FIGURE 4.

Salicylic acid (SA) is not essential for the GhSSI2‐conferred activation of defence phenotypes. (a) The transcript levels of SA signal transduction pathway genes. The values are the mean ± SE for three biological replicates (**p < 0.01, Student's t test). (b) Morphological features of double‐gene‐silenced plants by virus‐induced gene silencing (VIGS). Co‐suppressed plants had similar phenotypes to TRV:GhSSI2 plants. TRV:SP (TRV:GhSSI2 & Gh PAL) and TRV:SI (TRV:GhSSI2 & Gh ICS1) represented cosuppressed plants with different gene combinations. Photographs were obtained 2 weeks after VIGS. (c) Measurements of the SA and SA glucoside (SAG) in the cosuppressed cotton leaves. TRV:SP and TRV:SI had lower SA levels than the TRV:GhSSI2 plants. The values are the mean ± SE for three biological replicates (* p< 0.05, **p < 0.01, Student's t test). (d, e) The content of H₂O₂ was elevated in the cosuppressed cotton leaves. (f) Expression patterns of PR genes in the TRV:SP and TRV:SI plants