions plants are resistant to many of the incompatible pathogens (viral, fungal and bacterial), and this is named "non-host resistance phenomenon". To understand this phenomenon, different types of food crops (faba bean, squash, barley and wheat) were inoculated with compatible and incompatible pathogens. Strong resistance symptoms were observed in the non-host/incompatible pathogen combinations as compared with host/compatible pathogen combinations, which showed severe infection (susceptibility). Reactive oxygen species (ROS) mostly hydrogen peroxide and superoxide were significantly increased early 24 and 48 h after inoculation (hai) in the non-host plants comparing to the host. Antioxidant enzymes activity (catalase, polyphenol oxidase and peroxidase) were not increased at the same early time 24, 48 hai in the non-host resistant and host resistant plants, however, it increased later at 72 and 168 hai. Electrolyte leakage decreased significantly in non-host resistant and host resistant/pathogen combinations. Catalase and peroxidase genes were significantly expressed in non-host resistant and in host resistant plants as compared to the host susceptible one, which did not show expression using RT-PCR technique. Furthermore, Yr5, Yr18 and Yr26 resistant genes were identified positively using PCR in all treatments either host susceptible or non-host resistant plants in which prove that no clear role of these resistant genes in resistance. Early accumulation of ROS could have a dual roles, first role is preventing the growth or killing the pathogens early in the non-host, second, stimulating the gene appearance of related genes in addition the activition of antioxidant enzymes later on which thereby, neutralize the harmful effect of ROS and consequently suppressing disease symptoms. The new finding from this study supporting the plant breeders with new source of resistance to develop new resistant cultivars and/or stop the breakdown of resistance in resistant cultivars.

Keywords: Antioxidants; Gene expression; Non-host resistance; Reactive oxygen species.

Fig. 1

Disease symptoms of host (H) and non-host (NH)/pathogen combinations 7 days after inoculation (dai) in squash, faba bean, wheat and barley plants. Host squash: inoculated leaves with Papaya ring spot virus (PRSV). Host faba bean: inoculated leaves with B. fabae (Bf). Non-host Squash: inoculated leaves with P. striiformis f.sp. tritici (Pst). Non-host faba bean: inoculated leaves with PRSV. Host wheat: inoculated leaves with B. graminis f. sp. tritic (Bgt) and Pst. Non-host wheat: inoculated leaves with Blumeria graminis f. sp. hordei (Bgh) and Uromyces fabae (Uf). Host Barley: inoculated leaves with Bgh and Pyenophora teres (Pt). Non-host Barley: inoculated leaves with Bgt and (PRSV).

Fig. 2

Purple discoloration of O₂^•−) (upper row) and brown discoloration H₂O₂ (lower row) of host (H) and non-host (NH)/pathogen combinations 24 h after inoculation (hai) in Squash, faba bean, Wheat and Barley plants. Host Squash: leaves inoculated with Papaya ring spot virus (PRSV). Host faba bean: leaves inoculated with Botrytis fabae (Bf). Non-host Squash: leaves inoculated with Puccinia striiformis f.sp. tritici (Pst). Non-host faba bean: leaves inoculated with PRSV. Host Wheat: leaves inoculated with Blumeria graminis f. sp. tritic (Bgt) and Pst. Non-host Wheat: leaves inoculated with Blumeria graminis f. sp. hordei (Bgh) and Uromyces fabae (Uf). Host Barley: leaves inoculated with Bgh and Pyenophora teres (Pt). Non-host Barley: leaves inoculated with Bgt and (PRSV).

Fig. 3

Antioxidant enzymes activity (CAT, POX and PPO) in host and non-host/pathogen combinations 24, 48, 72 and 168 h after inoculation (hai) in squash and faba bean plants. Host squash: leaves inoculated with Papaya ring spot virus (PRSV). Host faba bean: leaves inoculated with Botrytis fabae (Bf). Non-host squash: inoculated leaves with Puccinia striiformis f.sp. tritici (Pst). Non-host faba bean: leaves inoculated with PRSV.

Fig. 4

Antioxidant enzymes activity (CAT, POX and PPO) in host and non-host/pathogen combinations 24, 48, 72 and 168 h after inoculation (hai) in wheat and barley plants. Host wheat: inoculated leaves with Blumeria graminis f. sp. tritic (Bgt). Host barley: inoculated leaves with Blumeria graminis f. sp. hordei (Bgh). Non-host wheat: inoculated leaves with (Bgh). Non-host barley: inoculated leaves with (Bgt).

Fig. 5

Antioxidant enzymes activity (CAT, POX and PPO) in host and non-host/pathogen combinations 24, 48, 72 and 168 h (hai) after inoculation in wheat and barley plants. Host wheat: inoculated leaves with Puccinia striiformis f.sp. tritici (Pst). Host barley: inoculated leaves with Pyenophora teres (Pt). Non-host wheat: inoculated leaves with Uromyces fabae (Uf). Non-host barley: inoculated leaves with Papaya ring spot virus (PRSV).

Fig. 6

Electrolyte leakage of host and non- host /pathogen combinations 24, 48, 72, 168 h after inoculation (hai) in squash and faba bean plants. Host squash: inoculated leaves with Papaya ring spot virus (PRSV). Host faba bean: inoculated leaves with Botrytis fabae (Bf). Non-host squash: inoculated leaves with Puccinia striiformis f.sp. tritici (Pst). Non-host faba bean: inoculated leaves with PRSV.

Fig. 7

Electrolyte leakage of host and non- host /pathogen combinations 24, 48, 72, 168 h (hai) after inoculation in wheat and barley plants. Host wheat: inoculated leaves with Blumeria graminis f. sp. tritic (Bgt). Host barley: inoculated leaves with Blumeria graminis f. sp. hordei (Bgh). Non-host wheat: inoculated leaves with (Bgh). Non-host barley: inoculated leaves with (Bgt).

Fig. 8

Electrolyte leakage of host and non- host /pathogen combinations 24, 48, 72, 168 h after inoculation (hai) in wheat and barley plants. Host Wheat: leaves inoculated with Puccinia striiformis f.sp. tritici (Pst). Host Barley: leaves inoculated with Pyenophora teres (Pt). Non-host Wheat: inoculated leaves with Uromyces fabae. Non-host Barley: inoculated leaves with Papaya ring spot virus (PRSV).

Fig. 9

Amplification results of PCR products using Yr5 marker (478 bp); Yr18 marker (517 bp); and Yr26 marker (7451 bp) in host and nonhost plants. L: ladder; HR: host-resistance; M: mock; HS: host-susceptabile; NH: non-host; P: positive control of the gene; N: negative control.

Fig. 10

RT-PCR analysis of antioxidants genes Expression. (A) Expression of peroxidase (POX); (B) Expression of catalase (CAT); (C) Expression of Actin gene using as a control in host and non-host plants, 24 h after inoculation (hai).