There is research going on in the industry to make the tire/rubber market more sustainable. Before moving into my answer, I would to like to let you know that this is only one possible method that falls under the category of "naturally derived" and in reality, there is a lot of research being put into the industry to make it more sustainable. The comments on your question also share keystone examples of the same. What I am about to discuss is also not a 100% natural(it is only partly natural).
Isoprene, a crucial precursor for certain synthetic rubbers, is a hydrocarbon typically produced as a by-product during crude oil refining. Using a catalyst, isoprene units are polymerized into long chains to create polyisoprene, which serves as a raw material for manufacturing tires and other products. Traditionally, isoprene is produced as a byproduct of ethylene production from naphtha or gas oil cracking, with yields of only 2–5%. (Source:https://www.ncbi.nlm.nih.gov/books/NBK507534/) The demand for renewable isoprene is driven by its primary use in the production of synthetic rubber for tire manufacturing, with a volume of over 700000 tonnes. (Source: https://www.chemanalyst.com/industry-report/isoprene-rubber-market-762) This conventional method is energy-intensive and involves multiple distillation and extraction steps. Additionally, the shift from naphtha to ethane in steam crackers due to the US shale gas revolution has led to supply shortages and price volatility for isoprene.
Isoprene derived from natural means can be used to make car tires through an innovative hybrid bio/thermochemical process that significantly reduces environmental impact and carbon intensity. This process begins with the efficient fermentation of cellulosic sugars to mevalonolactone (MVL) by genetically engineered Escherichia coli strains. MVL is then converted to isoprene through acid-catalyzed decarboxylation using inexpensive amorphous SiO2/Al2O3 catalysts. This method has been optimized to achieve high isoprene yields, with the highest yield attained over SiO2/Al2O3 containing 90 wt% SiO2 at 250 °C and 1.4 h–1, corresponding to approximately 60% of the theoretical maximum yield. The key to maximizing isoprene formation lies in the Brønsted acidity of the catalyst and operating at mild temperatures (225–250 °C) to prevent secondary oligomerization. (Source: https://pubs.acs.org/doi/10.1021/acscatal.0c01438)
The hybrid bio/thermochemical process offers a more sustainable and stable alternative. Major tire manufacturers, including Goodyear, Bridgestone, and Michelin, have partnered with biotech companies to develop bioisoprene production processes. For instance, Genencor (DuPont) has achieved a fermentation titer of 60 g/L for isoprene with a yield of 0.11 g/g of glucose (Source: https://www.liebertpub.com/doi/10.1089/ind.2010.6.152). However, challenges remain in improving yields and overcoming scale-up issues. Combining biochemical processes with chemocatalytic steps provides a strategic advantage, as demonstrated by the integrated cascade process that efficiently converts cellulosic sugars to isoprene.
By adopting this advanced hybrid process, car tire manufacturers can leverage naturally derived isoprene to produce rubber(this would still be considered to an extent as "synthetic"), contributing to more sustainable and environmentally friendly tire production. This bio-thermochemical process offers a sustainable alternative to traditional isoprene production methods. From an economic standpoint, conventional process also faces supply issues due to the shift from naphtha to ethane in steam crackers, leading to isoprene shortages and price volatility.
But this does not mean that this "green approach" does not have any challenges. Most bio-isoprene production across various cell factories has only produced strains with marginal productivity or either successfully addressed productivity issues but still suffered from low yields. (Source: https://www.sciencedirect.com/science/article/abs/pii/S1096717616300581)
To end it is clear that the industry is still in its infancy. It is important to understand that obtaining a 100% natural rubber ready for commercial use in today's world is very much an ideal situation(as of now). There is more to learn, and one could consider reading about "High performance bio-based elastomers" as well. By developing low roll-resistance green tire elastomers from bio-based chemicals like itaconic acid and conjugated dienes, the industry can significantly reduce fuel consumption, CO2 emissions, and air pollution. Utilizing a molecular structural design with non-petroleum-based silica and tuning the viscoelastic properties of elastomer composites, researchers successfully created green tires that enhance fuel efficiency, reduce dependency on petrochemical resources, and improve performance.(Source: https://pubs.rsc.org/en/content/articlelanding/2016/ta/c6ta05001h) This innovation paves the way for a more sustainable future in the synthetic rubber and automobile industries, which make effective use of natural processes.
