A dramatic increase of chlorophyll (Chl) degradation occurs during senescence of vegetative plant organs and fruit ripening. Although the biochemical pathway of Chl degradation has long been proposed, little is known about its regulatory mechanism. Identification of Chl degradation-disturbed mutants and subsequently isolation of responsible genes would greatly facilitate the elucidation of the regulation of Chl degradation. Here, we describe a nonyellowing mutant of Arabidopsis (Arabidopsis thaliana), nye1-1, in which 50% Chl was retained, compared to less than 10% in the wild type (Columbia-0), at the end of a 6-d dark incubation. Nevertheless, neither photosynthesis-nor senescence-associated process was significantly affected in nye1-1. Characteristically, a significant reduction in pheophorbide a oxygenase activity was detected in nye1-1. However, no detectable accumulation of either chlorophyllide a or pheophorbide a was observed. Reciprocal crossings revealed that the mutant phenotype was caused by a monogenic semidominant nuclear mutation. We have identified AtNYE1 by positional cloning. Dozens of its putative orthologs, predominantly appearing in higher plant species, were identified, some of which have been associated with Chl degradation in a few crop species. Quantitative polymerase chain reaction analysis showed that AtNYE1 was drastically induced by senescence signals. Constitutive overexpression of AtNYE1 could result in either pale-yellow true leaves or even albino seedlings. These results collectively indicate that NYE1 plays an important regulatory role in Chl degradation during senescence by modulating pheophorbide a oxygenase activity.

Brassinosteroids (BRs) play an essential role in plant growth and development, and have been implicated in many physiological responses. However, little is known about the role of BRs in the plant response to oxidative stress. In this study, we identified a novel insertion allele (det2-9) of the DET2 gene in Arabidopsis based on molecular, physiological and genetic approaches. We found that the det2 mutant exhibited an enhanced resistance to oxidative stress. The enhanced oxidative stress resistance in det2 plants was correlated with a constitutive increase in superoxide dismutase (SOD) activity and increased transcript levels of the defence gene catalase (CAT). To our knowledge, these results demonstrate, for the first time, that loss-of-function mutations in the DET2 gene lead to an enhanced oxidative stress resistance in Arabidopsis. A general explanation is that the long-term BR deficiency in the det2 mutant results in a constant in vivo physiological stress that, in turn, activates the constitutive expression of some defence genes and, consequently, the activities of related enzymes.

Chlorophyllase (EC 3.1.1.14) is involved in the first step of chlorophyll degradation. Isolation of chlorophyllase genes greatly facilitates characterization of chlorophyllase properties and elucidation of molecular regulation of their in vivo activities. There are two chlorophyllase genes, AtCLH1 and AtCLH2, in Arabidopsis thaliana. The in vivo roles of AtCLH1 have been reported previously. However, few studies have been carried out on AtCLH2. Here, we show that purified recombinant Chlase2, encoded by AtCLH2, exhibits in vitro chlorophyllase activity. Interestingly, "activation" of in vitro activity of the recombinant Chlase2 required higher concentrations of a detergent or a polar solvent. To determine its activity in vivo, the expression of AtCLH2 was inhibited by RNA interference. RNAi plants showed decreased contents of chlorophyllide without a substantial change in the total amount of the extractable chlorophyll and consequently presented lower chlorophyllide to chlorophyll ratios in their leaves. In addition, the two AtCLHs exhibited differential expression patterns. Our results suggest that AtCLH2 might play a distinctive role in chlorophyll catabolism in vivo.

Beauveria brongniartii extracellular subtilisin-like serine protease (Pr1) is one of the most virulent factors by virtue of its activity against insect cuticles. The Pr1 cDNA was cloned using the switching mechanism at the 5' end of the RNA transcript and rapid amplification of cDNA ends. The 1732-bp fragment of genomic DNA containing the predicted open-reading frame of the Pr1 gene was cloned by polymerase chain reaction and sequenced. The Pr1 cDNA is 1550 bp and contains an 1140-bp ORF. The deduced amino-acid sequence of the protein shows identity to that of proteinase K from Tritirachium album (62%), Pr1 from Metarhizium nisopliae (67%), and Pr1 from B. bassiana (76%). The Pr1 protein with an N-terminal fusion to the six-histidine tag was expressed in Escherichia coli as inclusion bodies with the expression vector pBV220. Sodium dodecylsulsulfate-polyacrylamide gel electrophoresis clearly revealed expressed product. The Pr1 protein was purified and refolded and had proteolytic activity of 0.288 U mg(-1).

Endomicroscopy is useful for identifying GM, and GM might be related to FD. These findings could have potential applicability for duodenal screening, and suggest a possible targeting therapy in FD.