Phospholipase D (PLD) and its product, phosphatidic acid (PA), play key roles in cellular processes, including stress and hormonal responses, vesicle trafficking, and cytoskeletal rearrangements. We isolated and functionally characterized Arabidopsis thaliana PLDz2, which is expressed in various tissues and enhanced by auxin. A PLDz2-defective mutant, pldz2, and transgenic plants deficient in PLDz2 were less sensitive to auxin, had reduced root gravitropism, and suppressed auxindependent hypocotyl elongation at 298C, whereas transgenic seedlings overexpressing PLDz2 showed opposite phenotypes, suggesting that PLDz2 positively mediates auxin responses. Studies on the expression of auxin-responsive genes and observation of the b-glucuronidase (GUS) expression in crosses between pldz2 and lines containing DR5-GUS indicated that PLDz2, or PA, stimulated auxin responses. Observations of the membrane-selective dye FM4-64 showed suppressed vesicle trafficking under PLDz2 deficiency or by treatment with 1-butanol, a PLD-specific inhibitor. By contrast, vesicle trafficking was enhanced by PA or PLDz2 overexpression. Analyses of crosses between pldz2 and lines containing PIN-FORMED2 (PIN2)-enhanced green fluorescent protein showed that PLDz2 deficiency had no effect on the localization of PIN2 but blocked the inhibition of brefeldin A on PIN2 cycling. These results suggest that PLDz2 and PA are required for the normal cycling of PIN2-containing vesicles as well as for function in auxin transport and distribution, and hence auxin responses.

FAR-RED ELONGATED HYPOCOTYL3 (FHY3) and its homolog FAR-RED IMPAIRED RESPONSE1 (FAR1), two transposasederived transcription factors, are key components in phytochrome A signaling and the circadian clock. Here, we use chromatin immunoprecipitation-based sequencing (ChIP-seq) to identify 1559 and 1009 FHY3 direct target genes in darkness (D) and far-red (FR) light conditions, respectively, in the Arabidopsis thaliana genome. FHY3 preferentially binds to promoters through the FHY3/FAR1 binding motif (CACGCGC). Interestingly, FHY3 also binds to two motifs in the 178-bp Arabidopsis centromeric repeats. Comparison between the ChIP-seq and microarray data indicates that FHY3 quickly regulates the expression of 197 and 86 genes in D and FR, respectively. FHY3 also coregulates a number of common target genes with PHYTOCHROME INTERACTING FACTOR 3-LIKE5 and ELONGATED HYPOCOTYL5. Moreover, we uncover a role for FHY3 in controlling chloroplast development by directly activating the expression of ACCUMULATION AND REPLICATION OF CHLOROPLASTS5, whose product is a structural component of the latter stages of chloroplast division in Arabidopsis. Taken together, our data suggest that FHY3 regulates multiple facets of plant development, thus providing insights into its functions beyond light and circadian pathways.

We studied the interactive effects of pCO2 and growth light on the coastal marine diatom Thalassiosira pseudonana CCMP 1335 growing under ambient and expected end-of-the-century pCO2 (750 ppmv), and a range of growth light from 30 to 380 µmol photons·m−2·s−1. Elevated pCO2 significantly stimulated the growth of T. pseudonana under sub-saturating growth light, but not under saturating to super-saturating growth light. Under ambient pCO2 susceptibility to photoinactivation of photosystem II (σi) increased with increasing growth rate, but cells growing under elevated pCO2 showed no dependence between growth rate and σi, so under high growth light cells under elevated pCO2 were less susceptible to photoinactivation of photosystem II, and thus incurred a lower running cost to maintain photosystem II function. Growth light altered the contents of RbcL (RUBISCO) and PsaC (PSI) protein subunits, and the ratios among the subunits, but there were only limited effects on these and other protein pools between cells grown under ambient and elevated pCO2.