Creation of a rectangle with texture fails - opengl

Question

I want to draw a simple rectangle in OpenGL 3.0 with a texture on it. As starting point I use the example from https://learnopengl.com/code_viewer_gh.php?code=src/1.getting_started/4.2.textures_combined/textures_combined.cpp but with some modifications:
all done for GLSL 1.3
no colours in vertex-array
only one texture instead of two overlapping ones
So I modified this code as follows. The vertex shader:
#version 130
in vec3 aPos;
in vec2 aTexCoord;
out vec2 TexCoord;
uniform mat4 inputTransform;
void main()
{
TexCoord=vec2(aTexCoord.x, aTexCoord.y);
gl_Position = inputTransform * vec4(aPos.x, aPos.y, aPos.z, 1.0);
}
The fragment shader:
#version 130
out vec4 FragColor;
in vec2 TexCoord;
uniform sampler2D texture1;
void main()
{
FragColor=texture(texture1, TexCoord);
}
-> both of them compile without errors
My vertex coordinates are arranged in one array making use of x,y,z,u,v:
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
glEnableVertexAttribArray(0);
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
glEnableVertexAttribArray(1);
The GL_TRIANGLE_STRIP-based rectangle (without UV-coordinates and without the texture-stuff) works well and has the correct size but as soon as I apply the texture coordinates and function calls to it, nothing more than a very tiny triangle is drawn.
So I'd guess something goes wrong with the coordinates in my vertex array. But...what exactly could be wrong here?
Update: my VBO/VAO setup (simplified, so error handling code is not shown):
gl3Element->shaderProgram=glCreateProgram();
glAttachShader(gl3Element->shaderProgram, m_gl3TexVertexShader);
glAttachShader(gl3Element->shaderProgram,m_gl3TexFragmentShader);
glLinkProgram(gl3Element->shaderProgram);
glDeleteShader(m_gl3TexFragmentShader);
glDeleteShader(m_gl3DynColourFragmentShader);
glUseProgram(gl3Element->shaderProgram);
glGenVertexArrays(1, &gl3Element->VAO);
glGenBuffers(1, &gl3Element->VBO);
...and the texture-specific stuff to sue them:
glGenTextures(1, &imgEntity->m_glTexture);
glBindTexture(GL_TEXTURE_2D, imgEntity->m_glTexture);
glTexImage2D(GL_TEXTURE_2D,0,GL_RGBA,transImage->GetWidth(),transImage->GetHeight(),0,GL_RGB,GL_UNSIGNED_BYTE,transImage->GetData());
glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
glGenerateMipmap(GL_TEXTURE_2D);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, imgEntity->m_glTexture);