Physiological and transcriptomic analyses of a yellow-green mutant with high photosynthetic efficiency in wheat (Triticum aestivum L.)

Abstract

Optimizing the antenna size by reducing the chlorophyll (Chl) content is an effective strategy to improve solar energy conversion efficiencies in dense crop monocultures. To elucidate the physiological and molecular mechanisms that regulate Chl biosynthesis and understand the effects of lower Chl content on the photosynthetic process, a light-intensity-dependent yellow-green wheat mutant (Jimai5265yg) was characterized to determine its morphological, histological, physiological, and transcriptional differences with wild type. In addition to lower Chl content with a higher Chl a/b ratio, Jimai5265yg has spherical chloroplasts with few plastoglobule. It is counterintuitive that the photochemical quantum yield of both photosystem I and photosystem II and the following CO assimilation rate significantly increased, but the value of nonphotochemical quenching decreased, indicating a reduction of the photoprotective capacity of this yellow-green mutant. Analysis of intermediate pools and the expression of genes in the Chl synthesis pathway indicated that Mg-protoporphyrin IX (Mg-Proto IX) synthesis was partially blocked due to the imbalanced expression of Mg-chelatase subunits. Interestingly, the expression of photosynthesis-associated nuclear genes (PhANGs) was upregulated, resembling gun mutants which have defects in the Mg-Proto IX-mediated plastid-to-nucleus signaling pathway. A genetic analysis indicated that the yellow-green phenotype was controlled by two nuclear recessive genes located on chromosomes 4AL and 4BL. Jimai5265yg is a novel chlorina mutant which could be used for understanding photosynthesis improvement mechanisms.

The anatomical, physiological, and molecular analysis of a chlorophyll-deficient mutant in tree peony (Paeonia suffruticosa)

“…Then, there could be no doubt that the higher contents of Chl a in yl1 mutant could increase photosynthetic capacity more effectively than in the wild type. In addition, the chloroplast were located deep in the leaves of yl1 mutant with less Chl, which could theoretically obtain more penetration light, and an increased Ci value could provide a higher CO2 supply (Wang et al 2018). Therefore, in the presence of a high proportion of Chl a, the photosynthetic capacity of the yl1 mutant would be improved.…”

“…Chlorophylls (Chl) play a key role in the absorption, transfer, and conversion of light energy in photosynthetic organisms (Wang et al 2018). Chl biosynthesis involves a series of enzymatic steps from glutamyl-tRNA to Chl b (Nagata et al 2005, Wu et al 2007.…”

“…Chl is synthesized in the grana of thylakoids, which assembles with Chl-binding proteins, and is inserted into thylakoid membranes of chloroplasts. The synthesis of Chl and plastid development is interdependent and inseparable (Yang et al 2012, Wang et al 2018. There are about 3,000 proteins in the chloroplast (Timmis et al 2004, Reumann et al 2005; these proteins play important roles in the transition from proplastids to mature chloroplasts, and some of them are involved in the synthesis and regulation of photosynthetic system, etc.…”

“…Leaf color mutant is a valuable material in scientific research; it has been applied widely in chloroplast development research (Li et al 2014, Zhang et al 2017, Chl biosynthesis pathway (Yang et al 2012, photosynthetic regulation , Yang et al 2018, genetic breeding of higher plants, and other fields. Leaf color mutants have been identified in various plants, and most of them have been characterized in woody and cereal crops including tea , rice , Zhao et al 2014, Wang et al 2015, wheat (Wang et al 2018), etc. So far, a lot of work has been done on the mechanism of leaf color variation.…”

“…Due to the partial block in the step of Mg-protoporphyrin IX synthesis, the yellow-green mutant Jimai5265yg in wheat had spherical chloroplasts with few plastoglobuli, lower Chl content with a higher Chl a/b ratio (Wang et al 2018).…”