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The β-ketoacyl-acyl carrier protein synthase I (KASI) is involved in de novo fatty acid biosynthesis in many organisms. Two putative KASI genes, JcKASI-1 and JcKASI-2, were isolated from Jatropha curcas. The deduced amino acid sequences of JcKASI-1 and JcKASI-2 exhibit around 83.8% and 72.5% sequence identities with AtKASI, respectively, and both contain conserved Cys-His-Lys-His-Phe catalytic active sites. Phylogenetic analysis indicated that JcKASI-2 belongs to a clade with several KASI proteins from dicotyledonous plants. Both JcKASI genes were expressed in multiple tissues, most strongly in filling stage seeds of J. curcas. Additionally, the JcKASI-1 and JcKASI-2 proteins were both localized to the plastids. Expressing JcKASI-1 in the Arabidopsis kasI mutant rescued the mutant's phenotype and restored the fatty acid composition and oil content in seeds to wild-type, but expressing JcKASI-2 in the Arabidopsis kasI mutant resulted in only partial rescue. This implies that JcKASI-1 and JcKASI-2 exhibit partial functional redundancy and KASI genes play a universal role in regulating fatty acid biosynthesis, growth, and development in plants.

The Stay-Green Rice (SGR) protein is encoded by the SGR gene and has been shown to affect chlorophyll (Chl) degradation during natural and dark-induced leaf senescence. An SGR homologue, SGR-like (SGRL), has been detected in many plant species. We show that SGRL is primarily expressed in green tissues, and is significantly downregulated in rice leaves undergoing natural and dark-induced senescence. As the light intensity increases during the natural photoperiod, the intensity of SGRL expression declines while that of SGR expression increases. Overexpression of SGRL reduces the levels of Chl and Chl-binding proteins in leaves, and accelerates their degradation in dark-induced senescence leaves in rice. Our results suggest that the SGRL protein is also involved in Chl degradation. The relationship between SGRL and SGR and their effects on the degradation of the light-harvesting Chl a/b-binding protein are also discussed.

Linoleic acid (LA, C18:2) and α-linolenic acid (ALA, C18:3) are polyunsaturated fatty acids (PUFAs) and major storage compounds in plant seed oils. Microsomal ω-6 and ω-3 fatty acid (FA) desaturases catalyze the synthesis of seed oil LA and ALA, respectively. Jatropha curcas L. seed oils contain large proportions of LA, but very little ALA. In this study, two microsomal desaturase genes, named JcFAD2 and JcFAD3, were isolated from J. curcas. Both deduced amino acid sequences possessed eight histidines shown to be essential for desaturases activity, and contained motif in the C-terminal for endoplasmic reticulum localization. Heterologous expression in Saccharomyces cerevisiae and Arabidopsis thaliana confirmed that the isolated JcFAD2 and JcFAD3 proteins could catalyze LA and ALA synthesis, respectively. The results indicate that JcFAD2 and JcFAD3 are functional in controlling PUFA contents of seed oils and could be exploited in the genetic engineering of J. curcas, and potentially other plants.

Pheophorbide a oxygenase (PAO) and red chlorophyll catabolite reductase (RCCR) catalyze key steps in chlorophyll degradation by opening the porphyrin macrocycle of pheophorbide a and forming the primary non-photoreactive fluorescent chlorophyll catabolite. These genes strongly participate in senescence and reportedly involved in plants' responses to physical wounding and pathogens. In this report, a single PAO gene (OsPAO) and two RCCR genes (OsRCCR1 and OsRCCR2) have been isolated from rice. Expression analysis by semi-quantitative PCR or quantitative real-time PCR showed that OsRCCR1 transcripts were much more abundant than OsRCCR2, and all of these genes were upregulated during senescence and following wound treatment. RNA interference knockdown of OsPAO led to pheophorbide a accumulation in leaves (especially dark-induced senescent leaves) and leaf death from regeneration stage onwards, even transgenic plants inviability after transplantation. While, knockdown of OsRCCR1 resulted in lesion-mimic spots generation in older leaves which died off early in the transgenic plants. These results suggest that OsPAO and OsRCCR1 play key roles in senescence and are involved in wound responses.