Enhanced resistance against Thielaviopsis basicola in transgenic cotton plants expressing Arabidopsis NPR1 gene

Abstract

Black root rot, caused by Thielaviopsis basicola, is an important disease in several crops including cotton. We studied the response of Arabidopsis NPR1 (AtNPR1)-expressing cotton lines, previously shown to be highly resistant to a diverse set of pathogens, to a challenge from T. basicola. In four different experiments, we found significant degree of tolerance in the transgenic lines to black root rot. Although transformants showed the typical root discoloration symptoms similar to the wild-type control plants following infection, their roots tended to recover faster and resumed normal growth. Better performance of transgenic plants is reflected by the fact that they have significantly higher shoot and root mass, longer shoot length, and greater number of boll-set. Transcriptional analysis of the defense response showed that the roots of AtNPR1-overexpressing transgenic plants exhibited stronger and faster induction of most of these defense-related genes, particularly PR1, thaumatin, glucanase, LOX1, and chitinase. The results obtained in this investigation provide further support for a broad-spectrum nature of the resistance conferred by overexpression of AtNPR1 gene in cotton.

Response of AtNPR1-expressing cotton plants to Fusarium oxysporum f. sp. vasinfectum isolates

“…Also, note that in the absence of a biotic challenge, the basal level activities of most of these genes are not elevated in the AtNPR1 transformants. Thus, in this regard we have further confirmed the results of our earlier studies (Parkhi et al 2010a;Kumar et al 2013). Based on the promising results against a broad spectrum of pathogens (Parkhi et al 2010a;Kumar et al 2013), we wondered if the tolerance would extend to other Fov isolates and especially, those known to be more virulent compared to Fov11.…”

“…In our earlier investigations with AtNPR1 expressing cotton lines, we found that the transformants exhibited significant tolerance to V. dahliae (non-defoliating isolates TS2 and EZ2) Fov11, R. solani, T. basicola, A. alternata, and also reniform nematodes (Parkhi et al 2010a;Kumar et al 2013). In this study we examined the disease progression using GFP-expressing Fov11 culture, which provided us with a reliable assay to examine the spread of the disease.…”

“…Transgenic cotton plants (Coker 312) expressing an AtNPR1 gene under the control of CaMV 35S promoter have shown resistance to multiple fungal pathogens, including Fov11 (Parkhi et al 2010a;Kumar et al 2013). T4 generation plants of a transgenic line, 68L-19, were used in the current investigation.…”

“…These primers were used to amplify target gene sequences from the cDNA prepared from infected root RNA. PCR products were purified, labeled with P 32 -dCTP, and used as probes in Northern hybridization as previously describe by Kumar et al (2013). qRT-PCR analysis was performed on hypocotyl samples to study the expression of GhPR1, GhLOX1, Ghchitinase and GhGlucanse genes.…”

“…A recent study showed enhanced resistance against Huanglongbing disease in citrus plants expressing the AtNPR1 gene (Dutt et al 2015). In our earlier investigations, we found that expression of AtNPR1 in cotton conferred protection against two necrotrophic fungal pathogens, R. solani, (a cause of seedling damping-off) and A. alternata (a cause of foliar disease), two wilt diseases, Fusarium wilt caused by Fov and Verticillium wilt caused by nondefoliating pathotype of Verticillium dahliae, black root rot caused by T. basicola, and reniform nematodes (Parkhi et al 2010a;Parkhi et al 2010b;Kumar et al 2013). …”