YSL3-mediated copper distribution is required for fertility, grain yield, and size in Brachypodium

Abstract

35Addressing the looming global food security crisis requires the development of high yielding 36 crops. In this regard, the deficiency for the micronutrient copper in agricultural soils 37 decreases grain yield and significantly impacts a globally important crop, wheat. In cereals, 38 grain yield is determined by inflorescence architecture, flower fertility, grain size and weight. 39 Whether copper is involved in these processes and how it is delivered to the reproductive 40 organs is not well understood. We show that copper deficiency alters not only the grain set 41 but also flower development in both wheat and it's recognized model, Brachypodium 42 distachyon, We then show that a brachypodium yellow-stripe-like 3 (YSL3) transporter 43 localizes to the phloem and mediates copper delivery to flag leaves, anthers and pistils. 44 Failure to deliver copper to these structures in the ysl3 CRISPR/Cas9 mutant results in 45 delayed flowering, altered inflorescence architecture, reduced floret fertility, grain number, 46 size, and weight. These defects are rescued by copper supplementation and are complemented 47 by the YSL3 cDNA. This new knowledge will help to devise sustainable approaches for 48 improving grain yield in regions where soil quality is a major obstacle for crop production. 49 50Global food security and the demand for high-yielding grain crops are among the most urgent 51 drivers of modern plant sciences due to the current trend of population growth, extreme 52 weather conditions and decreasing arable land resources [1]. The grain yield is directly linked 53 to the crop and soil fertility. In this regard, it has been known for decades that the deficiency 54 for the micronutrient copper in alkaline, coarse-textured or organic soils that occupy more 55 than 30% of the world arable land, compromises crop fertility, reduces grain/seed yield and in 56 acute cases results in crop failure [2][3][4][5]. In accord with the essential role of copper in 57 reproduction, recent studies using synchrotron x-ray fluorescent (SXRF) microscopy 58 established that copper localizes to anthers and pistils of flowers in a model dicotyledonous 59 species, Arabidopsis thaliana, and failure to deliver copper to these reproductive organs 60 severely compromises fertility and seed set [6]. Although copper deficiency can be remedied 61 by the application of copper-based fertilizers, this approach is not environmentally friendly 62 and can lead to the build-up of toxic copper levels in soils [2,5,7]. Mineral nutrient 63 transporters have been recognized as key targets for improving the mineral use efficiency in 64 sustainable crop production [8]. Wheat is the world's third important staple crop after maize 65 (Zea mays) and rice (Oryza sativa); however, wheat grain yield remained relatively low under 66 marginal growing environments despite significant breeding efforts [9]. Wheat is also 67 regarded as the most sensitive to copper deficiency [2, 3,5]. How copper uptake and internal 68 transport is achieved in wheat and how it af...

Copper deficiency alters shoot architecture and reduces fertility of both gynoecium and androecium inArabidopsis thaliana

“…The defect in pollen fertility was also observed in A. thaliana, B. distachyon, and Oryza sativa mutants lacking transporters that mediate copper delivery to reproductive organs (Chu et al, 2010;Sheng et al, 2019;Zhang et al, 2018a). We show that adding copper directly to the pollen germination medium rescued pollen germination defect of copper-deficient A. thaliana (Fig.…”

“…By contrast, phosphorus deficiency delays flowering (Kant et al, 2011). Our observations presented here and in Sheng et al, 2019 show that copper deficiency delays flowering in A. thaliana and B. distachyon. It is unclear, however, whether delayed flowering under copper deficiency is a result of slower growth rates due to reduced photosynthesis and respiration and/or a delayed developmental transition from the vegetative-to-reproductive stage.…”

“…It has been known for decades that deficiency in the micronutrient copper in alkaline soils compromises plant fertility with the most negative impact on wheat grain production (Broadley et al, 2012;Graham, 1978;Graves and Sutcliffe, 1974;Shorrocks and Alloway, 1988;Solberg et al, 1999). In-line with the essential role of copper in plant reproduction, recent studies using synchrotron x-ray fluorescence microscopy have shown that the bulk of copper is associated with anthers and pistils in Arabidopsis thaliana and Brachypodium distachyon and failure to transport copper to reproductive structures in these species and Oryza sativa significantly reduces fertility (Sheng et al, 2019;Yan et al, 2017;Zhang et al, 2018a).…”

“…Because metabolically active papillar cells are required for successful pollen tube growth (Kandasamy et al, 1993), the infertility of gynoecium of copper-deficient plants might be, in part, caused by a defect in papillae formation. It is noteworthy that the defect in copper delivery to reproductive organs in the mutant lacking copper transporter YSL3 also leads to aberrant stigma formation in B. distachyon (Sheng et al, 2019). Why copper deficiency causes defects in stigma morphology is unclear.…”

Copper deficiency alters shoot architecture and reduces fertility of both gynoecium and androecium in Arabidopsis thaliana

“…distachyon and failure to transport copper to reproductive structures in these species and Oryza sativa significantly reduces fertility (Sheng et al, 2019;Yan et al, 2017;Zhang, Lu, et al, 2018).…”