Recent studies show that overexpression of a short version of the cation exchanger 1 gene (sCAX1) can cause Ca2+ deficiency symptoms in tomato (Solanum lycopersicum L.). However, the Ca2+ deficiency in relation to the overexpression of this gene has not been investigated in potato (Solanum tuberosum L.). The objective of our study was to investigate the production of known Ca2+ deficiency symptoms in potato in relation to the overexpression of sCAX1. Plantlets of S. tuberosum cultivar ‘Atlantic’ overexpressing the sCAX1 gene were produced using Agrobacterium tumefaciens. Transgenic plants grown with normal amounts of Ca2+ under in vitro or greenhouse conditions showed known Ca2+ deficiency symptoms in potato plants such as shoot tips damage and leaf margin necrosis, as well as tuber internal defects (hollow heart). Growing the transgenic plants with higher amounts of Ca2+ in the media or soil nutrient solution mitigated these symptoms. These results support the notion that both shoot tip necrosis and hollow heart are associated with Ca2+ deficiency. There was abundance of calcium oxalate (CaC2O4) crystals present only in the transgenic plants suggesting that these plants sequester Ca2+ in the form of CaC2O4 in the vacuoles of transgenic plants, reducing Ca2+ in the other pools. Since both shoot tip necrosis and hollow heart are known to be associated with poor cell wall health, our results suggest that CAX1 is a regulator of Ca2+ in the cell wall. In support of this concept, we found reduced cell wall biomass in the transgenic plants compared with the wild type.

The Adapting Agriculture to Climate Change Project set out to improve the diversity, quantity, and accessibility of germplasm collections of crop wild relatives (CWR). Between 2013 and 2018, partners in 25 countries, heirs to the globetrotting legacy of Nikolai Vavilov, undertook seed collecting expeditions targeting CWR of 28 crops of global significance for agriculture. Here, we describe the implementation of the 25 national collecting programs and present the key results. A total of 4587 unique seed samples from at least 355 CWR taxa were collected, conserved ex situ, safety duplicated in national and international genebanks, and made available through the Multilateral System (MLS) of the International Treaty on Plant Genetic Resources for Food and Agriculture (Plant Treaty). Collections of CWR were made for all 28 targeted crops. Potato and eggplant were the most collected genepools, although the greatest number of primary genepool collections were made for rice. Overall, alfalfa, Bambara groundnut, grass pea and wheat were the genepools for which targets were best achieved. Several of the newly collected samples have already been used in pre-breeding programs to adapt crops to future challenges.

Consistent with reports on other plants we recently reported that a potato transgenic line (AT010901) overexpressing sCAX1 show classic symptoms of calcium deficiency shoot tip injury, leaf curling, leaf margin necrosis and tuber internal defects such as hollow heart and brown spots. The present study was undertaken to quantify calcium in various fraction of leaf and tuber tissues of this transgenic and wild type potato clones to understand the development of these deficiency symptoms at normal calcium nutrition (1mM) and its mitigation at higher calcium nutrition (10mM). Plants were grown in controlled environment growth chamber and watered with balanced nutrient solution containing either 1 or 10 mM calcium. The plants overexpressing sCAX1 showed calcium deficiency symptoms while sequestering calcium in the vacuole as calcium oxalate crystals. Various fractions of calcium were qualified in the young and mature leaves as well as tuber tissue. A reduced concentration of water soluble fraction of calcium was most important factor related to the development of calcium deficiency symptoms in the line overexpressing sCAX1. Furthermore, an increase in this fraction appear to explain the alleviation of the deficiency symptoms in these transgenic plants.Ours is the first study to document the significance of water-soluble calcium in the development of calciumdeficiency symptoms in the potato transgenic lines overexpressing sCAX1. Furthermore, our result demonstrates that an increase in this fraction plays a significant role in the alleviation of calcium deficiency symptoms when calcium concentration in the nutrient media is increased. These results provide important insight on the role of sCAX1 in the calcium homeostasis.

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Tomato (Solanum lycopersicum) is a crop of global importance that has center of origin in Peru, with 11 species of wild relatives (CWR) occurring in the country. These CWR contain genetic material that could be used to improve currently cultivated species, and that is usually stored ex situ in germplasm banks. Hence, assessing the representativeness of germplasm banks is important to strengthen genetic improvement of tomatoes as well as their resilience to globally changing conditions. Here, we used gap analysis methodology on the 11 species of tomato CWR occurring in Peru. This methodology consists in seven steps that consider representativeness in terms of herbaria/germplasm banks, geography and environments within the country, in order to establish conservation priorities. We also assessed conservation priorities for the Instituto Nacional de Innovación Agraria (INIA), which is the main ex situ conservation Institution in Peru. Nationally, we found one species with high priority for conservation: Solanum huaylasense, and for INIA we found six species with high conservation priority: S. huaylasense, S. neorickii, S. chmielewskii, S. corneliomulleri, S. arcanum and S. chilense. We also found that the gap analysis methodology allowed for a proper prioritization of species and be readily applied to other species. We conclude by recommending strategies to improve the genetic coverage of the tomato germplasm held at INIA, as well as by discussing priorities for in situ conservation of tomato CWRs.