Identifying leaf anatomy and metabolic regulators that underpin C ₄ photosynthesis in Alloteropsis semialata

C ₄ photosynthesis is a complex trait requiring multiple developmental and metabolic alterations. Despite this complexity, it has independently evolved over 60 times. However, our understanding of the transition to C ₄ is complicated by the fact that variation in photosynthetic type is usually segregated between species.

Here, we perform a genome wide association study (GWAS) using the grass Alloteropsis semialata , the only known species to have C ₃ , intermediate, and C ₄ accessions. We aimed to identify genomic regions associated with the strength of the C ₄ cycle (measured using δ ¹³ C), and the development of C ₄ leaf anatomy.

Genomic regions correlated with δ ¹³ C include regulators of C ₄ decarboxylation enzymes ( RIPK ), non-photochemical quenching ( SOQ1 ), and the development of Kranz anatomy ( SCARECROW-LIKE ). Regions associated with the development of C ₄ leaf anatomy in the intermediate accessions contain additional leaf anatomy regulators, including those responsible for vein patterning ( GSL8 ) and meristem determinacy ( GRF1 ).

The detection of highly correlated genomic regions with a modest sample size indicates that the emergence of C ₄ photosynthesis in A. semialata required a few loci of large effect. The candidate genes could prove to be relevant for engineering C ₄ leaf anatomy in C ₃ species.