Evolutionary and Functional Analysis of a Chara Plasma Membrane H+-ATPase.

H+-ATPases are the main transporters in plant and fungal plasma membranes (PMs), comparable to the Na+/K+ ATPases in animal cells. At the molecular level, most studies on the PM H+-ATPases have been focused on land plants and fungi (yeast). The research of PM H+-ATPases in green algae falls far behind due to the lack of genetic information. Here we studied a potential PM H+-ATPase (CHA1) from Chara australis, a species of green algae belonging to the division Charophyta, members of which are considered to be one of the closest ancestors of land plants. The gene encodes a 107 kDa protein with all 6 P-type ATPase-specific motifs and a long, diverse C-terminal domain. A new amino acid sequence motif R*****Q in transmembrane segment 5 was identified among the known PM H+-ATPases from Charophyta and Chlorophyta algae, which is different from the typical PM H+-ATPases in yeast or land plants. Complementation analysis in yeast showed that CHA1 could successfully reach the PM, and that proton pump activity was obtained when the last 77 up to 87 amino acids of the C-terminal domain were deleted. PM localization was confirmed in Arabidopsis protoplasts; however, deletion of more than 55 amino acids at the N-terminus or more than 98 amino acids at the C-terminus resulted in failure of CHA1 to reach the PM in yeast. These results suggest that an auto-inhibition domain is located in the C-terminal domain, and that CHA1 is likely to have a different regulation mechanism compared to the yeast and land plant PM H+-ATPases.

PIN-driven polar auxin transport in plant developmental plasticity: a key target for environmental and endogenous signals.

Plants master the art of coping with environmental challenges in two ways: on the one hand, through their extensive defense systems, and on the other, by their developmental plasticity. The plant hormone auxin plays an important role in a plant's adaptations to its surroundings, as it specifies organ orientation and positioning by regulating cell growth and division in response to internal and external signals. Important in auxin action is the family of PIN-FORMED (PIN) auxin transport proteins that generate auxin maxima and minima by driving polar cell-to-cell transport of auxin through their asymmetric subcellular distribution. Here, we review how regulatory proteins, the cytoskeleton, and membrane trafficking affect PIN expression and localization. Transcriptional regulation of PIN genes alters protein abundance, provides tissue-specific expression, and enables feedback based on auxin concentrations and crosstalk with other hormones. Post-transcriptional modification, for example by PIN phosphorylation or ubiquitination, provides regulation through protein trafficking and degradation, changing the direction and quantity of the auxin flow. Several plant hormones affect PIN abundance, resulting in another means of crosstalk between auxin and these hormones. In conclusion, PIN proteins are instrumental in directing plant developmental responses to environmental and endogenous signals.

Parthenocarpic potential in Capsicum annuum L. is enhanced by carpelloid structures and controlled by a single recessive gene.

BACKGROUND: Parthenocarpy is a desirable trait in Capsicum annuum production because it improves fruit quality and results in a more regular fruit set. Previously, we identified several C. annuum genotypes that already show a certain level of parthenocarpy, and the seedless fruits obtained from these genotypes often contain carpel-like structures. In the Arabidopsis bel1 mutant ovule integuments are transformed into carpels, and we therefore carefully studied ovule development in C. annuum and correlated aberrant ovule development and carpelloid transformation with parthenocarpic fruit set. RESULTS: We identified several additional C. annuum genotypes with a certain level of parthenocarpy, and confirmed a positive correlation between parthenocarpic potential and the development of carpelloid structures. Investigations into the source of these carpel-like structures showed that while the majority of the ovules in C. annuum gynoecia are unitegmic and anatropous, several abnormal ovules were observed, abundant at the top and base of the placenta, with altered integument growth. Abnormal ovule primordia arose from the placenta and most likely transformed into carpelloid structures in analogy to the Arabidopsis bel1 mutant. When pollination was present fruit weight was positively correlated with seed number, but in the absence of seeds, fruit weight proportionally increased with the carpelloid mass and number. Capsicum genotypes with high parthenocarpic potential always showed stronger carpelloid development. The parthenocarpic potential appeared to be controlled by a single recessive gene, but no variation in coding sequence was observed in a candidate gene CaARF8. CONCLUSIONS: Our results suggest that in the absence of fertilization most C. annuum genotypes, have parthenocarpic potential and carpelloid growth, which can substitute developing seeds in promoting fruit development.