Transcriptional Comparison of Genes Associated with Photosynthesis, Photorespiration, and Photo-Assimilate Allocation and Metabolic Profiling of Rice Species

The ever-increasing human population alongside environmental deterioration has presented a pressing demand for increased food production per unit area. As a consequence, considerable research effort is currently being expended in assessing approaches to enhance crop yields. One such approach is to harness the allelic variation lost in domestication. This is of particular importance since crop wild relatives often exhibit better tolerance to abiotic stresses. Here, we wanted to address the question as to why wild rice species have decreased grain production despite being characterized by enhanced rates of photosynthesis. In order to do so, we selected ten rice species on the basis of the presence of genome information, life span, the prominence of distribution, and habitat type and evaluated the expression of genes in photosynthesis, photorespiration, sucrose and starch synthesis, sucrose transport, and primary and secondary cell walls. We additionally measured the levels of a range of primary metabolites via gas chromatography–mass spectrometry. The results revealed that the wild rice species exhibited not only higher photosynthesis but also superior CO₂ recovery by photorespiration; showed greater production of photosynthates such as soluble sugars and starch and quick transportation to the sink organs with a possibility of transporting forms such as RFOs, revealing the preferential consumption of soluble sugars to develop both primary and secondary cell walls; and, finally, displayed high glutamine/glutamic acid ratios, indicating that they likely exhibited high N-use efficiency. The findings from the current study thus identify directions for future rice improvement through breeding.