(from @philippbayer)
The classic approach is to use something like BLAST to compare with known sequences, but this has many drawbacks. For starters, in plants the databases lean very heavily towards Arabidopsis thaliana, not more common plants such as maize or wheat.
People do get around this by looking for protein domains (Hidden Markov Models) but that doesn't go very far either, you have to describe domains first, and many are very generic. Can we classify protein/gene sequence using RNN/CNNs? Here's an example where someone tried