Growth and development of plants are dependent on sunlight. Consequently, plants have evolved a sophisticated array of photoreceptor systems to control their growth. Phototropins are plant photoreceptors that are specifically receptive to UV-A/blue light (320–500 nm) (UV-A is one of the types of ultraviolet radiation produced by the Sun, in the wavelength range 320–400 nm; blue light has an approximate wavelength range of 400–500 nm). They control a range of responses concerned with optimizing the photosynthetic efficiency of plants, thereby promoting their growth, particularly under weak light conditions.