The Relationship Between Sugar Metabolism In Anther Of Physiological Male Sterile Line And Expression Of Corresponding Regulatory Genes In Wheat

To date, utilization of heterosis in wheat production has been mainly realized throughcytoplasmic male sterile (CMS) or by means of chemical hybridizing agent (CHA).Compared with CMS, an effective CHA allows the production of a great number of parentalcombinations and allows the evaluation of a high number of lines for combining capacity andgenetic value. The underlying mechanism by which CHA induces wheat pollen sterility is stillnot understood.Carbohydrate are the primary source of energy and are important in the accomplishmentof reproductive development in plants. Apart from their role as substrates in carbohydratemetabolism, sugars also play roles as principal messengers of signal transduction, similar tophytohormones. With a view to understanding the relationship between carbohydratemetabolism and physiological male steril (PHYMS) induced by SQ-1, the morphologicalchanges of anther tapetum and the expression of sucrose metabolism related genes, one SUTgene (TaSUT1), one CWIN gene IVR1and one vacuolar invertase (VIN) gene IVR5, fromdifferent developmental stages of anthers were analyzed via paraffin section and qRT-PCR.Moreover, acid invertase activities and soluble sugar content were also determined andcompared between the PHYMS line and the fertile line. The main results obtained were asfollow:(1) Vegetative and floral development seemed to be normal in the PHYMS line, and thePHYMS line pistils appeared normal, while those anthers of the PHYMS line were relativelysmaller. The scanning electron microscopy (SEM) indicated that the PHYMS line pollen grainwas seriously empty and shrunken. Transverse sections showed that, At the mninucleateprophase, the PHYMS line anther tapetum showed delayed degradation and was thicker thanthe fertile line. At the trinucleate stage, the PHYMS line pollen grains were lack of starch,lipids, and other storage materials.(2) The PHYMS line anthers starch content had no difference with the fertile line untilthe binucleate stage. At the trinucleate stage, the PHYMS line anthers had approximately55%lower starch content than those from normal lines. Compared with the fertile line, the levelsof total soluble sugars in the PHYMS line anthers increased at the meiosis stage, mninucleate prophase and binucleate stage, and decreased at the mninucleate anaphase. Reducing sugarslevels in the fertile line anthers were similar with the total soluble sugars levels. Comparedwith the fertile line, the levels of reducing sugars in the PHYMS line anthers increased at themninucleate prophase and binucleate stage, and decreased at the mninucleate anaphase andtrinucleate stage. In the fertile line anthers, the levels of non-reducing sugars increasedgradually from meiosis to a minimum at trinucleate stage. The amount of non-reducing sugarsin the PHYMS line always remained higher than in the fertile line.(3) CWIN and VIN activities in anthers of the fertile line increased steadily andsubstantially during pollen maturation. Although activities in the PHYMS line anthersincreased steadily, they remained substantially below than those in the normal lines.(4) Compared with the fertile line, the TaSUT1transcript level in the PHYMS lineanthers became less abundant in anthers at the mninucleate prophase; Compared with thefertile line, the expression of IVR1and IVR5in the PHYMS line anthers were slightlydecreased at the meiosis stage and significantly down-regulated at the mninucleate prophaseand the mninucleate anaphase.In conclusion, it was likely that SQ-1treatment caused delayed tapetal degeneration,causing the blockage of nutrients (including carbohydrate, lipidic molecules, and othersubstances) supply to the young microspores, resulting in abnormal pollen development andmale sterility. The corresponding changes between the expression of these two invertase genesand their enzyme activities, indicated that the sugar transport might be disrupted from tapetumto microspores, resulting in microspores abortion. Thus, the mechanism of PHYMS is closelyrelated to sugar transport disruption.