Screening of Mutants Related to the C4 Photosynthetic Kranz Structure in Foxtail Millet

Abstract

C4 plants exhibit significantly higher photosynthetic, water and nutrient use efficiency compared with C3 plants. Kranz anatomy is associated with many C4 plants in which bundle sheath cells surround the veins and are themselves surrounded by mesophyll cells. This specialized Kranz anatomy is elucidated as an important contributor to C4 photosynthetic activities in C4 plant. Characterizing the molecular basis of Kranz structure formation has become a key objective for studies of C4 photosynthesis. However, severe mutants that specifically disrupt Kranz anatomy have not been identified. In this study, we detected 549 stable ethyl methane sulfonate-induced foxtail millet (cultivar Yugu1) mutants related to leaf development and photosynthesis among 2,709 mutants screened (M3/M4 generation). The identified mutants included 52 that had abnormal leaf veins (with abnormal starch accumulation based on iodine staining). Each of the 52 mutants was characterized through an analysis of leaf morphology, and through microscopic observations of leaf tissue sections embedded in resin and paraffin. In total, 14 mutants were identified with abnormal Kranz structures exemplified by small bundle sheath cell size. Additional phenotypes of the mutants included poorly differentiated mesophyll and bundle sheath cells, increased vein density and the absence of chloroplasts in the bundle sheath cells. Kranz structure mutations were accompanied by varying leaf thickness, implying these mutations induced complex effects. We identified mutations related to Kranz structure development in this trial, which may be useful for the mapping and cloning of genes responsible for mediating Kranz structure development.

Photosynthesis in a Changing Global Climate: Scaling Up and Scaling Down in Crops

“…2002; Luo et al, 2018;Döring et al, 2019). Knowledge obtained from mutant screenings can reveal new chloroplast functions, including those necessary for high photosynthetic performance, and accelerate the molecular characterization required for deciphering the genetic basis of plant photosynthesis for future improvements.…”

“…The functional dissection of photosynthesis can be undertaken also by forward genetic screens. Strategies, identification, insights and mutant effects have been reviewed previously ( Somerville, 1986 ; Parinov and Sundaresan, 2000 ; Page and Grossniklaus, 2002 ; Luo et al, 2018 ; Döring et al, 2019 ). Knowledge obtained from mutant screenings can reveal new chloroplast functions, including those necessary for high photosynthetic performance, and accelerate the molecular characterization required for deciphering the genetic basis of plant photosynthesis for future improvements.…”

“…However, when starting any experiment, a set of standard A-Ci curves should be performed to test that the method is working for each species and/or environmental condition. Therefore, this RACiR methodology only appears to be worth the effort when analyzing hundreds of samples at the same environmental condition as is often the case for GWAS and/or QTL experiments ( Dhanapal et al, 2015 ; Herritt et al, 2018 ; Luo et al, 2018 ). For small experiments where only a few cultivars/species are to be analyzed, it is more reasonable to do standard A-Ci curve measurements even if it is more time consuming, as they can be used to obtain other important information such as C c , g m ( Harley et al, 1992 ), R d and Γ that can give further valuable information about the physiological state of the plant.…”

Small Millets for Enduring Food Security Amidst Pandemics

“…Resistant starch content is another important trait specific to millet grain that awaits scientific intervention to unravel its genetics and genomics [ 45 ]. Other prospective areas of research in millets as compared to major cereals include C 4 photosynthetic traits [ 46 , 47 ] and tolerance to multiple environmental stresses [ 48 , 49 ], the development and characterization of male sterility systems [ 33 , 50 ], enhancing the shelf-life (rancidity issues) [ 51 ], reducing grain antinutrients including phytates, phenols, tannins, and enzyme inhibitors [ 52. , 53.…”

“…Resistant starch content is another important trait specific to millet grain that awaits scientific intervention to unravel its genetics and genomics [45]. Other prospective areas of research in millets as compared to major cereals include C 4 photosynthetic traits [46,47] and tolerance to multiple environmental stresses [48,49], the development and characterization of male sterility systems [33,50], enhancing the shelf-life (rancidity issues) [51], reducing grain antinutrients including phytates, phenols, tannins, and enzyme inhibitors [52][53][54], and addressing the issues of lodging and seed-shattering [43,55]. A recent study also reported an increased incidence of insect pests, wherein up to 150 different species were found to attack millets at different growth and developmental stages [31].…”