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Cotton grown in the United States are day‐length insensitive annuals and are grown under long‐day summers. Photoperiod sensitivity, present in tropical wild and landraces endemic to the center of origin and diversity, is a major barrier for the introgression of tropical gene pool into the US cotton. Previously, we mapped the major photoperiod response locus Gb_Ppd1 on chromosome D06 of Pima cotton (Gossypium barbadense L.). In the current study, an F2 population of 2112 gametes was used to fine map the Gb_Ppd1 locus. Two sequence‐tagged‐site and nine kompetitive allele‐specific polymerase chain reaction (KASP) markers were developed and the Gb_Ppd1 locus was fine mapped to 1.1 cM region flanked by novel markers 17‐KASP‐8, 17‐KASP‐10, and 15‐PR‐10A. The closely linked markers identified 2.10 Mb region in the G. barbadense genome that contained 18 putative gene sequences. A candidate gene Gbar_D06G014560 showed high homology to VASCULAR PLANT ONE ZINC FINGER PROTEIN 1 involved in photoperiodism in Arabidopsis. We evaluated the diagnostic polymorphisms for the flanking markers on a diversity panel of 91 Pima accessions. These markers would be useful in marker‐assisted selection of photoperiod response in cotton breeding. Further, quantitative gene expression analysis indicated that the CONSTANS (CO)/FLOWERING LOCUS T (FT) system is conserved in the photoperiod response pathway in Pima cotton, while CO and FT are likely not the causal genes underlying flowering time at the Gb_Ppd1 locus. The Gb_Ppd1 gene may be an upstream regulatory sequence in the FT gene pathway that controls photoperiodism in photoperiod‐sensitive cotton by affecting the CO/FT interaction under long‐day‐length conditions. Core Ideas: The major effect photoperiod response locus (Gb_Ppd1) of Pima cotton was fine mapped to a 1.1 cM region flanked by new markers 15‐PR‐10A and 17‐KASP‐10.Targeted genomic mapping of Gb_Ppd1 locus identified 18 putative genes in 2.10 Mb region of Gossypium barbadense genome.Candidate gene analyses identified a homolog of VASCULAR PLANT ONE ZINC FINGER PROTEIN 1 as a candidate gene for Gb_Ppd1 locus.Quantitative expression analysis indicated that the CO/FT system in the photoperiod response pathway is likely conserved in Pima cotton, while CO is likely not the causal gene at the Gb_Ppd1 locus. [ABSTRACT FROM AUTHOR]

The genome of Candidatus Liberibacter asiaticus (CLas) reveals the presence of luxR, encodingLuxR protein, one of a two component cell-to-cell communication system. However, the genome lacks the second component, luxl, that produces acyl-homoserine lactones (AHLs), suggesting that CLas has a solo LuxR system. Interestingly, we detected compounds that may act as AHLs in the insect vector (psyllids) that are healthy or infected with CLas, but not in the citrus plants. This finding suggests that the insect is the AHL source. The fact that CLas forms a biofilm on the surface of the insect gut indicates the presence of a cell-cell communication system. Here the system is solo LuxR. Moreover, we have confirmed the activity of CLas-LuxR by its expression in E. coli and detection of LuxR-AHL complex. In order to block the vector transmission of CLas, we produced plants that express LuxR. Insects will acquire CLas and luxR. LuxR will compete with the bacteria for binding to AHL and consequently, CLas will not be able to colonize the insect or form biofilm and fails in the transmission. We aim to provide an environmental friendly solution for the most destructive disease in citrus (Huanglongbing) by producing specific LuxR in citrus to interfere with the vector transmission. As an alternative, we also aim to use synthetic molecules that mimic the specific AHL as an application to disrupt CLas transmission from plant to plant by its vector. More AHL in the insect may confuse the bacteria and induce a strong sticky biofilm that hardly releases cells to plants during insect feeding. Accordingly, the transmission from plant to plant will be diminished or blocked.

Citrus greening disease is a serious bacterial disease of citrus worldwide and is vectored by the Asian citrus pysllid (Diaphorina Citri).  The only effective control strategy includes vigorous control of the psyllid, primarily through heavy reliance on pesticides. As a more sustainable and environmentally friendly method of psyllid control, we evaluated a RNA interference (RNAi) approach based on psyllid oral uptake of dsRNA molecules that target specific psyllid genes.  This approach is based on the finding that cellular uptake of dsRNAs, that match the sequence of essential genes, results in down regulation of those genes and can lead to cell/organism death.  These dsRNA molecules were introduced into the psyllids through feeding on citrus engineered to express the dsRNA using a Citrus tristeza virus as a paratransgenesis vector.  Increased toxicity was observed when adult psyllids were fed on citrus producing dsRNA targeting either gut protease genes.  No increased psyllid toxicity was observed in psyllids fed on citrus producing green fluorescent protein (GFP) dsRNA.  Toxicity related to specific psyllid gene knockout will be discussed.  These results suggest that RNAi-based control may be a viable alternative to current pesticide use for control of psyllids and all phloem feeding pests.

Huanglongbing (HLB) is seriously threatening and causing considerable economic losses to the citrus groves. Its Management depends critically on the control of the Asian citrus Psyllid (ACP), the vector of the cause of HLB, Candidatus Liberibacter asiaticus bacteria (CLas). Silencing genes by RNA interference (RNAi) is a promising technique to control pests. In this study, the abnormal disk wing (awd) has been selected from the available psyllid annotated genome. It has been known that awd gene encodes a nucleoside diphosphate kinase and is associated with wing development. This research focused on the effect of RNAi of awd gene on ACP nymph instars that acquired dsRNA. The Results provide evidence that using the dsRNA of awd gene has diminished the development and survival of ACP nymphs. Moreover, knockdown of awd gene expression was observed through malformation of adult wings. Also, the expression of awd was messured by quantitative PCR (qPCR). Furthermore, we are conducting experiments to investigate awd's possible contribution in temperature tolerance. We attempt to establish effective practical application to prevent the spread of HLB in friendly environmentally strategy.