The question about the relationship between buddha-nature and the aggregates occurred to me when I was reading Ringu Tulku's commentary to one of Gampopa's works. So, let's see first a Mahamudra work on the topic."The aggregates, the elements and the sense factors of beings have all from the beginning the true nature of awakened male and female buddhas and deities. As it is taught in all sutras and tantras, they are themselves buddha mind.
If, on the contrary, you assume that there is another superior buddha mind to be attained outside of your mind and believe that it is impossible that the extremely pure buddha mind exists within the mind stream of impure beings, that this is nothing but glossing things over and misinterpreting the vajra words of the secret mantra, you have distorted the meaning of the abiding nature and this is improper."
(Wangchug Dorje: Ocean of True Meaning, p 209-210, tr. Henrik Havlat)
Next, here is a Yogacara interpretation (note that there can be other Yogacara views, also note that what is discussed in the following passage from Xuanzang is not identical to the doctrine of "universal buddha-gotra" since there are several gotras):"The 'meritorious qualities' (gunas) and the bodies and lands of the Tathagatas are comprised in the Skandhas, Ayatanas, and Dhatus, as it is fitting that they should be so comprised; but the Skandhas, etc., may be pure (anasrava) or impure (sasrava). ... It is certain that the qualities, bodies, etc., of the Buddha are comprised in the Dhatus. - Why? Because, according to the texts, all Samskrtas (conditioned dharmas) are comprised in the five Skandhas, all dharmas are comprised in the eighteen Dhatus and the twelve Ayatanas ; there is no nineteenth Dhatu (Vimalakirti). ... Let us therefore conclude that the eighteen Dhatus are found in the body of the Buddha but are absolutely pure (anasrava)."
(Ch'eng Wei-Shih Lun, p 787-789, tr. Wei Tat)
The Tiantai understanding of buddha-nature is also interesting, as it is used to cover the entire path as shown in this essay: T'ien-t'ai Chih-i's Concept of Threefold Buddha Nature - A Synergy of Reality, Wisdom, and Practice
. It is useful to have a deeper appreciation of Dogen's presentation of the subject in his writing on buddha-nature (Bussho PDF
). He writes (with reference to a passage in the Platform Sutra where Huineng explains buddha-nature as impermanent to a monk asking about the Nirvana Sutra),"Therefore, that the grasses, trees, thickets and groves are impermanent is the buddha nature; that humans and things, body and mind are impermanent — this is because they are the buddha nature. That the lands, mountains, and rivers are impermanent — this is the buddha nature. Annuttara-samyak-saṃbodhi, because it is the buddha nature, is impermanent; the great parinirvāṇa, because it is impermanent, is the buddha nature. All those with the small views of the two vehicles and the tripiṭaka master teachers of the sūtras and treatises should be “alarmed, dubious, and frightened” at these words of the Sixth Ancestor. If they are alarmed and dubious, they are grouped with Māra and the aliens."
Also (with reference to a Zen story where Nagarjuna manifested the buddha-nature by appearing as full moon),"Though the buddha nature has a “spacious clarity” that takes a “shape like” “the full moon,” it is not the case that it lines up with the “round moon form,” let alone that its “explanation” is “sound or sight,” or its “body manifesting” is form and mind, or the aggregates, fields, and elements. Even if we say it completely resembles the aggregates, fields, and elements, it is “showing by which”; it is “the body of the buddhas.” ... The buddha body is the body manifesting, has a buddha nature that is the body manifesting. Even the measure of a buddha or the measure of an ancestor that speaks of and understands it as the four major elements and five aggregates is the hurried act of the body manifesting. Since we have called them “the body of the buddhas,” the aggregates, fields, and elements are like this."