Loss of plastid genes in an autotrophic desert plant.

Plant plastid genomes are highly conserved with most flowering plants having the same complement of essential plastid genes. Here, we report the loss of five of the eleven NADH dehydrogenase subunit genes () in the plastid of a desert plant jojoba (). The plastid genome of jojoba was 156,496 bp with one large single copy region (LSC), a very small single copy region (SSC) and two expanded inverted repeats (IRA + IRB). The NADH dehydrogenase (NDH) complex is comprised of several protein subunits, encoded by the genes of the plastome and the nucleus. The genes are critical to the proper functioning of the photosynthetic electron transport chain and protection of plants from oxidative stress. Most plants are known to contain all eleven genes. Plants with missing or defective genes are often heterotrophs either due to their complete or holo- or myco- parasitic nature. Plants with a defective NDH complex, caused by the deletion/pseudogenisation of some or all the genes, survive in milder climates suggesting the likely extinction of plant lineages lacking these genes under harsh climates. Interestingly, some autotrophic plants do exist without gene/s and can cope with high or low light. This implies that these plants are protected from oxidative stress by mechanisms excluding genes. Jojoba has evolved mechanisms to cope with a non-functioning NDH complex and survives in extreme desert conditions with abundant sunlight and limited water.