Abstract
A fundamental factor to improve crop productivity involves the optimization of reduced carbon translocation from source to sink tissues. Here, we present data consistent with the positive effect that the expression of the Arabidopsis thaliana H+-PPase (AVP1) has on reduced carbon partitioning and yield increases in wheat. Immunohistochemical localization of H+-PPases (TaVP) in spring wheat Bobwhite L. revealed the presence of this conserved enzyme in wheat vasculature and sink tissues. Of note, immunogold imaging showed a plasma membrane localization of TaVP in sieve element- companion cell complexes of Bobwhite source leaves. These data together with the distribution patterns of a fluorescent tracer and [U14C]-sucrose are consistent with an apoplasmic phloem-loading model in wheat. Interestingly, 14C-labeling experiments provided evidence for enhanced carbon partitioning between shoots and roots, and between flag leaves and milk stage kernels in AVP1 expressing Bobwhite lines. In keeping, there is a significant yield improvement triggered by the expression of AVP1 in these lines. Green house and field grown transgenic wheat expressing AVP1 also produced higher grain yield and number of seeds per plant, and exhibited an increase in root biomass when compared to null segregants. Another agriculturally desirable phenotype showed by AVP1 Bobwhite plants is a robust establishment of seedlings.
Highlights
According to the Food and Agriculture Organization of the United Nations, wheat (Triticum aestivum L.) is the largest primary commodity in the world, cultivated on more land area than any other commercial crop (∼220 Mha) with global production of over 700 million tons, a total global annual export value of close to US$50 billion, and accounts for a fifth of our total available dietary calories1
We show evidence consistent with the expression of AVP1 augmenting carbon partitioning from source to sinks in wheat plants by either empowering the flux of carbon via phloem loading and transport, or by strengthening the sinks, which translates into improved yield
Characterized antiserum (Li et al, 2005; Park et al, 2005) generated against the highly conserved CTKAADVGADLVGKIE motif (Rea et al, 1992) in H+-PPases was used in this experiment, that showed a distinct band at the expected size (∼80 kDa) when immunoblotted against the total protein extracted from wheat seedlings (Figure 1A)
Summary
According to the Food and Agriculture Organization of the United Nations, wheat (Triticum aestivum L.) is the largest primary commodity in the world, cultivated on more land area than any other commercial crop (∼220 Mha) with global production of over 700 million tons, a total global annual export value of close to US$50 billion, and accounts for a fifth of our total available dietary calories. The synthesis of primary photosynthate, sucrose (Suc), in wheat starts with carbon fixation into triose phosphates in the photoautotrophic mesophyll cells in source leaves. It is either transiently stored in chloroplasts and vacuoles, or is transported via the phloem to heterotrophic sink tissues and/or used as the substrate for starch reserves in the grain endosperm (Trethewey and Smith, 2000; Bahaji et al, 2014; Griffiths et al, 2016; Kumar et al, 2018). Anatomical (Kuo et al, 1974) and micro-autoradiography studies (Altus and Canny, 1982, 1985) suggested a passive symplasmic path for sucrose loading in wheat source leaves
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