AtERF14, a member of the ERF family of transcription factors, plays a nonredundant role in plant defense

Abstract

We had previously shown that several transcription factors of the ethylene (ET) response factor (ERF) family were induced with different but overlapping kinetics following challenge of Arabidopsis (Arabidopsis thaliana) with Pseudomonas syringae pv tomato DC3000 (avrRpt2). One of these genes, a transcriptional activator, AtERF14, was induced at the same time as ERF-target genes (ChiB, basic chitinase). To unravel the potential function of AtERF14 in regulating the plant defense response, we have analyzed gain- and loss-of-function mutants. We show here that AtERF14 has a prominent role in the plant defense response, since overexpression of AtERF14 had dramatic effects on both plant phenotype and defense gene expression and AtERF14 loss-of-function mutants showed impaired induction of defense genes following exogenous ET treatment and increased susceptibility to Fusarium oxysporum. Moreover, the expression of other ERF genes involved in defense and ET/jasmonic acid responses, such as ERF1 and AtERF2, depends on AtERF14 expression. A number of ERFs have been shown to function in the defense response through overexpression. However, the effect of loss of AtERF14 function on defense gene expression, pathogen resistance, and regulation of the expression of other ERF genes is unique thus far. These results suggest a unique role for AtERF14 in regulating the plant defense response.

Figure 1.

Phenotype of two representative lines overexpressing AtERF14 in the Col background (left) compared to wild-type Col-0 (right). Top, Plants grown for 3 weeks on MS containing kanamycin for ox-AtERF14 or MS for wild type; bottom, plants at 7 weeks after germination. [See online article for color version of this figure.]

Figure 2.

Examination of cell number and cell size in AtERF14-overexpressing plants and wild type. The number of palisade mesophyll cells per 1-mm region along transverse sections of leaves is shown for wild type and ox-AtERF14 lines. “Wild type similar age” are leaves of a similar age to those selected for ox-AtERF14 but are larger in size. “Wild type similar size” are younger leaves than those selected for ox-AtERF14 but are of a similar size. The average and se of 10 replicate regions from two leaves are presented.

Figure 3.

Expression of defense-associated genes in AtERF14-overexpressing lines. Gene expression is presented relative to average wild-type levels. The average and se of two technical replicates are presented.

Figure 4.

Mutant lines containing T-DNA insertions in the AtERF14 gene. A, Schematic diagram showing the position of T-DNA insertions in the AtERF14 gene. The AtERF14 open reading frame does not contain any introns. B to E, Defense gene expression in wild type, Δaterf14-1, and Δaterf14-2 lines with and without 24 h of ET treatment. Gene expression is presented relative to untreated wild-type levels. Average and se of two biological replicates are presented.

Figure 5.

ERF gene expression in wild type, Δaterf14-1, and Δaterf14-2 with and without 24 h of ET treatment. Gene expression is presented relative to untreated wild-type levels. Average and se of two biological replicates are presented.

Figure 6.

Defense gene expression in wild type, Δaterf14-1, and Δaterf14-2 lines with and without 24 h of MeJA (MJ) treatment (A and B) or SA treatment (C and D). Gene expression is presented relative to untreated wild-type levels. The average and se of five biological replicates are presented.

Figure 7.

Response of wild type, Δaterf14-1, and Δaterf14-2 to inoculation with R. solani. Dry root weight of plants inoculated with R. solani is expressed as the percentage of dry root weight of control, noninoculated plants.

Figure 8.

Response of wild type, Δaterf14-1, and Δaterf14-2 to inoculation with F. oxysporum. A, The percentage of survival of plants inoculated with F. oxysporum. B, The dry root weight of F. oxysporum-inoculated plants expressed as the percentage of control, noninoculated plants. Points represent the average of five plants from each pot. Levels not connected by the same letter are significantly different (P < 0.05) according to Tukey-Kramer honestly significant difference test.