Etymology Edit

In Mexico, corn smut is known as huitlacoche ( Spanish pronunciation: [(ɡ)witɬaˈkotʃe], sometimes spelled cuitlacoche). This word entered Spanish in Mexico from classical Nahuatl, though the Nahuatl words from which huitlacoche is derived are debated. In modern Nahuatl, the word for huitlacoche is cuitlacochin ( Nahuatl pronunciation: [kʷit͡ɬɑˈkot͡ʃin]), and some sources deem cuitlacochi to be the classical form.[5] Some sources wrongly give the etymology as coming from the Nahuatl words cuitlatl [ˈkʷit͡ɬɑt͡ɬ] ("excrement" or "rear-end", actually meaning "excrescence") and cochtli [ˈkot͡ʃt͡ɬi] ("sleeping", from cochi "to sleep"), thus giving a combined mismeaning of "sleeping/hibernating excrement",[5][6] but actually meaning "sleeping excrescence", referring to the fact that the fungus grows in between the corns and impedes them from developing, thus they remain "sleeping". A second group of sources deem the word to mean "raven's excrement".[7][8] These sources appear to be combining the word cuitlacoche for "thrasher"[9] with cuitla, meaning "excrement", actually meaning "excrescence". However, the avian meaning of cuitlacoche derives from the Nahuatl word "song" cuīcatl [ˈkʷiːkɑt͡ɬ], itself from the verb "to sing" cuīca [ˈkʷiːkɑ].[5] This root then clashes with this reconstruction's second claim that the segment cuitla- comes from cuitla ("excrement"). One source derives the meaning as "corn excrescence", using cuītla again and "maize" tlaōlli [t͡ɬɑˈoːlːi].[10] This requires the linguistically unlikely evolution of tlaole "maize" into tlacoche.

Characteristics Edit

The fungus infects all parts of the host plant by invading the ovaries of its host. The infection causes the corn kernels to swell up into tumor-like galls, whose tissues, texture and developmental pattern are mushroom-like. These galls are made up of hypertrophied cells of the infected plant, along with resulting fungal threads, and blue-black spores.[11] These dark-colored spores give the cob a burned, scorched appearance; this is the origin of the generic name Ustilago, from the Latin word ustilare (to burn).

Biology Edit

Life cycle Edit Ustilago maydis haploid sporidia haploid sporidia When grown in the lab on very simple media, it behaves like baker's yeast, forming single cells called sporidia. These cells multiply by budding off daughter cells. When two compatible sporidia meet on the surface of the plant, they switch to a different mode of growth. First, they send out conjugation tubes to find each other, after which they fuse and make a hypha to enter the maize plant. Hyphae growing in the plant are dikaryotic; they possess two haploid nuclei per hyphal compartment. In contrast to sporidia, the dikaryotic phase of U. maydis requires infection of the plant to grow and differentiate, and cannot be maintained in the laboratory. Proliferation of the fungus inside the plant leads to disease symptoms such as chlorosis, anthocyanin formation, reduced growth, and the appearance of tumors harboring the developing teliospores.[12][13] Mature spores are released from the tumors and spread by rain and wind. Under appropriate conditions, a metabasidium is formed in which meiosis occurs. Resulting haploid nuclei migrate into elongated single cells. These cells detach from the metabasidium to become the sporidia, thus completing the life cycle. Host/pathogen conflict Edit Plants have evolved efficient defense systems against pathogenic microbes. A rapid plant defense reaction after pathogen attack is the oxidative burst, which involves the production of reactive oxygen species at the site of the attempted invasion. As a pathogen, U. maydis can respond to such an oxidative burst by an oxidative stress response, regulated by gene YAP1. This response protects U. maydis from the host attack, and is necessary for the pathogen’s virulence.[14] Furthermore, U. maydis has a well-established recombinational DNA repair system.[15] This repair system involves a homolog of Rad51 that has a very similar sequence and size to its mammalian counterparts. This system also involves a protein, Rec2 that is more distantly related to Rad51, and Brh2 protein that is a streamlined version of the mammalian Breast Cancer 2 (BRCA2) protein. When any of these proteins is inactivated, sensitivity of U. maydis to DNA damaging agents is increased. Also mitotic recombination becomes deficient, mutation frequency increases and meiosis fails to complete. These observations suggest that recombinational repair during mitosis and meiosis in U. maydis may assist the pathogen in surviving DNA damage arising from the host’s oxidative defensive response to infection, as well as from other DNA damaging agents.

Uses Edit

Nutritional value Edit

When corn smut grows on a corn cob, it changes the nutritional worth of the corn it affects. Corn smut contains much more protein than regular corn does. The amino acid lysine, of which corn contains very little, abounds in corn smut.[26]

See also Edit