Fear is witnessed throughout the animal kingdom. Do plants experience fear as well?

This is absolutely the case. Plants have consciousness. There have been studies showing unequivocally that if a plant is threatened, as with a burning flame, it will recoil simply from the awareness of the intention to cause it harm, and, in fact, the plants will remember and begin to react emotionally, in a sense, when that same person revisits their environment in the future. They will be recognized as a potential perpetrator and the plant will have a discernable reaction in terms of electrophysiological energetic emanations that are discernable and measurable scientifically. There are many ways this is expressed simply beyond a conscious awareness, even though of a primitive sort. There can be quite elegant physiological responses and production of chemical substances to act as a repellant if predatory creatures are detected on the surface of the plant or in a nearby environment. There is an elegant defensive posture plants can take even to protect themselves against other plants through a kind of chemical warfare by producing chemical substances that are herbicides for other plant species but benign to the self. This is why some plants cannot be placed too close to others because they will die off if this is done—that is a good example of the biowarfare plants will mount against one another to survive in a competitive environment. In a sense, this is a fear response because it is the ability to detect a threat to the existence that is linked in intricate ways to gene expression patterns that will produce a physiological response mounted to act as a deterrent to the encroachment of another organism that poses a threat to existence. One can argue in what ways this differs from a conscious awareness that would be true for a human being, but humans as well have subliminal fear detection mechanisms that occur deep within the subconscious and cue off of non-local consciousness going out and assessing the threat level of people and things in the environment, and giving feedback to the deep subconscious below conscious awareness entirely. This has been measured time and time again by science showing that people actually brace themselves prior to a future noxious stimulus that is not expected but will be foreseen, and then this will trigger an inner recoiling and a kind of steeling oneself to survive the imminent onslaught. So that is the closest parallel with regard to the plant experience in comparison to human threat detection and responses.