Photomorphogenic Responses in Maize Seedling Development  

Abstract

As an emerging maize (Zea mays) seedling senses light, there is a decrease in the rate of mesocotyl elongation, an induction of root growth, and an expansion of leaves. In leaf tissues, mesophyll and bundle sheath cell fate is determined, and the proplastids of each differentiate into the dimorphic chloroplasts typical of each cell type. Although it has been inferred from recent studies in several model plant species that multiple photoreceptor systems mediate this process, surprisingly little is known of light signal transduction in maize. Here, we examine two photomorphogenic responses in maize: inhibition of mesocotyl elongation and C4 photosynthetic differentiation. Through an extensive survey of white, red, far-red, and blue light responses among a diverse collection of germplasm, including a phytochrome-deficient mutant elm1, we show that light response is a highly variable trait in maize. Although all inbreds examined appear to have a functional phytochrome signal transduction pathway, several lines showed reduced sensitivity to blue light. A significant correlation was observed between light response and subpopulation, suggesting that light responsiveness may be a target of artificial selection. An examination of C4 gene expression patterns under various light regimes in the standard W22 inbred and elm1 indicate that cell-specific patterns of C4 gene expression are maintained in fully differentiated tissues independent of light quality. To our knowledge, these findings represent the first comprehensive survey of light response in maize and are discussed in relation to maize breeding strategies.The transition from skotomorphogenic to photoautotrophic growth is a complex and highly regulated process that has been the subject of intense study (Nemhauser and Chory, 2002). However, in maize (Zea mays), little is known of the underlying mechanisms governing this transition (Vanderhoef and Briggs, 1978). Under current cultivation practices, maize seeds are sown within a few inches of the soil surface. Soon after germination, the shoot apex, sheathed by the coleoptile, is pushed through the soil by the elongating mesocotyl. Reduced root formation and unexpanded leaves facilitate this rapid upward movement of the shoot apex while expending the least amount of energy from seed reserves. At the soil surface, incident light represses mesocotyl elongation, induces leaf expansion, and promotes root formation. As cells are recruited into emerging leaf primordia, proplastids differentiate into the dimorphic bundle sheath (BS) and mesophyll (M) cell chloroplasts, and the photoautotrophic phase of sporophytic development begins.Light is the most important environmental cue to signal the transition from skotomorphogenesis to photomorphogenesis. In higher plants, phytochromes, cryptochromes, phototropins, and UV-B photoreceptors enable the developing seedling to monitor the quality and flux of incident light (Kevei and Nagy, 2003). The photoreversible phytochromes mediate responses to red (R) and far-red (FR) regions of th...

TheElm1(ZmHy2) Gene of Maize Encodes a Phytochromobilin Synthase

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Evolutionary Convergence of Cell-Specific Gene Expression in Independent Lineages of C4 Grasses

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An Untranslated cis-Element Regulates the Accumulation of Multiple C4 Enzymes in Gynandropsis gynandra Mesophyll Cells

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