Title : Phytochrome a mediated modulation of photosynthesis, development and yield in rice (oryza sativa l.) In fluctuating light environment
Sensory photoreceptors called phytochromes are linked to the photomorphogenesis of plants. A, B, and C are the three phytochromes (phy) found in rice. Rice phytochrome A mutant (phyA) and its wild-type (WT) genotype Akitakomachi were planted in the field to examine the impact of phyA in plant growth, photosynthesis, biomass, and yield under low light (LL) and normal light (NL) situations. Both WT and phyA were shaded by the agro-shade net, which decreased light intensity by around 75%, to induce LL (338 µmole photons m-2 s-1). The experimental control was the NL intensity (1355 µmole photons m-2 s-1). In both NL and LL, the plant height was reduced in phyA mutants by 8% to 10%. In the mutants in NL and to a greater extent in the LL, other developmental metrics such as leaf area index, specific leaf weight, and spikelet fertility decreased. Since phyA's electron transport rate (ETR) was lower, its non-photochemical quenching was higher (NPQ). In LL, phyA considerably outperformed WT in terms of the following metrics: photosynthetic rate, stomatal conductance, transpiration rate, apparent quantum yield, maximal carboxylation efficiency, and mesophyll conductance. Additionally, in phyA under LL, the expression of the rice phytochrome-interacting factor-like protein (OsPIL1) was relatively downregulated. As a result, the amount of total chlorophyll (Chl) and Chl b was decreased, and the ratio of Chl a/b was increased. Additionally, phyA under LL exhibits a substantially lesser upregulation of Fv/Fm and expression of the chlorophyll-a/b-protein isoforms, suggesting a reduced potential for light absorption than WT plants. Grain yield was reduced by 55% more than WT under LL due to a lower total carbon budget in phyA as a result of reduced photosynthesis. Our results showed that phytochrome A played a crucial role in coordinating several shade-acclimation responses to alleviate LL-induced stress and enhance the harvest index in rice.
Keywords: Phytochrome, rice, low light, shade avoidance, grain yield