Search

SUMMARY: Compartmentation of photosynthetic reactions between mesophyll and bundle sheath cells is a key feature of C4 photosynthesis and depends on the cell‐specific accumulation of major C4 enzymes, such as phosphoenolpyruvate carboxylase 1. The ZmPEPC1 upstream region, which drives light‐inducible and mesophyll‐specific gene expression in maize, has been shown to keep the same properties when introduced into rice (C3 plant), indicating that rice has the transcription factors (TFs) needed to confer C4‐like gene expression. Using a yeast one‐hybrid approach, we identified OsbHLH112, a rice basic Helix‐Loop‐Helix (bHLH) TF that interacts with the maize ZmPEPC1 upstream region. Moreover, we found that maize OsbHLH112 homologues, ZmbHLH80, and ZmbHLH90, also interact with the ZmPEPC1 upstream region, suggesting that these C4 regulators were co‐opted from C3 plants. A transactivation assay in maize mesophyll protoplasts revealed that ZmbHLH80 represses, whereas ZmbHLH90 activates, ZmPEPC1 expression. In addition, ZmbHLH80 was shown to impair the ZmPEPC1 promoter activation caused by ZmbHLH90. We showed that ZmbHLH80 and ZmbHLH90 bind to the same cis‐element within the ZmPEPC1 upstream region either as homodimers or heterodimers. The formation of homo‐ and heterodimers with higher oligomeric forms promoted by ZmbHLH80 may explain its negative effect on gene transcription. Gene expression analysis revealed that ZmbHLH80 is preferentially expressed in bundle sheath cells, whereas ZmbHLH90 does not show a clear cell‐specific expression pattern. Altogether, our results led us to propose a model in which ZmbHLH80 contributes to mesophyll‐specific ZmPEPC1 gene expression by impairing ZmbHLH90‐mediated ZmPEPC1 activation in the bundle sheath cells. Significance Statement: Cell‐specific accumulation of major C4 enzymes is a hallmark of C4 photosynthesis. The ZmPEPC1 upstream region is sufficient to drive mesophyll‐specific gene expression in maize (C4 plant) and rice (C3 plant). Here, we report the identification of a rice bHLH TF and its two maize homologues that bind to the ZmPEPC1 upstream region. In addition, we propose a model in which the identified maize TFs contribute to mesophyll‐specific ZmPEPC1 expression. [ABSTRACT FROM AUTHOR]

For thousands of years mythological Lilith has undergone countless transformations. Although she had been created by God himself, just like Adam and Eve, the texts do not pay her as much attention as they do to the first marriage. What is more, contemporary scholars of religious studies throw doubt whether Lilith had even existed. Regardless of the Church's or scholars' acceptance, Lilith seems to be a character invariably present in the worldwide culture. In the dawn of time, she served as a kind of warning, enforcing a more careful childcare - it was believed that if left without a proper care, infants might have been taken or possessed by Lilith; in medieval times she became a symbol of lechery; contemporarily she is mainly associated with bewildering sexual graphics and rare literary presentations which emphasize her intense sexual urges. How such transformations came to be? How the transformation of mythological Lilith over the ages looked like? [ABSTRACT FROM AUTHOR]

C4 photosynthesis has evolved repeatedly from the ancestral C3 state to generate a carbon concentrating mechanism that increases photosynthetic efficiency. This specialized form of photosynthesis is particularly common in the PACMAD clade of grasses, and is used by many of the world's most productive crops. The C4 cycle is accomplished through cell-type-specific accumulation of enzymes but cis -elements and transcription factors controlling C4 photosynthesis remain largely unknown. Using the NADP-Malic Enzyme (NADP-ME) gene as a model we tested whether mechanisms impacting on transcription in C4 plants evolved from ancestral components found in C3 species. Two basic Helix-Loop-Helix (bHLH) transcription factors, ZmbHLH128 and ZmbHLH129, were shown to bind the C4 NADP-ME promoter from maize. These proteins form heterodimers and ZmbHLH129 impairs trans -activation by ZmbHLH128. Electrophoretic mobility shift assays indicate that a pair of cis -elements separated by a seven base pair spacer synergistically bind either ZmbHLH128 or ZmbHLH129. This pair of cis -elements is found in both C3 and C4 Panicoid grass species of the PACMAD clade. Our analysis is consistent with this cis -element pair originating from a single motif present in the ancestral C3 state. We conclude that C4 photosynthesis has co-opted an ancient C3 regulatory code built on G-box recognition by bHLH to regulate the NADP-ME gene. More broadly, our findings also contribute to the understanding of gene regulatory networks controlling C4 photosynthesis. [ABSTRACT FROM AUTHOR]