Organelle genome assembly uncovers the dynamic genome reorganization and cytoplasmic male sterility associated genes in tomato

To identify cytoplasmic male sterility(CMS)-associated genes in tomato,we determined the genome sequences of mitochondria and chloroplasts in three CMS tomato lines derived from independent asymmetric cell fusions,their nuclear and cytoplasmic donors,and male fertile weedy cultivated tomato and wild relatives.The structures of the CMS mitochondrial genomes were highly divergent from those of the nuclear and cytoplasmic donors,and genes of the donors were mixed up in these genomes.On the other hand,the structures of CMS chloroplast genomes were moderately conserved across the donors,but CMS chloroplast genes were unexpectedly likely derived from the nuclear donors.Comparative analysis of the structures and contents of organelle genes and transcriptome analysis identified three genes that were uniquely present in the CMS lines,but not in the donor or fertile lines.RNA-sequencing analysis indicated that these three genes transcriptionally expressed in anther,and identified different RNA editing levels in one gene,orf265,that was partially similar to ATP synthase subunit 8,between fertile and sterile lines.The orf265 was a highly potential candidate for CMS-associated gene.This study suggests that organelle reorganization mechanisms after cell fusion events differ between mitochondria and chloroplasts,and provides insight into the development of new F1 hybrid breeding programs employing the CMS system in tomato.

Impacts of Sletr1-1 and Sletr1-2 mutations on the hybrid seed quality of tomatoes

Shelf life is an important breeding trait in tomato, especially for the tomato production in subtropical and tropical regions. Previously we have isolated and characterized ethylene receptor mutants, Sletr1-1 and Sletr1-2 from mutant population based on Micro-Tom cultivar. Sletr1-1 showed insensitivity to ethylene while Sletr1-2 showed reduced sensitivity to ethylene. We also have demonstrated that the traits are useful for extending fruit shelf life of the hybrid tomato cultivars. For commercializing the hybrid cultivars, the seed quality is another important trait. In this study, we evaluated the effects of the Sletr1-1 and Sletr1-2 mutations on the seed quality characteristics of F_1 hybrid lines generated by crossing Sletr1-1 and Sletr1-2 with three commercial tomato cultivars, Intan, Mutiara and Ratna. Sletr1-1 mutation conferred insensitivity to ethylene in the F_1 hybrid seedlings, resulting in negative effects including reduced germination rate, vigor index and emergence speed index. Interestingly Sletr1-2 mutation had almost no effect on the seed quality characteristics of the F_1 hybrid lines, suggesting that Sletr1-2 was suitable for producing high quality of hybrid seeds.

The Cytological Studies on Neglected and Underutilized Cucurbit Species with Special Reference to Chayote,an Under-Exploited Species

Cucurbitaceae family contains important economic and medical crops, they can be divided into two categories according to the worldwide consumption, use, and production. The Cucurbit Popular Crops (CuPoC) are comprised of cucumber, the Cucurbita group (pumpkin and squash), melon and watermelon. On the other hand, Neglected and Underutilized Cucurbit Species (NUCuS) group has been used as food sources, medicinal properties and elements in the elaboration of different types of items. The NUCuS is represented in this review work by bitter gourd, bottle gourd, chayote, ridge gourd, and snake gourd, which are recognized mainly in Asia. The center of origin of the majority of NUCuS was proposed to be in the Old World. In contrast, the origin of chayote or Sechiumedule (Jacq.) Sw. was suggested in the New World, precisely in Mesoamerican region based on linguistic uses and distribution of wild relatives. The environmental factors along with artificial selection, production systems and traditional knowledge have been influenced the evolutionary history of NUCuS, Infraspecific variation of chayote has been reported in Mexico over-described varietal groups. These descriptors were determined based on biochemical and morpho-structural traits;however, cytogenetic analyses are scarce. Specifically, chromosome and nuclear content analyses are important to support botanical groups, analyze artificial selection history, developing breeding and conservation programs. The present review paper discusses agronomic and evolutionary importance based on cytological evidence in NUCuS, mainly in the prominent chayote;with the perspective to prompt breeding, conservation, cytology, structural and functional genomics research for its sustainable utilization.