Characterization of a Chickpea Mutant Resistant to Phelipanche aegyptiaca Pers. and Orobanche crenata Forsk.

Chickpea (Cicer arietinum L.) is a major pulse crop in Israel grown on about 3000 ha spread, from the Upper Galilee in the north to the North-Negev desert in the south. In the last few years, there has been a gradual increase in broomrape infestation in chickpea fields in all regions of Israel. Resistant chickpea cultivars would be simple and effective solution to control broomrape. Thus, to develop resistant cultivars we screened an ethyl methanesulfonate (EMS) mutant population of F01 variety (Kabuli type) for broomrape resistance. One of the mutant lines (CCD7M14) was found to be highly resistant to both Phelipanche aegyptiaca and Orobanche crenata. The resistance mechanism is based on the inability of the mutant to produce strigolactones (SLs)-stimulants of broomrape seed germination. LC/MS/MS analysis revealed the SLs orobanchol, orobanchyl acetate, and didehydroorobanchol in root exudates of the wild type, but no SLs could be detected in the root exudates of CCD7M14. Sequence analyses revealed a point mutation (G-to-A transition at nucleotide position 210) in the Carotenoid Cleavage Dioxygenase 7 (CCD7) gene that is responsible for the production of key enzymes in the biosynthesis of SLs. This nonsense mutation resulted in a CCD7 stop codon at position 70 of the protein. The influences of the CCD7M14 mutation on chickpea phenotype and chlorophyll, carotenoid, and anthocyanin content were characterized.

Novel Mutation in the Acetohydroxyacid Synthase (AHAS), Gene Confers Imidazolinone Resistance in Chickpea Cicer arietinum L. Plants.

Chickpea (Cicer arietinum L.) is an important crop in crop-rotation management in Israel. Imidazolinone herbicides have a wide spectrum of weed control, but chickpea plants are sensitive to acetohydroxyacid synthase (AHAS; also known as acetolactate synthase [ALS]) inhibitors. Using the chemical mutagen ethyl methanesulfonate (EMS), we developed a chickpea line (M2033) that is resistant to imidazolinone herbicides. A point mutation was detected in one of the two genes encoding the AHAS catalytic subunit of M2033. The transition of threonine to isoleucine at position 192 (203 according to Arabidopsis) conferred resistance of M2033 to imidazolinones, but not to other groups of AHAS inhibitors. The role of this substitution in the resistance of line M2033 was proven by genetic transformation of tobacco plants. This resistance showed a single-gene semidominant inheritance pattern. Conclusion: A novel mutation, T192I (T203I according to Arabidopsis), providing resistance to IMI herbicides but not to other groups of AHAS inhibitors, is described in the AHAS1 protein of EMS-mutagenized chickpea line M2033.

CaGLK2 regulates natural variation of chlorophyll content and fruit color in pepper fruit.

KEY MESSAGE: We provide multiple evidences that CaGLK2 underlies a quantitative trait locus controlling natural variation in chlorophyll content and immature fruit color of pepper via modulating chloroplast compartment size. Pepper fruit quality is attributed to a variety of traits, affecting visual appearance, flavor, chemical composition and nutritional value. Among the quality traits, fruit color is of primary importance because the pigments that confer color are associated with nutrition, health and flavor. Although gene models have been proposed for qualitative aspects of fruit color, large natural variation in quantitative pigment content and fruit color exists in pepper. However, its genetic basis is largely unknown which hampers its utilization for plant improvement. We studied the role of GLK2, a GOLDEN2-like transcription factor that regulates chloroplast development in controlling natural variation for chlorophyll content and immature fruit color of pepper. The role of GLK2 in regulating fruit development has been studied previously in tomato using ectopic expression and the uniform ripening mutant analyses. However, pepper provides a unique opportunity to further study the function of this gene because of the wide natural variation of fruit colors in this species. Segregation, sequencing and expression analyses indicated that pepper GLK2 (CaGLK2) corresponds to the recently reported pc10 QTL that controls chloroplast development and chlorophyll content in pepper. CaGLK2 exerts its effect on chloroplast compartment size predominantly during immature fruit development. We show that the genetic background, sequence variation and expression pattern confer a complex and multi-level regulation of CaGLK2 and fruit color in Capsicum. The positive effect on fruit quality predominantly at the green stage conferred by CaGLK2 can be utilized to breed green pepper varieties with improved nutritional values and taste.