Phytochrome A mediated modulation of photosynthesis, development and yield in rice (Oryza sativa L.) in fluctuating light environment

Abstract

Phytochromes are sensory photoreceptors associated with the photomorphogenesis of plants. Rice has 3 phytochromes (phy); phyA, phyB and phyC. To understand the role of phyA under low light (LL) and normal light (NL) environments in plant growth, photosynthesis, biomass and yield, rice phytochrome A mutant (phyA) along with its wild-type (WT) genotype Akitakomachi were grown in field conditions. To induce LL (∼338 μmole photons m−2 s−1) both WT and phyA were shaded by the agro-shade net that reduced light intensity by ∼75%. The NL intensity (∼1355 μmole photons m−2 s−1) served as the experimental control. The plant height decreased by 8%−10% in phyA mutants both in NL and LL. Other developmental parameters, leaf area index, specific leaf weight, and spikelet fertility declined in the mutants in NL and to a larger extent in the LL. phyA had a lower electron transport rate (ETR), which increased its non-photochemical quenching (NPQ). The photosynthetic rate (PN), stomatal conductance(gs), transpiration rate (E), apparent quantum yield (AQE), maximum carboxylation efficiency (Vcmax) and mesophyll conductance (gm) significantly decreased in phyA than WT in LL. Furthermore, the expression of rice phytochrome-interacting factor-like protein (OsPIL1) was relatively downregulated in phyA under LL, resulting in a reduced total chlorophyll (Chl) and Chl b content and an increased Chl a/b ratio. Additionally, a relatively lower upregulation of Fv/Fm and expression of the isoforms of chlorophyll-a/b-proteins in phyA under LL suggests its inferior light-harvesting capacity compared to WT plants. Reduced PN resulted in a lowered overall carbon budget in phyA that hampered grain yield by 55% more than WT under LL. Our findings demonstrated the critical role of phytochrome A in orchestrating a series of shade-acclimation responses to salvage LL-induced stress and optimize the harvest index in rice.