Cassava mosaic disease resistance

 

I was a co-first author on an international collaboration with scientists from NaCRRI in Uganda, UCLA, and ETH Zürich to identify a long-elusive resistance gene to Cassava Mosiac Disease (CMD).

Cassava is a highly heterozygous root crop that feeds nearly a billion people worldwide. Many cassava varieties are severely susceptible to Cassava Mosaic Virus which causes CMD, a viral pandemic devastating cassava yields around the world.

In this research project, recently published in Nature Communications, I led the map-based cloning effort, using GBS and phenotype data from over 3,000 F1 individuals to develop a pipeline to re-map the locus for CMD resistance. I further leveraged my new cassava genome

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Photo: N Taylor

assembly which corrected errors within the locus, to develop a KASP marker based assay and fine map CMD resistance to 190kb. Within the identified region, we found heterozygous non-synonymous mutations in DNA polymerase δ subunit 1 that mediate resistance. Surprisingly, resistance controlled by this locus is lost during tissue culture induced morphogenesis, and it appears to have arisen multiple times as a periclinal chimera in African farmers’ fields.

The manifestation of these resistance alleles as periclinal chimeras may be crucial to the adaption, as it appears that homozygous mutations in this DNA polymerase are lethal. The identification of this gene is an important discovery for millions of subsistence farmers in Africa and around the world. 

Future research is underway to better understand the mechanism with which the resistance alleles of POLD1 mediate virus resistance.