Role of Na+ transporters HKT1;1 and HKT1;2 in tomato salt tolerance. I. Function loss of cheesmaniae alleles in roots and aerial parts

We wish to thank Elena Sanchez Romero (EEZ-CSIC) for her technical assistance, the Scientific Instrumentation Service at EEZ-CSIC, Granada, for their ICP-OES mineral analysis and Michael O'Shea for proofreading the manuscript. The study was funded by grant AGL201782452-C2-1R (A.B.) and grant AGL2017-82452-C2-2R (M.J.A.), both from the Spanish Ministerio de Ciencia e Innovacion/Agencia Estatal de Investigacion, MCIN/AEI/10.13039/501100011033, and FEDER "Una manera de hacer Europa", as well as grant ACCESP2018 (J.A.T.) from the University of Granada. J.E. was supported by a JAE Intro-CSIC grant, JAEINT_19_00566.We analyzed the physiological impact of function loss on cheesmaniae alleles at the HKT1;1 and HKT1;2 loci in the roots and aerial parts of tomato plants in order to determine the relative contributions of each locus in the different tissues to plant Na+/K+ homeostasis and subsequently to tomato salt tolerance. We generated different reciprocal rootstock/scion combinations with non-silenced, single RNAi-silenced lines for ScHKT1;1 and ScHKT1;2, as well as a silenced line at both loci from a near isogenic line (NIL14), homozygous for the Solanum cheesmaniae haplotype containing both HKT1 loci and subjected to salinity under natural greenhouse conditions. Our results show that salt treatment reduced vegetative growth and altered the Na+/K+ ratio in leaves and flowers; negatively affecting fruit production, particularly in graft combinations containing single silenced ScHKT1;2- and double silenced ScHKT1;1/ScHKT1;2 lines when used as scion. We concluded that the removal of Na+ from the xylem by ScHKT1;2 in the aerial part of the plant can have an even greater impact than that on Na+ homeostasis at the root level under saline conditions. Also, ScHKT1;1 function loss in rootstock greatly reduced the Na+/K+ ratio in leaf and flower tissues, minimized yield loss under salinity. Our results suggest that, in addition to xylem Na+ unloading, ScHKT1;2 could also be involved in Na+ uploading into the phloem, thus promoting Na+ recirculation from aerial parts to the roots. This recirculation of Na+ to the roots through the phloem could be further favoured by ScHKT1;1 silencing at these roots.Spanish Ministerio de Ciencia e Innovacion/Agencia Estatal de Investigacion AGL2017-82452-C2-1R AGL2017-82452-C2-2RFEDER "Una manera de hacer Europa" MCIN/AEI/10.13039/501100011033University of Granada ACCESP2018JAE Intro-CSIC grant JAEINT_19_0056

Inheritance of Rootstock Effects and Their Association with Salt Tolerance Candidate Genes in a Progeny Derived from 'Volkamer' Lemon

A seedling population from hybrids between ‘Volkamer’ lemon (Citrus volkameriana) and ‘Rubidoux’ trifoliate orange (Poncirus trifoliata) was grafted with ‘Hashimoto’ Satsuma mandarin (Citrus unshiu) to study the inheritance of rootstock effects on salt tolerance in terms of fruit yield. Trees were maintained in a screenhouse, and a salt treatment (25 mm NaCl) was applied to 32 genotypes from June to September every year for 5 years. Rootstocks were genotyped for five salt tolerance candidate genes. Significant effects of rootstock genotype (G) and treatment (E) were found for most traits. Salinity decreased yield and juice volume but improved soluble solids concentration (TSS) and rind thickness. Year effects were highly significant in most cases. G × E interactions were found for fruit weight, total fruit weight, juice volume (JV), leaf water content (LWC), and leaf [Na+]. Therefore, rootstocks that induce early fruit maturation under salinity (by increasing TSS and maintaining JV) can be selected to expand the harvesting calendar of mandarin cultivars. Salt tolerance candidate genes SOS1 and NHX1 were associated with fruit yield traits under normal conditions (1.4 dS·m−1), and SOS1 and CCC were associated with LWC under salinity conditions (4 dS·m−1). Only 5% progeny induced higher accumulated yield than ‘Volkamer’ lemon under salinity. Given the low heritability of rootstock effects on fruit yield under salinity conditions (0.18 at most), marker-assisted selection might be useful

HKT1;1 and HKT1;2 Na+ Transporters from Solanum galapagense Play Different Roles in the Plant Na+ Distribution under Salinity

Salt tolerance is a target trait in plant science and tomato breeding programs. Wild tomato accessions have been often explored for this purpose. Since shoot Na+/K+ is a key component of salt tolerance, RNAi-mediated knockdown isogenic lines obtained for Solanum galapagense alleles encoding both class I Na+ transporters HKT1;1 and HKT1;2 were used to investigate the silencing effects on the Na and K contents of the xylem sap, and source and sink organs of the scion, and their contribution to salt tolerance in all 16 rootstock/scion combinations of non-silenced and silenced lines, under two salinity treatments. The results show that SgHKT1;1 is operating differently from SgHKT1;2 regarding Na circulation in the tomato vascular system under salinity. A model was built to show that using silenced SgHKT1;1 line as rootstock would improve salt tolerance and fruit quality of varieties carrying the wild type SgHKT1;2 allele. Moreover, this increasing effect on both yield and fruit soluble solids content of silencing SgHKT1;1 could explain that a low expressing HKT1;1 variant was fixed in S. lycopersicum during domestication, and the paradox of increasing agronomic salt tolerance through silencing the HKT1;1 allele from S. galapagense, a salt adapted species

Control genético de caracteres reproductivos bajo diferentes regímenes de temperatura en poblaciones segregantes de tomate

El aumento de temperatura producido por el calentamiento global del planeta tiene a la agricultura entre los principales sectores afectados, provocando una disminución en la producción de la mayoría de los cultivos de regiones templadas y tropicales. En el caso del tomate, ampliamente cultivado en esas áreas geográficas, las altas temperaturas producen daños tanto a nivel fisiológico como morfológico afectando a los órganos reproductivos. Por ello, en este trabajo, se ha estudiado el control genético de caracteres reproductivos en varias poblaciones de líneas consanguíneas derivadas de los cruces entre entradas de S. pimpinelifolium y cultivares de tomate (MoneyMaker x TO-937, E9xL5 and E6203xLA1589) y entre cultivares tolerantes y sensibles a altas temperaturas cultivadas en diferentes condiciones de estrés térmico

Combining Genetic and Transcriptomic Approaches to Identify Transporter-Coding Genes as Likely Responsible for a Repeatable Salt Tolerance QTL in Citrus

The excessive accumulation of chloride (Cl−) in leaves due to salinity is frequently related to decreased yield in citrus. Two salt tolerance experiments to detect quantitative trait loci (QTLs) for leaf concentrations of Cl−, Na+, and other traits using the same reference progeny derived from the salt-tolerant Cleopatra mandarin (Citrus reshni) and the disease-resistant donor Poncirus trifoliata were performed with the aim to identify repeatable QTLs that regulate leaf Cl− (and/or Na+) exclusion across independent experiments in citrus, as well as potential candidate genes involved. A repeatable QTL controlling leaf Cl− was detected in chromosome 6 (LCl-6), where 23 potential candidate genes coding for transporters were identified using the C. clementina genome as reference. Transcriptomic analysis revealed two important candidate genes coding for a member of the nitrate transporter 1/peptide transporter family (NPF5.9) and a major facilitator superfamily (MFS) protein. Cell wall biosynthesis- and secondary metabolism-related processes appeared to play a significant role in differential gene expression in LCl-6. Six likely gene candidates were mapped in LCl-6, showing conserved synteny in C. reshni. In conclusion, markers to select beneficial Cleopatra mandarin alleles of likely candidate genes in LCl-6 to improve salt tolerance in citrus rootstock breeding programs are provided

Contribución de la raíz a la sostenibilidad y resiliencia de los cultivos de tomate y cítricos

El sistema agrario está basado en un conjunto de variedades generalmente seleccionadas bajo condiciones óptimas de cultivo por lo que su acervo genético representa una muestra muy reducida de los genes existentes en los recursos fitogenéticos de las especies cultivadas. La raíz tiene un papel fundamental en la adquisición de agua y nutrientes y en la interacción de la planta con los microorganismos del suelo por lo que el uso de patrones puede ser una buena estrategia para aumentar la sostenibilidad y resiliencia de los cultivos de cítricos y tomate utilizando nuevo germoplasma. A pesar de que el uso del injerto está muy extendido desde hace mucho tiempo, se desconoce el porqué de la mayoría de sus acciones beneficiosas. En el seminario se expondrán los sistemas biológicos y herramientas (análisis de QTL) que utilizamos para explorar los recursos fitogenéticos y descubrir que pueden ser beneficiosos en la mejora de patrones de estas especie